Diferenças adaptativas entre plantas de savanas e...

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Maíra Figueiredo Goulart Diferenças adaptativas entre plantas de savanas e florestas: o caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae) do Cerrado e da Mata Atlântica Tese apresentada ao programa de pós-graduação em Ecologia, Conservação e Manejo de Vida Silvestre da Universidade Federal de Minas Gerais como requisito parcial para obtenção do título de Doutor. Orientador: Prof. Dr. José Pires de Lemos Filho Co-orientador: Profa. Dra. Maria Bernadete Lovato Belo Horizonte 2008

Transcript of Diferenças adaptativas entre plantas de savanas e...

Page 1: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

Maíra Figueiredo Goulart

Diferenças adaptativas entre plantas de savanas e florestas:

o caso das populações de Plathymenia reticulata

(Leguminosae-Mimosoideae) do Cerrado e da Mata Atlântica

Tese apresentada ao programa de pós-graduação em Ecologia, Conservação e Manejo de Vida Silvestre da Universidade Federal de Minas Gerais como requisito parcial para obtenção do título de Doutor.

Orientador: Prof. Dr. José Pires de Lemos Filho

Co-orientador: Profa. Dra. Maria Bernadete Lovato

Belo Horizonte

2008

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Aos que plantam árvores.

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“São seis ou são seiscentas

distâncias que se cruzam, se dilatam

no gesto, no calar, no pensamento?

Que léguas de um a outro irmão.

Entretanto, o campo aberto, os mesmos copos,

o mesmo vinhático das camas iguais.

A casa é a mesma.

Igual, vista por olhos diferentes?”

Carlos Drummond Andrade

(Irmão, Irmãos)

“Mas se deu que, certo dia, nosso pai mandou fazer para si uma canoa.

Era a sério. Encomendou a canoa especial, de pau de vinhático, pequena,

mal com a tabuinha da popa, como para caber justo o remador.

Mas teve de ser toda fabricada, escolhida forte e arqueada em rijo,

própria para dever durar na água por uns vinte ou trinta anos.

(...) E esquecer não posso, do dia em que a canoa ficou pronta”.

João Guimarães Rosa

(A Terceira Margem do Rio)

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ÍNDICE

Agradecimentos ............................................................................................................

Resumo .........................................................................................................................

Abstract ........................................................................................................................

Apresentação

- Introdução ............................................................................................................

- Espécie estudada ..................................................................................................

- Contextualização dos estudos ..............................................................................

- Estrutura da tese ..................................................................................................

- Referências bibliográficas ...................................................................................

Capítulo 1: Evidences for local adaptations from early developmental

responses to light and soil fertility in the tropical tree Plathymenia reticulata

along a forest-savanna boundary

- Introduction .........................................................................................................

- Material and methods

- Studied tree species ....................................................................................

- Studied populations, seeds collection and germination .............................

- Non destructive experiment .......................................................................

- Destructive experiment ..............................................................................

- Analysis of data .........................................................................................

- Results .................................................................................................................

- Discussion

- Differences among populations .................................................................

- Ecotypic differentiation .............................................................................

- Evolutionary trends in savanna-forest boundary .......................................

- References ...........................................................................................................

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Capítulo 2: To which extent phenotypic plasticity in response to light is

involved in the ecotypic differentiation of a tree species from savanna and

forest habitats?

- Introduction .........................................................................................................

- Material and methods

- Studied populations ...................................................................................

- Experimental design ..................................................................................

- Morphological and physiological measurements ......................................

- Analysis of data .........................................................................................

- Results .................................................................................................................

- Discussion

- Phenotypic plasticity in response to light ..................................................

- Functional heterogeneity of the light environment ....................................

- Functional traits and ecotypic differentiation ............................................

- References ...........................................................................................................

Capítulo 3: How important is soil fertility in driving ecotypic differentiation of

a tropical tree species from savanna and forest habitats?

- Introduction .........................................................................................................

- Material and methods

- Studied populations ...................................................................................

- Nursery experiment and data collection ....................................................

- Field experiment and survival censures .....................................................

- Analysis of data .........................................................................................

- Results .................................................................................................................

- Discussion

- Responses to soil ........................................................................................

- Habitat specialization .................................................................................

- Phenotypic plasticity ..................................................................................

- Survival in field conditions ........................................................................

- Concluding remarks ...................................................................................

- References ..................................................................................................................

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AGRADECIMENTOS

Ao Prof. José Pires e à Profa. Bernadete, orientadores com os quais iniciei minha

formação acadêmica já faz muitos anos, serei eternamente grata por terem me proporcionado

incontáveis oportunidades de aprendizado, por toda a confiança em mim depositada e por serem

sempre um estímulo a seguir em frente.

Ao Fernando Valladares, meu orientador durante um estágio “sanduíche” no Centro de

Ciencias Medioambientales do Consejo Superior de Investigaciones Científicas em Madri,

Espanha. Inicialmente, o objetivo do estágio foi aprender a usar índices para estimativa de

plasticidade fenotípica e sua interpretação, mas a orientação do Fernando transcendeu os

objetivos e suas boas idéias foram muito importantes para a interpretação e discussão de todos

dados, bem como para redação dos manuscritos. Portanto, agradeço muitíssimo a enormidade de

coisas que aprendi. Agradeço ainda a todos do Grupo de Ecología Mediterránea pelo empenho

em compreender meu “portunhol” e por me proporcionarem um ambiente de trabalho tão

amigável. Agradeço, em especial, as amigas Teresa Gimeno e Virginia Gancedo, por

transformarem a casa em lar.

Fernanda Barros esteve presente desde os primeiros rascunhos dos experimentos,

auxiliando-me em todas as etapas dos trabalhos e sempre foi uma verdadeira amiga. Sérgio

Teles apresentou-se como um estagiário incansável, sempre disposto a aprender. A disposição

dos dois em medir centenas de plantas em situações nada confortáveis foi para mim um grande

estímulo e, definitivamente, não teria chegado até aqui sem essa valiosa ajuda, pela qual sou

muito grata. Agradeço às outras pessoas que contribuiram para a coleta dos dados: Alex,

Letícia, Eugênio, Ana Clara, Marcos, Renan, Viviane, Carmem e Socorro, e ao Sr. José dos

Reis, que cuidou diariamente das plantas no viveiro, sempre de forma muito atenciosa.

Sou grata às instituições que me apoiaram financeiramente: CAPES (Coordenação de

Aperfeiçoamento de Pessoal de Nível Superior) e CNPq (Conselho Nacional de

Desenvolvimento Científico e Tecnológico), pelas bolsas concedidas, respectivamente de

doutorado e doutorado-sanduíche; FAPEMIG (Fundação de Amparo à Pesquisa do Estado

de Minas Gerais) financiadora do projeto de pesquisa “Abordagem filogeográfica e

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ecofisiológica em populações de leguminosas arbóreas da Mata Atlântica e do Cerrado”, cujos

recursos possibilitaram a coleta de muitos dos dados abordados na tese.

Sinto-me privilegiada em agradecer a três universidades: à Universidade Federal de

Minas Gerais por fazer parte da minha vida há 10 anos. Ao curso de graduação em Ciências

Biológicas e ao curso de pós-graduação em Ecologia, Conservação e Manejo da Vida Silvestre,

todos os professores e colegas, pelo imensurável aprendizado. Agradeço à Universidade Federal

de Ouro Preto, que me proporcionou uma experiência didática tão profunda. Aos professores do

Departamento de Ciências Biológicas, agradeço por terem confiado em mim tantas

responsabilidades, e agradeço ainda aos meus alunos dos cursos de Ciências Biológicas,

Turismo e Engenharia Ambiental, com quem tanto aprendi. Também sou grata à Universidade

Federal dos Vales do Jequitinhonha e Mucuri, na qual ingressar como professora foi a

realização de um sonho, reconheço que a redação desta tese ainda não estaria finalizada se não

fosse o apoio que recebi do Departamento de Ciências Biológicas.

Apenas uma parte do meu aprendizado durante o doutorado está apresentada nessa tese.

A outra parte não pode ser expressa em números e nem ser divulgada em artigos científicos,

mas representa um aprendizado fundamental na minha vida. Deixo registrado um agradecimento

muito especial ao Instituto Biotrópicos de Pesquisa em Vida Silvestre por tantas oportunidades

de crescimento humano e profissional. Aos colegas da Biotrópicos, por serem amigos e

companheiros empenhados em continuar sonhando com um futuro de mais harmonia com a

natureza, apesar da dura rotina que a ciência nos impõe.

Agradeço a todos que compartilham da minha alegria em ver as plantas crescendo

verdinhas. Aos meus amigos e às minhas queridas famílias, pela alegria de viver. Aos meus

avós, que são as pessoas mais amorosas que conheço, em especial, agradeço ao vô Thadeu por

ter deixado tantas boas lembranças. Ao Nando, agradeço por compartilhar comigo a vida de

biólogo desde a nossa infância. Aos meus pais, corujas incondicionais, minha mais profunda

gratidão por todo o apoio, o aprendizado e o maior amor do mundo. Ao Alex que, enquanto

colega, compartilhou comigo todas as angústias e as alegrias do desenrolar dos nossos

doutorados, e que, enquanto marido, traz flores para o jardim. Obrigada por ser meu melhor

amigo, meu atencioso confidente e meu maior incentivador.

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RESUMO

Esta tese aborda diferenças adaptativas entre populações da arbórea Plathymenia reticulata

(Leguminosae-Mimosoideae) no Cerrado e na Mata Atlântica. Indivíduos de quatro populações

naturais desta espécie (uma em área “core” de cada bioma e duas em região ecotonal entre eles,

a primeira com fisionomia de Cerrado e a segunda de Mata Atlântica) foram crescidos em

viveiro e submetidos a quatro tratamentos de luz (100, 53, 36 e 22% da luz solar plena) e dois

tratamentos de solo (solo de Cerrado e de Mata Atlântica). Em cada tratamento, a avaliação de

características como morfologia, crescimento, fotossíntese e pigmentos foliares, forneceu uma

indicação da extensão das diferenças genéticas entre as populações. Para uma mesma população

a comparação entre os tratamentos permitiu uma avaliação da plasticidade fenotípica. Os

resultados mostraram diversas diferenças entre populações de P. reticulata do Cerrado e da

Mata Atlântica durante o crescimento inicial. Freqüentemente, os indivíduos das populações em

região de ecótone apresentaram valores intermediários para as características avaliadas. Quanto

à morfologia e ao crescimento, comparativamente, as plantas do Cerrado mostraram

características de resistência à estresses, enquanto as plantas da Mata Atlântica apresentaram

características de tolerância à sombra e maior habilidade competitiva. A avaliação dos

pigmentos foliares apontou para um padrão de que as plantas do Cerrado tendem a apresentar

um maior investimento em fotoproteção e as de Mata Atlântica em captação de luz. Os

caracteres relacionados à fotossíntese, avaliados pela fluorescência da clorofila, mostraram-se

conservados entre as populações. Foi encontrada menor plasticidade fenotípica em resposta à

luz na população de Cerrado do que na de Mata Atlântica, bem como um padrão geral de maior

plasticidade em reposta ao solo nas populações de ecótone do que nas de área “core” dos

biomas. Após um ano de crescimento em condições de viveiro, os indivíduos foram

transplantados para o campo. Censos de sobrevivência não mostraram diferenças significativas

entre as populações nos primeiros vinte meses. Coletivamente, os resultados dos experimentos

no viveiro mostram que as populações de P. reticulata são adaptadas ao ambiente de luz e às

condições de solo do seu bioma de origem, caracterizando a existência de ecótipos de savana e

floresta nesta espécie. É discutido como a seleção natural está atuando na promoção de

diferenças entre os ecótipos, como fatores luz e solo estão envolvidos neste processo, quais são

as tendências evolutivas na região de ecótone e como investigações futuras dos indivíduos

transplantados podem acrescentar a este conhecimento.

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ABSTRACT

This thesis investigates adaptive differences between populations of the tree Plathymenia

reticulata (Leguminosae-Mimosoideae) in the Cerrado and the Atlantic Forest. Individuals from

four natural populations (one from each biome core area and two from ecotonal region, the first

with Cerrado physiognomy and the other with Atlantic Forest physiognomy) were grown in a

nursery with four different light treatments (100, 53, 36 and 22% of full sunlight) and two soil

treatments (Cerrado and Atlantic Forest soils). At each treatment, comparisons of traits such as

morphology, growth, photosynthesis and leaf pigments, provided an indication of the extent of

genetic differences; for individual populations, comparisons of different treatments allowed the

assessment of the phenotypic plasticity. The results showed several differences in P. reticulata

from Cerrado and Atlantic Forest core populations during the seedling and sapling phases.

Frequently, individuals in the ecotonal populations showed intermediate values. Comparatively,

concerning morphology and growth, plants from Cerrado were characterized by more stress

resistance traits while plants from Atlantic Forest showed more evident shade avoidance traits

and higher competitive ability. Leaf pigment evaluation showed that plants from Cerrado

invested comparatively more in maximizing photoprotection and plants from Atlantic Forest in

improving light interception. Photosynthesis traits related to chlorophyll fluorescence were very

conserved among populations. We found lower levels of plasticity in response to light in

Cerrado than in Atlantic Forest core populations, and a general pattern of higher levels in

plasticity in response to soil in ecotonal populations than in core populations. After one year of

growth in the nursery, individuals were transplanted into field conditions. Survival censors

showed no significant differences among populations in the first twenty months. Collectively,

the results from the nursery experiments showed that populations of P. reticulata are locally

adapted to the light environment and the soil properties from their home habitat, which

characterizes the existence of distinct savanna and forest ecotypes in this species. It is discussed

how natural selection is promoting the differences between ecotypes, how light and soil is

involved in this process, which are the evolutionary trends in the biomes’ boundary and how

further evaluations of individuals in the field should add to this knowledge.

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APRESENTAÇÃO

Introdução

A ecologia funcional é o ramo da Ecologia que busca explicar a distribuição das

espécies ou genótipos baseado nas características funcionais dos mesmos, como

atributos fisiológicos, morfológicos, anatômicos e de história de vida (Poorter e Garnier

2007). Normalmente os estudos de ecologia funcional são realizados por meio de

comparações, buscando compreender, por exemplo, diferenças entre plantas pioneiras e

plantas clímax (Westoby 2007). A maioria dos estudos compara o desempenho médio

de indivíduos de diferentes grupos, porém a avaliação da plasticidade das respostas dos

indivíduos em um mesmo grupo vem ganhando importância nos últimos anos. Tem sido

demonstrado que esta plasticidade desempenha um papel crítico na resposta dos

indivíduos aos fatores ambientais, influenciando, portanto, a ecologia e a distribuição

dos mesmos (Valladares et al. 2000a, b).

Estudos sobre ecologia funcional podem ser conduzidos em escalas

macroevolutiva e microevolutiva. Na primeira, é enfocada a comparação entre espécies,

buscando compreender padrões gerais. Na escala microevolutiva são comparadas

populações ou genótipos de uma única espécie, permitindo o estudo na escala real em

que a evolução atua, uma vez que o processo evolutivo inicia-se com a alteração de

freqüências gênicas entre populações (Ridley 2004).

Nos estudos que compõem esta tese, microevolução de plantas na Mata

Atlântica e no Cerrado é abordada com objetivo geral de acrescentar dados ao

conhecimento sobre ecologia funcional e plasticidade fenotípica das mesmas. Os

resultados são discutidos do ponto de vista evolutivo, buscando contribuir para a

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compreensão das características que evoluem de forma diferenciada entre as plantas que

colonizam savanas e florestas.

Espécie estudada

Foram avaliadas populações de Plathymenia reticulata (Leguminosae-

Mimosoideae) uma leguminosa arbórea conhecida popularmente como vinhático, nome

que se refere à coloração vinho da madeira (Silva Júnior 2005). Esta espécie é

amplamente distribuída pelo território brasileiro, ocorrendo em pelo menos 15 estados,

especialmente em áreas de Cerrado e Mata Atlântica. Há também registro de sua

ocorrência na Bolívia, Paraguai e Suriname (Warwick e Lewis 2003).

A classificação do gênero Plathymenia foi proposta por G. Bentham em 1842

contendo duas espécies: P. reticulata de ocorrência no Cerrado e P. foliolosa, de

ocorrência na Mata Atlântica. Ao longo do século passado algumas modificações na

sistemática do gênero ocorreram e a existência de apenas uma espécie de Plathymenia

chegou a ser proposta, mas logo refutada (Heringer 1956). Em 2002, os resultados de

um estudo com marcadores moleculares sugeriram fluxo gênico entre as duas espécies

(Lacerda et al. 2002). Em seguida, em 2003, uma revisão taxonômica do gênero foi feita

e apenas P. reticulata passou a ser reconhecida desde então (Warwick e Lewis 2003).

Indivíduos de P. reticulata do Cerrado e da Mata Atlântica diferem-se em

termos de porte. Geralmente os do Cerrado são mais baixos (6 a 12 m), com tronco

retorcido e ramificado, enquanto os da Mata Atlântica são mais altos (15 a 30 m) e

alongados (Figura 1A e B). Indivíduos do Cerrado e da Mata Atlântica compartilham

características gerais como o hábito decíduo, inflorescências formadas por pequenas

flores de coloração esbranquiçada visitadas por pequenos insetos, e sementes aladas

dispersas pelo vento (Figura 1C, D e E).

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B A

C

E D 1 cm

Figura 1. Planthymenia reticulata, o vinhático. A) indivíduo do Cerrado; B) indivíduo da Mata Atlântica;

C) inflorescências; D) frutos maduros; E) frutos, sementes com e sem artículo endocárpico. (Fotos: M. F. Goulart)

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Contextualização dos estudos

Esta tese representa uma continuidade aos estudos que venho desenvolvendo

sobre o vinhático desde 2002, tendo sido também tema da minha dissertação de

mestrado a comparação de populações desta espécie nos diferentes biomas (Goulart

2004). Na ocasião, foram realizadas avaliações baseadas na observação e mensuração

de caracteres dos indivíduos em populações naturais, sobre a fenologia e a morfologia e

dispersão de frutos e sementes. Os resultados indicaram que populações do vinhático

apresentam fenologia semelhante nos diferentes biomas, tendo sido encontrada uma

maior diversidade de comportamentos fenológicos entre indivíduos de uma mesma

população do que entre biomas distintos. Diferenças na fenologia entre populações de

Cerrado e Mata Atlântica são basicamente restritas ao processo de perda de folhas

durante a estação seca, que se inicia com mais antecedência nos indivíduos do Cerrado,

provavelmente em resposta à maior carência de água neste ambiente (Goulart et al.

2005). As sementes dos indivíduos da Mata Atlântica, apesar de apresentarem tamanho

e massa semelhante às do Cerrado, possuem estruturas mais desenvolvidas para

dispersão pelo vento. Este padrão foi interpretado como uma resposta à maior

dificuldade de dispersão por vento imposta pelos ambientes florestais do que os

savânicos (Goulart et al. 2006). Ambos os estudos revelaram um padrão geral de

características intermediárias em populações localizadas em regiões ecotonais entre os

biomas (Goulart et al. 2005, Goulart et al. 2006).

Como uma etapa seguinte a estes trabalhos baseados na observação, iniciei

estudos de experimentação, buscando avaliar a extensão da adaptação das populações de

vinhático ao seu bioma de origem. Conduzi experimentos in situ (em condições de

campo) e ex situ (em viveiro, sob condições ambientais controladas), com o propósito

de avaliar diferenças entre populações de Cerrado, Mata Atlântica e de região ecotonal

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entre os biomas, durante as fases iniciais do desenvolvimento. Experimentos in situ de

longo prazo também foram iniciados para avaliação dos indivíduos em estágios mais

avançados do desenvolvimento. Grande parte dos resultados obtidos até então compõe

esta tese. Para uma melhor contextualização, apresento a seguir algumas informações

gerais sobre os experimentos desenvolvidos.

Experimentos in situ

Foram realizados experimentos de transplante recíproco para testar a hipótese de

que seleção natural é responsável por diferenças entre as populações de vinhático. A

predição foi de que as plantas do Cerrado se estabeleceriam com mais sucesso na área

de Cerrado e as de Mata Atlântica em um sítio de Mata Atlântica, o que demonstraria a

existência de diferenças genéticas relacionadas à adaptação dos indivíduos ao seu

ambiente de origem.

Para estes experimentos, sementes foram coletadas em quatro populações

(Cerrado, Mata Atlântica, ecótone com características de Cerrado e ecótone com

características de Mata Atlântica) e, após escarificação mecânica, foram plantadas em

uma área de Cerrado (município de Lagoa Santa, Minas Gerais) e outra de Mata

Atlântica (município de Ipatinga, Minas Gerais) (Figura 2). Estes experimentos, porém,

se mostraram inconclusivos. Na área do Cerrado, o pisoteamento por gado e a

herbivoria por formigas causou a morte de grande parte das plântulas ou a remoção das

etiquetas com a marcação da procedência. Na área de Mata, o sub-bosque foi alagado no

período de chuvas, causando os mesmos problemas. Por fim, três meses após o plantio,

97% das plântulas provenientes do total de 1600 sementes plantadas estavam mortas ou

foram descartadas por serem de procedência desconhecida. A hipótese foi então testada

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em experimentos ex situ, de forma que as condições controladas e a ausência de

herbívoros pudessem reduzir a mortalidade dos indivíduos.

A

B

Figura 2. Experimento desenvolvido no campo.

A) plantio de sementes escarificadas; B) plântula. (Fotos: M. F. Goulart)

Experimentos ex situ

Sementes das mesmas procedências foram cultivadas em viveiro, submetidas a

diferentes combinações de tratamentos de luz e de solo (Figura 3). Ao longo de sete

meses, medidas morfológicas destrutivas e não destrutivas, medidas de fotossíntese e de

pigmentos foliares foram realizadas. Os resultados destes experimentos estão descritos

nos artigos que compõe esta tese.

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A

B C

Figura 3. Experimentos desenvolvidos em viveiro. A) bancadas com diferentes níveis de sombreamento (100, 53,

36 e 22% da luz solar plena); B) plântula em solo de Cerrado e C) em solo de Mata Atlântica. (Fotos: M. F. Goulart)

Experimentos in situ de longo prazo

Após a finalização dos experimentos em viveiro, os indivíduos foram

transplantados para três áreas, dando início a experimentos de longo prazo (Figura 4).

Alguns dos dados de sobrevivência destas plantas no campo integram o terceiro artigo

desta tese. Porém, de maneira geral, um maior tempo de acompanhamento é necessário

para que sejam alcançadas conclusões sobre a adaptação destes indivíduos em diferentes

condições de campo.

Figura 4. Indivíduo com 2,5 anos, crescendo em condições de campo. (Foto: M. F. Goulart)

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Estrutura da tese

Esta tese é composta por três capítulos redigidos em formato de artigo científico,

em inglês. Os três artigos contrastam a biologia de populações do vinhático de

diferentes biomas, Cerrado e Mata Atlântica, e de regiões ecotonais. O primeiro deles

tem como hipótese principal a existência de ecótipos de savana e floresta nesta espécie.

Esta hipótese foi confirmada com a avaliação do crescimento dos indivíduos ao longo

de seis meses iniciais. O segundo artigo dá ênfase na resposta morfológica e fisiológica

de indivíduos com seis meses de idade submetidos á diferentes tratamentos de luz. Este

artigo tem como hipótese principal a de que os diferentes ecótipos apresentam

diferenças nos níveis de plasticidade fenotípica em resposta a luz. O terceiro artigo

apresenta dados sobre a resposta dos indivíduos com seis meses de idade ao solo de

Mata Atlântica e ao solo de Cerrado. Novamente, respostas morfológicas, fisiológicas e

plasticidade fenotípica são avaliadas, bem como dados de sobrevivência dos indivíduos

em condições de campo. Este artigo tem como hipótese principal a de que os diferentes

ecótipos apresentam diferenças nos níveis de plasticidade fenotípica em resposta ao

solo. A abordagem de cada artigo está resumida na Tabela 1.

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Tabela 1. Resumo das abordagens dos três artigos que compõem esta tese.

Título dos artigos

Evidences for local adaptations from early developmental responses to light and soil fertility in the tropical tree

Plathymenia reticulata along a forest-savanna boundary

To which extent phenotypic plasticity in response to light

is involved in the ecotypic differentiation of a tree

species from savanna and forest habitats?

How important is soil fertility in driving

ecotypic differentiation of a tropical tree species

from savanna and forest habitats?

Dados analisados:

Morfológico não destrutivo

Morfológico destrutivo

Fotossíntese

Pigmentos foliares

Plasticidade fenotípica

Sobrevivência no campo

Idade dos indivíduos analisados:

de 1 a 7 meses (crescimento)

6 meses

32 meses*

Experimentos desenvolvidos:

Tratamentos de luz**

Tratamentos de solo**

Sobrevivência no campo

* indivíduos crescidos em viveiro por 12 meses e em condições de campo por 20 meses;

** experimento em viveiro

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Referências bibliográficas

Goulart MF. 2004. Variação morfológica e na fenologia de Plathymenia (Leguminosae-

Mimosoideae) em áreas de Cerrado, Mata Atlântica e de transição entre biomas, no estado

de Minas Gerais, Brasil. Dissertação de Mestrado. Universidade Federal de Minas Gerais.

Goulart MF, Lemos Filho JP, Lovato MB. 2005. Phenological variation within and among

populations of Plathymenia reticulata in Brazilian Cerrado, Atlantic Forest and transitional

sites. Annals of Botany 96: 445-455.

Goulart MF, Lemos Filho JP, Lovato MB. 2006. Variability in fruit and seed morphology

among and within populations of Plathymenia (Leguminosae - Mimosoideae) in areas of the

Cerrado, the Atlantic Forest, and transitional sites. Plant Biology 8: 112-119.

Heringer E P. 1956. O gênero Plathymenia. Anais da Sociedade Botânica do Brasil 7: 55-64

Lacerda DR, Acedo MDP, Lemos Filho JP, Lovato MB. 2002. Molecular differentiation of two

vicariant neotropical tree species, Plathymenia foliolosa and P. reticulata (Mimosoideae),

inferred using RAPD markers. Plant Systematic and Evolution 235: 67-77.

Poorter H, Garnier E. 2007. Ecological significance of inherent variation in relative growth rate

and its components. In: Functional Plant Ecology (Pugnaire FI, Valladares F, eds). CRC

Press – Taylor and Francis Group: New York.

Ridley M. 2004. Evolution. Blackwell Publishing: New York.

Silva Júnior MC. 2005. Cem árvores do Cerrado: guia de campo. Rede de sementes do Cerrado:

Brasília.

Valladares F, Martinéz-Ferri E, Balaguer L, Peréz-Corona E, Manrique E. 2000a. Low leaf-

level response to light and nutrients in Mediterranean evergreen oaks: a conservative

resource-use strategy? New Phytologist 148: 79-91.

Valladares F, Wright JS, Lasso E, Kitajima K, Pearcy RW. 2000b. Plastic phenotypic response

to light of 16 congeneric shrubs from a Panamanian rainforest. Ecology 81(7): 1925-1936.

Warwick MC, Lewis GP. 2003. Revision of Plathymenia (Leguminosae – Mimosoideae).

Edinburgh Journal of Botany 60: 111-119.

Westoby M. 2007. Generalization in functional plant ecology: the species-sampling problem,

plant ecology strategy schemes and phylogeny. In: Functional Plant Ecology (Pugnaire FI,

Valladares F, eds). CRC Press – Taylor and Francis Group: New York.

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CAPÍTULO 1:

Evidences for local adaptations from early developmental responses

to light and soil fertility in the tropical tree Plathymenia reticulata in a

forest-savanna boundary

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Introduction

Plant populations occurring in contrasting habitats may evolve in two different

ways: populations may specialize to a fraction of the environment or may generalize

some kind of adaptation to a broad range of the environment (Bazzaz 1996). The

specialization strategy is related to the selection of distinct, genetically-controlled

character states in different populations, giving rise to ecotypes (Nagy and Rice 1997).

Ecotypes are likely to be observed in species that colonize contrasting altitudinal,

moisture, salinity, light and nutrients habitats (Hogan 1996). In the tropics, boundaries

between forest and savanna vegetations may be characterized by adjacent contrasting

habitats concerning several of those environmental characteristics.

In tropical regions, forests usually dominate sites of greater nutrient and water

availability, while savannas are more associated to poor, deep and well drained soils,

seasonal climate and the effect of intermittent fires (Furley 1992, Haridasan 1992). For

plants in forest, light is the major limiting resource for growth, survival and

reproduction (Chazdon et al. 1996, Pearcy 2007), while at savannas, nutrient and water

are much more limiting (as reviewed by Jackson et al. 1999). Because of these major

environmental differences, forest and savanna plant species typically conform very

distinct functional types, differing in physiological, morphological and life history

attributes (Hoffmann et al. 2005).

In the present work we approached the microevolution of a tropical tree by

focusing on early-life adaptations of different populations to forest and savanna

environmental conditions. Considering that evolutionary changes begin with a shift of

gene frequencies in populations (Ridley 2004), the microevolution perspective is of

great importance to understand how populations evolve in forest and savanna ecotones.

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This issue is of great importance as boundaries between these vegetation types are

highly dynamic and, although under present climatic conditions forests are in a phase of

natural expansion over savannas, human activities, especially fires, are strongly

changing this process (Favier et al. 2004).

In South America, a corridor of xeric savanna vegetation runs between the two

main areas of moist tropical forest: the Amazonian Forest in the northwest and the

Atlantic Forest in the east and southeast (Oliveira-Filho and Ratter 2002). In central

Brazil, the corridor is dominated by the Cerrado biome which comprises widely varying

physiognomic types of vegetation that ranges from treeless grasslands to dense

woodlands. The most common physiognomy is named Cerrado sensu stricto (opposed

to Cerrado sensu lato, which is a generic term for all physiognomies of the biome) and

originally occupied more than 65% of the biome (Haridasan 1992). It is a xeromorphic

savanna characterized by a community of trees and shrubs, usually about 2-8 m in

height with contorted trunks, thick corky bark, sclerophyllous leaves and crown cover

of 10-60%, below which there is a well developed grassy ground layer (Ratter et al.

1997). The Cerrado forms an extent boundary with the Atlantic Forest biome, a typical

tropical forest, showing a more mesic environment. Although physiognomically very

different, the biomes may occur under the same latitude, under the same major climatic

condition and show some floristic similarity (Oliveira-Filho and Fontes 2000, Oliveira-

Filho and Ratter 2002).

In the present work we tested the hypothesis that the differentiation of ecotypes

adapted to forest or savanna conditions is involved in the colonization of Atlantic Forest

and Cerrado by a single species. Further, we hypothesized that the ecotypes should

show similar traits to those reported for forest and savanna species, although the

differences in traits across populations should be less contrasting than when comparing

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different species. We also hypothesized that populations from ecotonal areas between

forest and savanna should show traits similar to populations on their respective core

area.

In order to test the hypotheses, we assumed that earlier stages of life cycle are

the phases at which selective pressures are highest (Reich et al. 2003, Silvera et al.

2003). We predicted that habitat-based selection should lead to different set of traits in

seedlings and saplings from populations from different habitats. These hypotheses were

investigated in populations of the woody species Plathymenia reticulata (Leguminosae,

Mimosoideae) located in core sites of each biome and in ecotonal area between them.

Individuals were grown in a common garden and submitted to different light and soil

treatments mimicking the range of conditions experienced in the natural habitats.

Materials and methods

Studied tree species

Plathymenia reticulata, known as “vinhático”, can be commonly found in both

Cerrado and Atlantic Forest. Originally, the different populations were considered

vicariant species, P. reticulata and P. foliolosa, occurring respectively at Cerrado and

Atlantic Forest (Mendes and Paviani 1997). In 2002 the possibility of gene flow

between Plathymenia from Cerrado and Atlantic Forest was pointed out by a molecular

markers study (Lacerda et al. 2002). In the following year, a taxonomic revision of this

genus was made and only P. reticulata was recognized as taxonomic characters occur in

a continuum or there is no geographic correlation (Warwick and Lewis 2003). So far, no

ecotypes or any infra specific taxa is recognized for this species (Warwick and Lewis

2003).

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Studied populations, seeds collection and germination

We evaluated four populations of P. reticulata from Minas Gerais state,

southeast Brazil. Two populations are characterized as the Atlantic Forest semi-

deciduous physiognomy and in them individuals of P. reticulata reach 20 m in height.

The first population is located in the biome core area (19°45’S 43°31’W) and the other

one is located in its periphery, in an ecotone with the Cerrado (19°56’S 46°56’W). The

two other evaluated populations are in the Cerrado biome, both characterized as Cerrado

stricto sensu physiognomy and in them P. reticulata trees are shorter and tortuously

branched. One Cerrado population is located in the core area of the biome (18°43’S

45°03’W) and the other one in its periphery, in an ecotone with the Atlantic Forest

(19°49’S 43°48’W). The approximate location of each population are shown in Figure

1.

AmazoniaForest

Cerrado

Caatinga

AtlanticForest0 1000 Km Minas Gerais state

0 160 Km

Cerrado

Cerrado in ecotoneForest in ecotone

Forest

AmazoniaForest

Cerrado

Caatinga

AtlanticForest0 1000 Km Minas Gerais state

0 160 Km

Cerrado

Cerrado in ecotoneForest in ecotone

Forest

Figure 1. Brazil’s and Minas Gerais state’s main biomes, with the approximate

location of the studied populations of P. reticulata.

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Seeds were collected randomly as mixed samples from 10 individuals from each

population in September 2004. In late December 2004, seeds were submitted to

mechanical scarification and germination was conducted at 28oC in darkness as in

Lacerda et al. (2004). After six days of germination, seedlings were planted in pots and

placed in a nursery at a site characterized as ecotone between the two biomes (19°56’S

46°56’W). Most individuals were submitted to a non destructive experiment. By being

evaluated only by non destructive measurements, these individuals could be later

transferred to field conditions as part of a long term experiment. Fewer individuals were

submitted to a destructive experiment due to low seed number.

Non destructive experiment

A total of 120 seedlings from each one of four populations were planted in

numbered pots (18 cm of diameter and 32 cm of depth). Half of the pots were filled

with soil collected from Atlantic Forest and another half with soil from Cerrado.

Chemical analyses of soils are shown in Table 1 and revealed a higher organic matter

and nutrients content in soil from Atlantic Forest and higher levels of exchangeable

aluminium in Cerrado, a typical pattern found while comparing soil between these

biomes (Ruggiero et al. 2002).

Seedlings were equally and randomly arranged in four growing houses (1 x 8

m), each of them representing a different light environment: sun and three levels of

shade, produced with the use of layers of neutral shade cloth. The shade cloths were

supported by wood frames and stood 1 m above the tables and covered also its sides.

Measures of photosynthetic photon flux density were performed in three locations in

each house during a clear summer day, with quantum sensors (Licor, LI-189) at 30

minutes interval. These measures showed that the houses provided 50.3, 26.5, 18.2 and

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11.0 mol.m-2.day-1, respectively 100%, 53%, 36% and 22% of full sunlight. The blocks

were established to test for homogeneity of irradiance in each light treatment, however

analysis of variance (ANOVA) showed the block effect on the response variables

studied was not significant.

Table 1. Chemical analysis of soil samples collected in a Cerrado location and in a

Atlantic Forest, used as different soil treatments in the nursery experiment (V = base

saturation, m = aluminum saturation).

Soil treatments

Chemical parameters Cerrado Atlantic Forest

pH in water 5.2 5.6

Organic matter (g/Kg) 18.0 28.4

N (g/Kg) 1.0 1.4

C (g/Kg) 1.0 1.4

P (mg/Kg) < 1 2.2

K (mg/Kg) 48 128

Al 3+ (cmolc/Kg) 0.86 0.27

Ca 2+ (cmolc/Kg) 0.36 1.65

Mg 2+ (cmolc/Kg) 0.13 0.68

V% 17.01 44.01

m% 58.39 9.21

After 30 days of growth (late January 2005), each individual had the cotyledon

area estimated by doubling the multiplication of the maximum length and maximum

width of a single cotyledon. Cotyledon retention time was estimated by evaluating

presence or absence of cotyledon in each individual at 30, 60 and 90 days of growth.

Morphology of individuals was evaluated at 30 day interval during 7 months (from

January to July 2005). With the use of a digital paquimeter (0.01 mm precision) and

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common rule, plants total height (cm) and base diameter (mm) were measured and

slenderness index estimated as height / base diameter.

Destructive experiment

A total of 60 seedlings from each population were used, excluding Cerrado in

transition population due to low seed number. Seedlings were planted in numbered pots

(25 cm of diameter and 40 cm of depth), filled with 3:1 nutrient enriched peat and sand

mixture. Growth responses to two light treatments were evaluated during six months

(from January to June 2005). For each population, 30 seedlings were placed in full

sunlight growing house and the other 30 in 22% of full sunlight growing house.

At 30 day interval, five individuals from each population at each light treatment

were harvest. Seedlings were separated into leaves, stems and roots and dry mass of

each fraction was weighted after three days at 70oC. Leaf area was measured on a

flatbed scanner with computer software (Easy Quantify), before drying. We calculated

the total dry mass, shoot:root ratio (shoot dry mass / root dry mass), specific leaf area

(SLA = leaf area / leaf dry mass) and leaf area ratio (LAR = leaf area / total dry mass).

We also calculated monthly relative growth rate by the paring method (Hoffmann and

Poorter 2002) where 1212 /)]ln()[ln( ttMMRGR −−= being M1 and M2 plant dry

masses at times t1 and t2 and net assimilation rate as

)ln)(ln/()( 121212 AAttMMNAR +−−= being M1 and M2 plant dry masses and A1

and A2 leaf area and at times t1 and t2.

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Analysis of data

All data were logarithmically transformed and the assumptions of normality and

homoscedasticity were met. Concerning non-destructive experiment, one-way ANOVA

followed by post hoc Tukey test were made in order to compare cotyledon’s area among

P. reticulata populations. Comparisons of height and slenderness index among

populations were made for each combination of soil and light treatment separately.

Repeated measures ANOVAs were conducted using day of measure as within subject

variable (Potvin et al. 1990) followed by post hoc Tukey tests to rank populations

according to mean traits values at each survey.

For traits obtained in the destructive experiment, ANOVAs were conducted

considering as source of variance: population, light treatment, day of measure and the

interactions population x light, population x day, light x day and population x light x

day. For each trait, post hoc Tukey tests were made to rank populations being done

separately for each light treatment at each survey.

Results

The duration of the seedling phase (estimated by the maintenance of cotyledons)

differed among populations. Independently of light and soil treatments, individuals from

Atlantic Forest core and ecotone had already lost the cotyledons sixty days after

germination while the majority of the individuals from Cerrado core and ecotone only

lost the cotyledons one month later (Figure 1). The area of the cotyledon did not show

significant differences among populations (F=2.50; p=0.07).

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Figure 2. Percentage of individuals of P. reticulata from four different populations (Cerrado, Cerrado

in ecotone, Atlantic Forest in ecotone and Atlantic Forest) with cotyledons present at different ages.

Concerning non destructive evaluations, populations of P. reticulata showed

several differences on the initial growth phase. In relation to height, differences among

populations tended to increased over time in all light and soil treatments, especially

once cotyledons were lost. Atlantic Forest core population showed a tendency towards

higher values than Cerrado core and frequently populations from ecotonal region

showed intermediated values. Overall differences were stronger in plants submitted to

lower irradiance and to Atlantic Forest soil treatment. Under these conditions, in the last

survey, plants from Atlantic Forest core area showed almost three times the mean height

than individuals from Cerrado core population (Table 2 and Figure 3).

0

20

40

60

80

100

30 60 90

Days

% in

divi

dual

s with

cot

yled

ons

Cerrado Cerrado in ecotone

Forest in ecotone Forest

0

20

40

60

80

100

30 60 90

Days

% in

divi

dual

s with

cot

yled

ons

Cerrado Cerrado in ecotone

Forest in ecotone Forest

Slenderness indexes were always higher in Atlantic Forest core population when

compared to Cerrado, showing that individuals from Atlantic Forest have a tendency

towards investing proportionately more in height than in stem diameter. In similar way

to height, frequently, populations from ecotonal region showed intermediated values for

slenderness index, especially Atlantic Forest in ecotone. In a general way, the

slenderness indexes were higher in individuals submitted to lower irradiance treatments

and decreased overtime (Table 2 and Figure 4).

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Table 2. Analysis of variance of repeated measures of height and slenderness index recorded P. reticulata

from four populations (Cerrado, Cerrado in ecotone, Atlantic Forest in ecotone and Atlantic Forest)

submitted to different combinations of soil (soil from Cerrado and from Atlantic Forest) and light (100,

53, 36 and 22% of full sunlight) treatments. Day of measurement was considered as a repeated variable.

DF stands for degrees of freedom. Variance ratios (F values) are reported with associated level of

significance (* = p<0.05; ** = p<0.01; *** = p<0.001; ns = not significant).

Soil treatment Light treatment Source of variation DF Height Slenderness index

Cerrado 100% Population 3 4.72 * 10.76 ***

Day 6 46.75 *** 10.61 ***

Day x population 18 2.43 ** 1.78 *

Cerrado 53% Population 3 30.65 *** 54.22 ***

Day 5 73.17 *** 47.11 ***

Day x population 15 5.65 *** ns

Cerrado 36% Population 3 11.70 *** 37.53 ***

Day 6 28.60 *** 62.16 ***

Day x population 18 4.51 *** 2.02 **

Cerrado 22% Population 3 11.72 *** 37.53 ***

Day 6 91.84 *** 62.15 ***

Day x population 18 11.04 *** 2.02 **

Forest 100% Population 3 ns 13.02 **

Day 6 65.66 *** 13.30 ***

Day x population 18 2.54 ** ns

Forest 53% Population 3 7.15 *** 20.21 ***

Day 5 130.21 *** 80.18 ***

Day x population 15 4.00 *** 2.12 **

Forest 36% Population 3 3.16 * 6.53 **

Day 6 50.86 *** 17.92 ***

Day x population 18 3.16 *** ns

Forest 22% Population 3 12.00 *** 15.53 ***

Day 6 173.09 *** 68.71 ***

Day x population 18 18.77 *** 2.88 ***

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Figure 3. Mean values of height obtained in individuals of P. reticulata from four different populations

(Cerrado, Cerrado in ecotone, Atlantic Forest in ecotone and Atlantic Forest) during early phase of

growth. Individuals where submitted to different combinations of light treatments (100, 53, 36 and 22%

of full sunlight) and soil treatments (Cerrado soil and Atlantic Forest soil). At each time interval, letters

indicate significant comparisons among populations by Tukey test with p<0.05, alphabetical order

corresponds to ranking mean value and absence of letters indicates no significant differences among

populations.

0

4080

120160

200240

280320

360

30 60 90 120 150 180 210

Days

Hei

ght (

mm

)

0

4080

120

160200

240

280320

360

Hei

ght (

mm

)

0

40

80

120

160200

240

280

320

360

Hei

ght (

mm

)

0

40

80

120

160

200

240

280

320

360

Hei

ght (

mm

)

30 60 90 120 150 180 210

Days

Cerrado soil Atlantic Forest soil22

% o

fful

lsun

light

36%

off

ulls

unlig

ht53

% o

fful

lsun

light

100%

off

ulls

unlig

ht

a

bb

ab

Cerrado Cerrado in ecotone Forest in ecotone Forest

a

b

b

ab

aab

bb

a

ab

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ght (

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Cerrado soil Atlantic Forest soil22

% o

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Cerrado Cerrado in ecotone Forest in ecotone Forest

a

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0123456789

10

30 60 90 120 150 180 210

Days

0123456789

10

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10

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30 60 90 120 150 180 210

Days

Cerrado soil Atlantic Forest soil

fsu

n6

ull

light

% o

fsu

t10

n

Slen

dern

essi

ndex

(cm

.mm

-1)

Sl

ende

rnes

sind

ex(c

m.m

m -1

)

S

lend

erne

ssin

dex

(cm

.mm

-1)

Sle

nder

ness

inde

x(c

m.m

m -1

)

Figure 4. Mean values of slenderness indexes obtained in individuals of P. reticulata from four different

populations (Cerrado, Cerrado in ecotone, Atlantic Forest in ecotone and Atlantic Forest) during early

phase of growth. Individuals where submitted to different combinations of light treatments (100, 53, 36

and 22% of full sunlight) and soil treatments (Cerrado soil and Atlantic Forest soil). At each time interval,

letters indicate significant comparisons among populations by Tukey test with p<0.05, alphabetical order

corresponds to ranking mean value and absence of letters indicates no significant differences among

populations.

22%

ofu

lllig

ht3

% o

ffsu

n53

full

nlig

h0%

off

ulls

ulig

ht

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Cerrado Cerrado in ecotone Forest in ecotone Forest

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30 60 90 120 150 180 210

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Cerrado soil Atlantic Forest soil

fsu

n6

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light

% o

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dern

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(cm

.mm

-1)

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.mm

-1)

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Cerrado Cerrado in ecotone Forest in ecotone Forest

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light

full

su0%

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nlig

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ll53

sun

% o

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Concerning destructive evaluations, individuals’ dry mass increased over time

with higher values in plants submitted to full sunlight treatment. In the two final surveys

differences were found among populations with significant higher values in Atlantic

Forest core and ecotone. At the age of 210 days, plants from Atlantic Forest core area

showed around twice the mean dry mass than individuals from Cerrado, at both light

treatments (Table 3 and Figure 5).

Significant differences in shoot:root ratio were observed among populations in

plants submitted to shade treatment, while no significant differences were found among

populations in full sunlight treatment. Under shade, higher values of shoot:root were

found in Atlantic Forest core and ecotone, showing that individuals in these populations

allocated proportionately more mass in shoots than roots, in comparison to Cerrado

(Table 3 and Figure 5).

Concerning leaf area ratio and specific leaf area, a general tendency of a

decrease in values over time was observed, as well as of higher values in plants

submitted to shade. Comparisons among populations showed significant differences in

leaf area ratio at several ages at both light treatments, with higher values in Atlantic

Forest core and ecotone. No significant differences among populations in specific leaf

area were observed (Table 3 and Figure 4).

Relative growth rates showed a general tendency to increase overtime and no

significant differences between light treatments were observed. Comparisons among

populations showed that, most frequently, Atlantic Forest core and ecotone had higher

values for relative growth rates than Cerrado population. Net assimilation rate showed a

general tendency to increase overtime and significantly higher values were found in

plants submitted to full sunlight treatment. No significant differences among

populations were found (Table 3 and Figure 5).

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Figure 5. Mean values of shoot:root ratio, dry mass, leaf area ratio (LAR), specific leaf area (SLA),

obtained individuals of P. reticulata from three different populations (Cerrado, Atlantic Forest in ecotone

and Atlantic Forest) during early phase of growth. Individuals where submitted to two light treatments

(100 and 22% of full sunlight). At each time interval, letters indicate significant comparisons among

populations by Tukey test with alphabetical order corresponding to ranking mean value and absence of

letters indicating no significant differences among populations.

02468

1012

Dry

mas

s (g)

aabb

a

ab

b

aab

b

a

a

b

0

100

200

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30 60 90 120 150 180

SLA

(cm

2 . g

-1)

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100150200250300

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(cm

2 .g -1

)

Days Days

100% of full sunlight 22% of full sunlight

aab

b

aa

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a

b

b

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Cerrado Forest in ecotone Forest

01234567

Shoo

t:roo

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io

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02468

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mas

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aab

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Cerrado Forest in ecotone Forest

01234567

Shoo

t:roo

t rat

io

aab

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c

b

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35

-0.01

0.00

0.01

0.02

0.03

0.04

1 2 3 4 5

th -1

)

Figure 6. Mean values of relative growth rates (RGR) and net assimilation rates (NAR) obtained individuals of

P. reticulata from three different populations (Cerrado, Forest in ecotone and Forest) during early phase of

growth. Individuals where submitted to two light treatments (100 and 22% of full sunlight). At each time

interval, letters indicate significant comparisons among populations by Tukey test with alphabetical order

corresponding to ranking mean value and absence of letters indicating no significant differences among

populations.

Table 3. Analysis of variance of dry mass, shoot:root ratio, specific leaf area (SLA), leaf area ratio (LAR),

relative growth rate (RGR) and net assimilation rate (NAR) recorded on P. reticulata from three different

populations (Cerrado, Atlantic Forest in ecotone and Atlantic Forest) and submitted to two light treatments

(100 and 22% of full sunlight). DF stands for degrees of freedom. Variance ratios (F values) are reported with

associated level of significance (* = p<0.05; ** = p<0.01; *** = p<0.001; ns = not significant).

Source of variation DF Dry mass Shoot:root SLA LAR DF RGR NAR

Population 2 8.45*** 10.65*** ns 15.42*** 2 5.71** ns

Light treatment 1 26.87*** ns 47.20*** 10.41*** 1 ns 29.16***

Day of measure 5 65.78*** 16.72*** 15.92*** 30.71*** 4 33.83*** 21.51***

Population*light 2 ns ns ns ns 2 3.62* ns

Population*day 10 3.38*** ns ns 2.67** 8 12.40*** 4.34**

Light*day 5 14.15*** ns ns ns 4 16.53*** 11.34***

Population*light*day 10 ns ns ns ns 8 9.34*** 3.08**

NA

R (g

.on

cm2 .m

1 2 3 4 5

-1.0

0.0

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RGR

(g.g

.mon

th -1

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60 90 120 150 180 60 90 120 150 180

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100% of full sunlight 22% of full sunlight

a

b

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Cerrado Forest in ecotone Forest

-0.01

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(g.

onth

-1)

cm2 .m

NA

R

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.mon

th -1

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60 90 120 150 180 60 90 120 150 180

Days Days

100% of full sunlight 22% of full sunlight

a

b

a

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bb

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c

b

a

b

a

b

b

a

aa b

Cerrado Forest in ecotone Forest

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Discussion

Differences among populations

Individuals from all populations invested in growing taller by elongating stems

when exposed to shade, a known shade escape response related to the shade avoidance

syndrome (Ballaré et al. 1997, Smith and Whitelan 1997, Kurepin et al. 2006). These

shade responses, however, were much more evident in Atlantic Forest than in Cerrado

populations. In general, forest habitats are more limited by light than by any other

resource (Chazdon et al. 1996, Pearcy 2007) and our results show that Atlantic Forest

populations of P. reticulata are more adapted to cope with it than the Cerrado

populations.

Among populations of P. reticulata, no significant differences were observed in

SLA although higher LAR was found in Atlantic Forest. While comparing congeneric

species of Cerrado and Forests, Hoffman and Franco (2003) reported a general tendency

of higher values of SLA and LAR in species from Forests. Some authors have pointed

to higher values of SLA and LAR in shade plants as a strategy to maximize light

capture (Poorter 1999). On the other hand, at Cerrado, lower values may be

advantageous as plants from dryer habitats reduce the transpiration surface area and

minimize the water loss by reducing SLA and LAR (Dudley 1996, Gonzalez-Astorga et

al. 2003, Silvera et al. 2003).

During the early phase of growth, individuals acquire most of necessary

resources from seed reserves, being seedling mass highly dependent on seed mass and

less on external resource availability (Kitajima 1996). Individuals from different

populations of P. reticulata have similar quantities of seed reserve as there are no

significant differences among populations concerning seed mass (Goulart et al. 2006) or

cotyledons area (present study). Individuals from Atlantic Forest, however, consumed

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37

the reserves faster, showing a lower retention time of cotyledons. In spite of the faster

reserve consumption, plants from Atlantic Forest populations did not significantly

outgrew Cerrado ones at early age, during seedling phase. Significantly higher mass

accumulation in plants from Atlantic Forest populations were only observed after 150

days of growth.

Higher biomass accumulation and higher relative growth rate in individuals from

Atlantic Forest core and ecotone could be related to a higher competitive ability in these

populations when compared to Cerrado. Higher growth rates in individuals from

Atlantic Forest may be advantageous by promoting quick occupation of the available

space within the crowded vegetation (Poorter and Garnier 2007). While at Cerrado,

lower growth is related to stress resistant syndrome, typical of plants specialist to low-

resource environment (Chapin et al. 1993).

Besides lower growth rate, lower shoot:root ratio was another characteristic

exhibited by P. reticulata from Cerrado that is frequently related to stress resistant

syndrome (Chapin et al. 1993). Differences in shoot:root ratio has been considered the

most striking difference between Cerrado and Atlantic Forest species (Hoffmann and

Franco 2003). Higher investment in aerial growth in Atlantic Forest plants should be

related to shade avoidance while greater investment in roots in Cerrado plants is

interpreted as a strategy to capture nutrient and water (Hoffmann and Franco 2003).

Ecotypic differentiation

The differences found among populations of P. reticulata from Atlantic Forest,

Cerrado and ecotonal region in individuals growing in our common garden experiment

suggest the existence of genetically based differences among these populations. As

discussed above, these differences occur in an adaptive direction, suggesting that natural

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38

selection is an important force promoting genetic divergences between the populations.

This leads us to suggest that there are different ecotypes from Cerrado and Atlantic

Forest in this species. The main differences among ecotypes are related to differences in

the shade avoidance syndrome and the competitive ability, two features that are more

expressed in the forest ecotype with the savanna ecotype being more characterized by

stress resistance traits.

This ecotypic differentiation could lead to niche partitioning among populations

(Schuler 1996). In nursery conditions, the savanna ecotype was able to grow under light

and soil conditions that simulate the real forest habitats. However, at natural conditions,

the savanna ecotype would probably be less successful in Atlantic Forest, since it is a

weaker competitor in a highly competitive environment. In spite of its higher

competitive ability, the forest ecotype would not perform well in Cerrado areas due to

its apparently limited capacity to tolerate stressful conditions. One possible advantage

of the stress resistance syndrome in Cerrado is that by growing slow, plants can

accumulate sugar and nutrients during favorable times, enabling them to grow when

resources are less available (Poorter and Garnier 2007). Indeed, the need to invest in

storage is observed in trees from Cerrado, which commonly invest in root carbohydrate

necessary for resprout after fire (Hoffmann et al. 2003).

Evolutionary trends in savanna-forest boundary

At the boundary between the biomes the populations showed intermediate values

for several studied traits. Considering that the studied boundary is characterized by a

mosaic of adjacent patches of Cerrado and Atlantic Forest physiognomically very

similar to their respective core habitat, it is not likely that the ecotone populations are

ecotypes adapted to intermediate environmental conditions. Alternatively, it is more

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likely that the ecotone populations are characterized by hybrid individuals between

ecotypes. Hybridization is possible since there is similar flowering period between

populations (Goulart et al. 2005), moreover, evidence of gene flow has being pointed by

Lacerda et al. (2002) based on data from neutral genetic markers.

It is noteworthy that the putative hybrids, in spite of showing intermediate values

for several traits, are more similar to their respective core area ecotype than to the other

habitat ecotype. This pattern was also observed concerning phenological behavior

(Goulart et al. 2005) and fruit and seed morphology and dispersal potential (Goulart et

al. 2006) in this species. These differences can be taken as a suggestion for a strong

habitat-based selection in the patches of Atlantic Forest and Cerrado located in the

boundary between this biomes. In spite of the presence of gene flow among the

populations, natural selection act keeping adaptive differences at each patch.

Ecotypic differentiation is often envisioned as an early stage in the process of

speciation by adaptive radiation, which leads to a latter proliferation of species

accompanied by divergence in the kinds of resources exploited and the morphological

and physiological traits used to exploit the resources (Schuler 1996). Selection pressures

that remove hybrids are important in the speciation process (Schuler 1996) and when

ecotypes are highly dissimilar, hybrids can suffer negative selection due to outbreeding

depression (Hufford and Mazer 2003). Further investigation related to ecotypes survival

and reproduction is necessary to better understand evolutionary trends in this system,

however, the present work show no evidence of selection against possible hybrids

between ecotypes during early developmental phases.

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References

Ballaré CL, Scopel AL, Sanchez RA. 1997. Foraging for light: photosensory ecology and

agricultural implications. Plant, Cell and Environment 20: 820-825.

Bazzaz FA. 1996. Plants in changing environments: linking physiological, population and

community ecology. Cambridge University Press: Cambridge.

Chapin FS, Autumn K, Pugnaire F. 1993. Evolution of suites of traits in response to

environmental stress. American Naturalist 142: 78-92.

Chazdon RL, Pearcy RW, Lee DW, Fetcher N. 1996. Photosynthetic responses of tropical forest

plants to contrasting light environments. In: Tropical forest plant ecophysiology (Mulkey

SS, Chazdon RL, Simth AP, eds). Chapman & Hall: New York.

Dudley SA. 1996. The response to differing selection on plant physiological traits: evidence for

local adaptation. Evolution 50: 103-110.

Favier C, Chave J, Fabing A, Schwartz D, Dubois MA. 2004. Modeling forest-savanna mosaic

dynamics in man-influenced environments: effects of fire, climate and soil heterogeneity.

Ecological Modelling 171: 85-102.

Furley PA. 1992. Edaphic changes at the forest-savanna boundary with particular reference to

the neotropics. In: Nature and dynamics of forest-savanna boundaries (Furley PA, Proctor J,

Ratter JA, eds). Chapman & Hall: London.

González-Astorga J, Vovides AP, Iglesias C. 2003. Morphological and geographic variation of

the cycad Dioon edule Lindl. (Zamiaceae): ecological and evolutionary implications.

Botanical Journal of the Linnean Society 141: 465-470.

Goulart MF, Lemos Filho JP, Lovato MB. 2005. Phenological variation within and among

populations of Plathymenia reticulata in Brazilian Cerrado, Atlantic Forest and transitional

sites. Annals of Botany 96: 445-455.

Goulart MF, Lemos Filho JP, Lovato MB. 2006. Variability in fruit and seed morphology

among and within populations of Plathymenia (Leguminosae - Mimosoideae) in areas of the

Cerrado, the Atlantic Forest, and transitional sites. Plant Biology 8: 112-119.

Haridasan M. 1992. Observations on soils, foliar nutrient concentrations and floristic

composition of cerrado sensu stricto and cerradão communities in central Brazil. In: Nature

Page 41: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

41

and dynamics of forest-savanna boundaries (Furley PA, Proctor J, Ratter JA, eds). Chapman

& Hall: London.

Hoffmann WA, Poorter H. 2002. Avoiding bias in calculations of relative growth rate. Annals

of Botany 80: 37-42.

Hoffmann WA, Franco AC. 2003. Comparative growth analysis of tropical forest and savanna

woody plants using phylogenetically independent contrasts. Journal of Ecology 91: 475-

484.

Hoffmann WA, Orthen B, Nascimento PKV. 2003. Comparative fire ecology of tropical

savanna and forest trees. Functional Ecology 17: 720-726.

Hoffmann WA, Franco AC, Moreira MZ, Haridasan M. 2005. Specific leaf area explains

differences in leaf traits between congeneric savanna and forest trees. Functional Ecology

19: 932-940.

Hogan KP. 1996. Ecotypic variation in the physiology of tropical plants. In: Tropical forest

plant ecophysiology (Mulkey SS, Chazdon RL, Simth AP, eds). Chapman & Hall: New

York.

Hufford KM, Mazer SJ. 2003. Plant ecotypes: genetic differentiation in the age of ecological

restoration. Trends in Ecology and Evolution 18: 147-155.

Jackson PC, Meinzer FC, Bustamante M, Goldstein G, Franco A, Rundel PW, Caldas L, Igler E,

Causin F. 1999. Partitioning of soil water among tree species in a Brazilian Cerrado

ecosystem. Tree Physiology 19: 717-724.

Kitajima K. 1996. Ecophysiology of tropical tree seedlings. In: Tropical forest plant

ecophysiology (Mulkey SS, Chazdon RL, Simth AP, eds). Chapman & Hall: New York.

Kurepin LV, Walton LJ, Reid DM, Pharis RP, Chinnappa CC. 2006. Growth and ethylene

evolution by shade and sun ecotypes of Stellaria longipes in response to varied light quality

and irradiance. Plant, Cell and Environment 29: 647-652.

Lacerda DR, Acedo MDP, Lemos Filho JP, Lovato MB. 2002. Molecular differentiation of two

vicariant neotropical tree species, Plathymenia foliolosa and P. reticulata (Mimosoideae),

inferred using RAPD markers. Plant Systematic and Evolution 235: 67-77.

Lacerda DR, Lemos Filho JP, Goulart MF, Ribeiro RA, Lovato MB. 2004. Seed dormancy

variation in natural populations of two tropical leguminous tree species: Senna multijuga

Page 42: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

42

(Caesalpinoideae) and Plathymenia reticulata (Mimosoideae). Seed Science Research 14:

127-135.

Mendes IC, Paviani TI. 1997. Morfo-anatomia comparada das folhas do par vicariante

Plathymenia foliolosa Benth. e Plathymenia reticulata Benth. (Leguminosae-

Mimosoideae). Revista Brasileira de Botânica 20: 185-195.

Nagy ES, Rice KJ. 1997. Local adaptation in two subspecies of an annual plant: implications for

migration and gene flow. Evolution 51: 1079-1089.

Oliveira-Filho AT, Fontes MA. 2000. Patterns of floristic differentiation among Atlantic Forests

in Southeastern Brazil and the influence of climate. Biotropica 32: 793-810.

Oliveira-Filho AT, Ratter JA. 2002. Vegetation physiognomies and woody flora of the Cerrado

biome. In: The Cerrados of Brazil: ecology and natural history of a neotropical savanna

(Oliveira PS, Marquis RJ, eds). Columbia University Press: New York.

Pearcy RW. 2007. Responses of plants to heterogeneous light environments. In: Functional

Plant Ecology (Pugnaire FI, Valladares F, eds). CRC Press – Taylor and Francis Group:

New York.

Poorter H, Garnier E. 2007. Ecological significance of inherent variation in relative growth rate

and its components. In: Functional Plant Ecology (Pugnaire FI, Valladares F, eds). CRC

Press – Taylor and Francis Group: New York.

Poorter L. 1999. Growth response of 15 rain-forest tree species to a light gradient: the relative

importance of morphological and physiological traits. Functional Ecology 13: 396-410.

Potvin C, Lechowicz MJ, Tardif S. 1990. The statistical analysis of ecophysiological response

curves obtained from experiments involving repeated measures. Ecology 71: 1389-1400.

Ratter JA, Ribeiro JF, Bridgewater S. 1997. The Brazilian Cerrado vegetation and threats to its

biodiversity. Annals of Botany 80: 223-230.

Reich PB, Wright IJ, Cavender-Bares J, Craine JM, Oleksyn J, Westoby KM, Walters MB.

2003. The evolution of plant functional variation: traits, spectra and strategies. International

Journal of Plant Science 164: 143-164.

Ridley M. 2004. Evolution. Blackwell Publishing: New York.

Ruggiero PGC, Batalha MA, Pivello VR, Meirelles ST. 2002. Soil-vegetation relationships in

cerrado (Brazilian savanna) and semidecidous forest, Southeastern Brazil. Plant Ecology

160: 1-16.

Page 43: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

43

Schuler D. 1996. Ecological causes of adaptive radiation. American Naturalist 148: S40-S64.

Silvera K, Skillman JB, Dalling JW. 2003. Seed germination, seedling growth and habitat

partitioning in two morphotypes of the tropical pioneer tree Trema micrantha in a seasonal

forest in Panama. Journal of Tropical Ecology 19: 27-34.

Smith H, Whitelan GC. 1997. The shade avoindance syndrome: multiple responses mediated by

multiple phytochromes. Plant, Cell and Environment 20: 840-844.

Warwick MC, Lewis GP. 2003. Revision of Plathymenia (Leguminosae - Mimosoideae).

Edinburgh Journal of Botany 60: 111-119.

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CAPÍTULO 2:

To which extent phenotypic plasticity in response to light

is involved in the ecotypic differentiation of a tree species from

savanna and forest habitats?

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Introduction

Tropical environments include the most diverse plant communities on earth due

to a complexity of biotic and abiotic factors (Givnish 1999, Wright 2002). Among these

factors, spatial and temporal heterogeneity of light has been pointed as an important

mechanism to enable species coexistence, being related to niche partitioning among

plants (Poorter and Arets 2003, Balderrama and Chazdon 2005). Although less studied

and understood with this perspective, phenotypic plasticity in response to light could

also be important for the increase and maintenance of plant diversity (Valladares et al.

2000b). This may seem paradoxical since phenotypic plasticity enables a given

genotype to occupy different environments, so it is usually considered as a retarding

factor of evolutionary change (West-Eberhard 1989). However, plasticity can be a

diversifying factor in evolution since it is in itself a trait subject to natural selection and

can be the result of specialization to a fraction of the environmental heterogeneity

(West-Eberhard 1989, Lortie and Aarssen 1996, Valladares et al. 2000b, Ghalambor et

al. 2007).

Among the most biodiverse ecoregions in the world are the tropical Brazilian

Atlantic Forest and the Brazilian Cerrado, both considered priority hot spots for

conservation (Myers et al. 2000). The Brazilian Atlantic Forest is a typical tropical

forest with dense canopy and comparatively more mesic environmental conditions,

while the Cerrado biome ranges from grassland to woodland, typically being a

xeromorphic savanna named Cerrado sensu stricto. The Cerrado sensu stricto is

characterized by a community of trees and shrubs with a crown cover of 10-60% and a

well developed herbaceous layer (Ratter et al. 1997, Oliveira-Filho and Ratter 2002).

Although occurring in adjacent areas, the Atlantic Forest usually dominates sites of

greater nutrient and water availabilities, while the Cerrado biome is associated to poor,

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deep and well drained soils (Furley 1992, Haridasan 1992). However, this major pattern

is not always clear and vegetation and soil are so intimately related that it is difficult to

identify cause and effect relationships (Ruggiero et al. 2002, Hoffmann et al. 2005).

From a plant perspective, light is the environmental factor that differ the most

between Atlantic Forest and Cerrado habitats. In the Atlantic Forest the leaf area index

(LAI) is around 5 (Paula and Lemos Filho 2001) and light is the most limiting resource

for plant growth, survival and reproduction (Chazdon et al. 1996). At Cerrado, LAI

values are around 1, with light being highly available in the understory (Miranda et al.

1997). Besides light intensity, Atlantic Forest and Cerrado also differ in light

heterogeneity. Although Cerrado is heterogeneous in light (Moreira 2000), in Atlantic

Forest light varies to a larger extent both spatially and temporally. At forests, light

environments range from deeply shaded understories to full sunlight tree fall gaps and

light variation among microsites may be 50-fold (Niiments 2007). Besides, forest

understories are highly dynamic environments with temporal dynamics spanning from

years (e.g. canopy opening by tree fall) to seconds, since the very low background

understory irradiation is randomly punctuated by short duration but very bright

sunflecks (Pearcy 2007).

Environmental differences in light availability have led to specific and

contrasting adaptations in species from Atlantic Forest and Cerrado (Hoffmann and

Franco 2003). In a previous work, we demonstrated that adaptations to each ecosystem

also occur at a microevolutionary scale, with significant differences among populations

within the same species (Chapter 1). This was studied in the woody species

Plathymenia reticulata (Leguminosae - Mimosoideae), which form distinct ecotypes

adapted to Atlantic Forest and Cerrado, developing traits related to the shade avoidance

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syndrome and an enhanced competitive ability in the first and traits conferring stress

tolerance in the second (Chapter 1).

In this work we further investigate local adaptation in P. reticulata populations

hypothesizing that phenotypic plasticity in morphological and physiological traits in

response to light is involved in ecotypic differentiation in this species. We predicted that

Atlantic Forest ecotype should show higher phenotypic plasticity than the Cerrado

ecotype as an evolutionary response to the higher light heterogeneity experienced by

plants in the former ecosystem.

Material and methods

Studied populations

We evaluated four populations of P. reticulata from Minas Gerais state,

southeast Brazil, from which seeds were collected randomly as mixed samples from 10

individuals in September 2004. Two populations are characterized as the Atlantic Forest

semi-deciduous physiognomy being the first located in the biome core area (19°45’S

43°31’W) and the other one in its periphery, in an ecotonal area with the Cerrado

(19°56’S 46°56’W). The two other evaluated populations are in the Cerrado biome,

both characterized as Cerrado sensu stricto. One population is located in the core area of

the biome (18°43’S 45°03’W) and the other one in its periphery, in an ecotonal area

with the Atlantic Forest (19°49’S 43°48’W). Ecotones are environmentally very similar

to their respective core habitat, however, as there are some distinctive traits in

populations of P. reticulata located in ecotones (Lacerda et al. 2002, Goulart et al.

2005, Goulart et al. 2006, Chapter 1), they were here evaluated separately from core

areas. Populations characteristics are more detailed described in Chapter 1.

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Experimental design

In late December 2004, seeds were submitted to mechanical scarification and

germination was conducted at 28oC in darkness as in Lacerda et al. (2004). After six

days of germination, seedlings were planted in a nursery and were submitted to either

non-destructive or destructive experiment.

In the non-destructive experiment a total of 120 seedlings from each population

were planted in numbered pots (18 cm of diameter and 32 cm of depth) filled with soil

collected in a Atlantic Forest site (pH=5.6; N=1.4 mg/kg; P=2.2 mg/kg; K=128 mg/kg;

Ca2+=1.65 cmolc/kg; Mg2+=0.68 cmolc/kg). Seedlings were equally and randomly

arranged in four growing houses (1 x 8 m), each of them representing a different light

environment: sun and three levels of shade, produced with the use of layers of neutral

shade cloth. The shade cloths were supported by wood frames and stood 1 m above the

tables and covered also its sides. Measures of temperature, relative humidity and

photosynthetic photon flux density were performed in three locations in each house

during an entire sunny summer day at 30-minutes interval. These measures showed that

the houses environment’ differed mainly in irradiance, providing 100%, 53%, 36% and

22% of full sunlight (Table 1). At each house, three blocks were established to test for

homogeneity of irradiance, however they showed no significant effect on the evaluated

traits.

For the destructive experiment, 20 individuals from each population, excluding

the Cerrado in ecotone due to low seed number, were planted in numbered pots (25 cm

of diameter and 40 cm of depth) filled with 3:1 nutrient-enriched peat and sand mixture.

Seedlings were equally and randomly arranged in the growing houses that provided

100% and 22% of full sunlight.

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Table 1. Environmental conditions in the four growing houses, representing four different light

treatments. Data obtained in sunny summer day for every 30 minutes record, from 7 am to 6 pm. PPFD

stands for photosynthetic photon flux density.

Light treatments (percentage of full sunlight) Environmental variable

100 53 36 22

Daily PPFD (mol.m-2.day-1) 50.3 26.5 18.2 11.0

Maximum PPDF (µmol.m-2.s-1) 2521.0 1249.8 907.6 554.9

Mean PPDF (µmol.m-2.s-1) 1075.7 550.8 375.8 234.0

Minimum PPFD (µmol.m-2.s-1) 42.3 23.3 13.4 7.5

Maximum temperature (oC) 36.1 34.4 35.5 34.5

Mean temperature (oC) 31.5 31.3 31.3 30.3

Minimum temperature (oC) 19.6 19.2 19.2 19.3

Maximum relative humidity (%) 92.7 91.7 93.0 94.1

Mean relative humidity (%) 50.2 50.9 55.3 57.1

Minimum relative humidity (%) 31.5 30.5 36.2 41.3

Morphological and physiological measurements

Individuals in the non-destructive experiment were evaluated after six months of

growth, in June 2005. With the use of a digital paquimeter (0.01 mm precision) and

common ruler, height (cm) and base diameter (mm) were obtained and number of

internodes counted. Mean internode length (cm) was estimated as height / number of

intenodes, considering only individuals with a single bud, and slenderness index

(cm/mm) as height / base diameter.

Half of the individuals in the destructive experiment were harvested after one

month of growth (in January 2005) and the other half after six months of growth (June

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2005). Plants were separated into leaves, stems and roots, dry mass of each fraction was

weighted after three days at 70oC. Leaf area was measured on a flatbed scanner with

computer software (Easy Quantify), before drying. The following measurements were

calculated for six month seedlings: total dry mass, shoot:root ratio (shoot dry mass / root

dry mass), specific leaf area (SLA = leaf area / leaf dry biomass) and leaf area ratio

(LAR = leaf area / total dry biomass). We also calculated the relative growth rate by the

paring method (Hoffmann and Poorter 2002) where 1212 /)]ln()[ln( ttMMRGR −−=

being M1 and M2 plant dry masses at times t1 (1 month) and t2 (6 months) and net

assimilation rate as )ln)(ln/()( 121212 AAttMMNAR +−−= being M1 and M2 plant

dry masses and A1 and A2 leaf area and at times t1 and t2 .

In vivo chlorophyll fluorescence traits were evaluated in six six-month-old

individuals from each population growing at full sunlight and also at 22% of full

sunlight treatments. Measurements were made with the use of a pulse amplitude

modulated photosynthesis yield analyzer (Mini-PAM, Walz, Germany). Potential

quantum yield of photosystem II was calculated as: mmmv FFFFF /)(/ 0−= where Fm

and F0 are the maximum and the minimum fluorescence respectively, measured in fully

developed leaves after 30 minutes of dark adaptation. Light saturation curves were

obtained using the light curve program of the instrument, and used to determinate

maximum apparent photosynthetic electron transport rate (ETRmax) and saturating

photosynthetically active photon flux density (PPFDsat), following Rascher et al.

(2000). Leaf pigments content were determined in the same individuals by grounding

leaf samples in 80% acetone. Absorbance in the supernatant was measured

spectrophotometrically at 470, 646 and 663 nm and pigment contents were determined

using equations described in Lichtenthaler and Wellburn (1983).

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Analysis of data

In order to compare light treatments and populations, data were logarithmically

transformed and the assumptions of normality and homoscedasticity were met. Analyses

of variance (ANOVAs) considered as sources of variance light treatment, population

and also population x light treatment interaction. Whenever a factor did not show

significance, it was removed from the model and a new analysis was conducted. Post

hoc Tukey mean comparison tests were performed for population and for light

treatments, for all morphological and physiological traits.

For each population, plasticity was quantified under 22% and 100% of full

sunlight treatments, using the Relative Distance Phenotypic Index (RDPI) described by

Valladares et al. (2006). The relative distances (RD) among trait values for all pairs of

individuals of a given habitat grown in different light environment were determined as

, where j and j’ are individuals belonging to different

light environments i and i’. The RDPI ranges from 0 (no plasticity) to 1 (maximum

plasticity) and is obtained as

)/('' '''' ijjiijjiij xxjidRD +→=→

nxxjidRDPI ijjiij /))/(''( '' +→= ∑ where n is the total

number of RD. Comparisons of RDPIs among populations were made by ANOVAs and

post hoc Tukey test, or by Kruscal-Wallis and post hoc Holm test when non

parametrical distributions were found.

Results

A significant population x light treatment interaction was found for plant height

(Table 2). Height of plants in Cerrado core and in the ecotonal populations did not

significantly respond to the light treatments, while the Atlantic Forest core population

exhibited significant differences among light treatments, with plants in the darkest

shade treatment twice as taller as the ones in the full sunlight treatment (Figure 1A).

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Plants from Atlantic Forest core and ecotone showed significantly higher height than

Cerrado core and ecotone. Differences were greatest in the darkest shade treatment,

where plants from Atlantic Forest core grew almost three times taller than plants from

the Cerrado core population (Figure 1A).

Table 2. Analyses of variance for morphological and physiological characters recorded in P. reticulata

from four populations and submitted to two or four light treatments. Variance ratios (F values) are

reported with associated level of significance (* = p<0.05; ** = p<0.01; ns = not significant).

Sources of variance Traits

Population Light treatment Population x light

Height (cm) 25.00 ** 3.12 * 2.28 *

Slenderness Index (cm.mm-1) 43.96 *** 7.99 *** ns

Internodes length (cm) 16.33 *** ns ns

Dry mass (g) 5.4 * 7.89 * ns

Shoot:root ratio 14.06 *** ns 5.57 *

SLA (cm2.g-1) ns 32.61 *** ns

LAR (cm2.g-1) ns 21.18 ** ns

RGR (g.g.month-1) 10.74 *** ns 4.79 *

NAR (g.cm2.month-1) ns 19.60 ** 4.91 **

Fv/Fm ns ns ns

ETRmax ns ns ns

PPFDsat ns ns ns

Chlorophylls (µm.mg-1) ns 57.88 *** ns

Carotenoids:chlorophylls ratio 8.53 *** 10.42 ** ns

Chlorophyll a:b ratio ns ns ns

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0

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20

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30

35

40

Hei

ght (

cm)

100% 53% 36% 22%

Cerrado ForestForest in ecotone

Cerrado in ecotone

b ab a a

b ab ab b a ab ab ab c b bc b b a a

A)

0

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35

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Hei

ght (

cm)

100% 53% 36% 22%

Cerrado ForestForest in ecotone

Cerrado in ecotone

b ab a a

b ab ab b a ab ab ab c b bc b b a a

A)

0.00.51.01.52.02.53.03.54.04.5

1 2 3 4 5 6 7 8 9 10

Slen

dern

ess i

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(cm

.mm

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nght

(cm

)

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ess i

ndex

(cm

.mm

-1)

0.0

0.5

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e le

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(cm

)

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rado

in e

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ne

Cer

rado

22%

36%

53%

100%

c c b a

b b ab a

b b a a

B)

Figure 1. Means ± standard error of morphological non-destructive traits obtained in six months saplings of P. reticulata from four populations (Cerrado, Cerrado in transition, Atlantic Forest in transition and Atlantic Forest) grown under four different light levels (100, 53, 36 and 22% of full sunlight). In A) there is significant population x light treatment interaction, letters inside bars indicate differences among populations within each light treatment while letters above bars indicate differences among light treatment within each population. In B) there is no significant population x light treatment interaction, letters above white bars indicate comparisons among population while letters above black bars indicate comparisons among light treatments. Alphabetical order of letters corresponds with ranking mean value and absence of letters indicates no significant differences considering 95% confidence interval.

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No significant population x light treatment interaction was found for slenderness

index and internode length (Table 2). Populations significantly differed in slenderness

index and internode length with individuals from Atlantic Forest core showing mean

values almost twice as those from Cerrado core, while ecotonal populations showed

intermediate mean values (Figure 1B). Plants from all populations responded to light

treatments by significantly increasing the slenderness index in the shade, although not

by elongating the internodes since no differences were found among light treatments for

internode length (Figure 1B).

Dry mass, SLA and LAR did not show significant population x light treatment

interaction (Table 2). Populations significantly differed in dry mass but not in SLA and

LAR. Atlantic Forest core and ecotone individuals accumulated more than two times the

dry biomass accumulated by Cerrado ones (Figure 2B). Plants from all populations

showed significantly higher dry mass in full sunlight and significantly higher SLA and

LAR under shade (Figure 2B).

Shoot:root ratio, RGR and NAR showed significant population x light treatment

interaction (Table 2). Among the three evaluated populations, only Atlantic Forest core

showed significant differences in shoot:root ratio among light treatments. In this

population, plants growing in the shade showed mean shoot:root ratio two times bigger

than plants in full sunlight. No significant differences among populations were found in

the full sunlight treatment, while in the shade treatment, the Atlantic Forest core

population showed a significantly higher shoot:root ratio (Figure 2A). Significant

differences between light treatments in RGR were only found for Atlantic Forest

individuals, with higher mean values in full sunlight treatment. Comparisons among

populations showed higher RGR in Atlantic Forest core and ecotone at both light

treatments (Figure 2A). No significant differences among populations were found for

NAR, which significantly differed among light treatments for Cerrado and Atlantic

Forest core populations. In these populations individuals growing in full sunlight

showed higher NAR than those growing in shade (Figure 2A).

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Figure 2. Means ± standard error of morphological destructive traits obtained in six months saplings of P.

reticulata from three populations (Cerrado, Atlantic Forest in transition and Atlantic Forest) grown under

two different light levels (100 and 22% of full sunlight). In A) there is significant population x light

treatment interaction, letters inside bars indicate differences among population within each light treatment

while asterisk indicate differences between light treatment within each population. In B) there is no

significant population x light treatment, letters above white bars indicate comparisons among populations

while asterisks above black bars indicate comparisons among light treatments. Alphabetical order of

letters corresponds with ranking mean value and absence of letters or asterisks indicates no significant

differences considering 95% confidence interval.

0

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Dry

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0

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g)

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No significant population x light treatment interaction was found for

photosynthetic traits and leaf pigment content (Table 2). For photosynthetic traits

(Fv/Fm, ETRmax, PPFDsat), differences among populations and differences among

light treatments were not significant (Table 2 and Figure 3A). For leaf pigment content,

only carotenoids:chlorophyll ratio showed significant differences among populations,

with higher mean values in Cerrado core and ecotone. Comparison between light

treatments showed significant differences for chlorophyll content and

carotenoids:chlorophyll ratio, but not to chlorophyll a:b ratio. Individuals growing in the

shade showed significantly higher chlorophyll and lower carotenoids:chlorophyll ratio

than those growing in full sunlight (Table 2 and Figure 3B).

Phenotypic plasticity in response to light was comparatively higher for dry mass,

NAR, SLA, LAR and chlorophyll content (final mean RDPI ranging from 0.28 to 0.41).

Intermediate plasticity was found for height, slenderness index, root:shoot ratio,

ETRmax and PPFDsat (final mean RDPI between 0.17 and 0.24). Traits as internode

length, RGR, Fv/Fm, carotenoids:chlorophyll ratio and chlorophyll a:b ratio showed to

be comparatively less plastic (final mean RPDI between 0.03 and 0.14). Comparisons of

phenotypic plasticity among populations rendered several significant differences. For

morphological traits (height, slenderness index, LAR and NAR) plasticity was higher in

Atlantic Forest core population, while for leaf pigments contents (chlorophyll,

carotenoids:chlorophyll ratio, chlorophyll a:b ratio), higher plasticity was found either

in Atlantic Forest core or both ecotonal populations. Traits such as internode length, dry

mass, shoot:root ratio, SLA, RGR and the ones related to photosynthetic response did

not show differences in plasticity among populations (Table 3).

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Figure 3. Means ± standard error of physiological traits obtained in six months saplings of P. reticulata

from four populations (Cerrado, Cerrado in transition, Atlantic Forest in transition and Atlantic Forest)

grown under two different light levels (100 and 22% of full sunlight). In A) traits related to

photosynthetic performance are present and in B) leaf pigments contents are presented. Letters above

white bars indicate comparisons among populations while asterisks above black bars indicate

comparisons among light treatments. Alphabetical order of letters corresponds with ranking mean value

and absence of letters or asterisks indicates no significant differences considering 95% confidence

interval.

0.5

6

7

8

9

1 2 3 4 5 6 7 8

Fv/F

m

0.

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2000

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Chlo

roph

ylls

(µg.

mg -1

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Cer

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in e

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m

0.

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2000

3000

4000

Chlo

roph

ylls

(µg.

mg -1

)

0.0

0.1

0.2

0.3

1 2 3 4 5 6 7 8

Caro

teno

ids:c

hlor

ophy

lls ra

tio

0102030405060708090

0

1 2 3 4 5 6 7 8

ETR

max

10

0

0

0

0

0

0

0

0

0

PPFD

sat

80

70

60

50

40

30

20

10

0

1

2

3

4

Chlo

roph

yll a

:b ra

tio

Fore

st

Fore

st in

eco

tone

Cer

rado

in e

coto

ne

Cer

rado

22%

100%

a ab c bc

*

*

Fore

st in

eco

tone

Cer

rado

in e

coto

ne

Cer

rado

22%

100%

Fore

st

A) B)

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Table 2. Plasticity indexes (RDPI) of morphological and physiological traits obtained in of P. reticulata

from four populations. Characters marked with “np” are non parametric, medians are presented and

compared by Kruskal Wallis (Chi-square value) and post hoc Holm test, for the others, means are

presented and compared by ANOVA (F values) and post hoc Tukey test. Levels of significance are * =

p<0.05; ** = p<0.01; *** = p<0.001; ns = not significant and alphabetical order of letters correspond with

ranking mean or median value.

Traits Cerrado Cerrado in

ecotone

Forest in

ecotone Forest F Ch-sq

Height np 0.17 b 0.16 b 0.15 b 0.29 a - 86.69 ***

Slenderness index np 0.11 c 0.20 b 0.22 a 0.21 ab - 56.62 ***

Internode length np 0.14 0.14 0.10 0.13 - ns

Dry mass 0.45 0.32 0.45 ns -

Shoot:root 0.21 0.21 0.29 ns -

SLA 0.33 0.21 0.31 ns -

LAR 0.23 b 0.22 b 0.42 a 9.62 *** -

RGR np 0.10 0.06 0.10 - ns

NAR 0.27 b 0.24 b 0.44 a 6.26 ** -

Fv/Fm np 0.03 0.03 0.02 0.02 - ns

ETRmax np 0.13 0.18 0.21 0.14 - ns

PPFDsat 0.18 0.17 0.20 0.19 ns -

Chlorophyll 0.26 b 0.35 b 0.52 a 0.30 b 10.49*** -

Carotenoids:chlorophyll np 0.10 b 0.17 a 0.17 a 0.11 b - 15.70 **

Chlorophyll a:b 0.08 b 0.13 a 0.16 a 0.12 a - 9.67 *

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Discussion

Phenotypic plasticity in response to light

Comparative studies that evaluate phenotypic plasticity among functional plant

groups are important in determining the implications of plasticity for the distribution,

spread and persistence of populations, and also for understanding patterns of

evolutionary diversification (Sultan 2000). In the past few years, the accumulated

knowledge about plastic responses of plants to the light environment suggested the

existence of the general trend of higher plasticity in sun-adapted versus shade-tolerant

plant species (Valladares et al. 2000a, Grime and Mackey 2002, Valladares et al. 2005).

The trend may depend, however, on the traits analyzed since sun plants seems to be

more plastic for physiological features while plasticity for morphological and

architectural traits seems to be greater in shade plants (Valladares et al. 2002, Niinemets

and Valladares 2004, Valladares et al. 2007).

Ecotypic differentiation towards lower plasticity in populations from more

homogeneous light environment was reported by Balaguer et al. (2001) in a comparison

of Mediterranean oak populations from habitats with different levels of light

heterogeneity. The results of the present work point to a similar pattern for P. reticulata

populations, with lower values for plasticity indexes in Cerrado core compared to the

other populations. Significantly higher plasticity in morphological traits (height,

slenderness index, LAR and NAR) was found in Atlantic Forest core, while for leaf

pigments contents, significantly higher plasticity was found in Atlantic Forest core and

both ecotonal populations.

These results can be interpreted as habitat based selection for plasticity. Higher

morphological plasticity in response to light in Atlantic Forest saplings suggests higher

efficiency in exploiting this limiting resource than plants from Cerrado. Morphological

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plasticity has been linked to an enhanced capacity to survive and grow in the understory

(Valladares et al. 2000b) as a particular mechanism to optimize resource acquisition in

plants (West-Eberhard 1989). The evolutionary advantage and the benefits of plasticity

are better understood than its disadvantages, limits and costs (DeWitt et al. 1998), but a

reduced plasticity can be advantageous under stressful conditions where a conservative

resource use is crucial (Valladares et al. 2007). In this context, lower plasticity in

response to light in Cerrado saplings may be one more feature related to the stress

resistance syndrome (Chapin et al. 1993). The lower plasticity could prevent Cerrado

plants under a temporally favorable circumstance to grow too large or to produce

structures that are too expensive to be sustained once conditions deteriorate, as has been

discussed for evergreen woody plants in both tropical and Mediterranean ecosystems

(Valladares et al. 2000a, b).

Hoffmann and Franco’s (2003) explored macroevolutionary processes across

Cerrado and Forests by comparing congeneric pairs of savanna and forest plant species.

These authors concluded that plasticity was higher in Cerrado species, although

exceptions were reported. Considering that many Cerrado species occur in several

microhabitats within the Cerrado, from grasslands to woodlands, higher plasticity in

some Cerrado species is likely to be explained at least in part by the fact that these

species occur over a wider range of environmental conditions and not because savanna

in Cerrado is more heterogeneous with regards to light than forests as argued by

Hoffmann and Franco (2003). In fact, evidences that plants occurring over a wider

range of light environments show higher plasticity in response to light than the ones that

occur over a narrower range has already being reported by Popma et al. (1992). Thus,

the apparent contradictory results found here can be reconciled with those of Hoffmann

and Franco (2003) by considering that their results show rather similar levels of

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plasticity in Cerrado vs Forests species and by realizing the different level of analysis,

micro vs. macroevolutionary, i.e. populations vs species. Our study suggests that the

ecotypic differentiation of the populations of P. reticulata involves differentiation not

only in certain functional traits but also in the plasticity of these traits to gradients of

light availability leading to an overall more conservative resource use strategy in

Cerrado than in Atlantic Forest populations.

Functional heterogeneity of the light environment

The light environment tends to be more homogeneous in open habitats while

forest understories are highly variable regarding light availability both in time and in

space (Örgren and Sundin 1996). The observed environmental heterogeneity, however,

does not always match the heterogeneity really experienced by organisms, which are

named structural and functional heterogeneity, respectively (Li and Reynolds 1995,

Gómez et al. 2004). In order to test the hypothesis that phenotypic plasticity is higher in

habitat with more heterogeneous light environment, we assumed that functional light

heterogeneity experienced by P. reticulata saplings in Atlantic Forest was higher than

that in Cerrado. Our assumption, however, disagree with that of Hoffmann and Franco

(2003) since they assumed a greater light heterogeneity in savannas from Cerrado than

in Forests. Without a specific determination of the functional light heterogeneity

experienced by seedlings and saplings in each of these habitats, the hypotheses of both

the present work and those by Hoffmann and Franco (2003) can be proposed. However,

in support to our assumption, it is unlikely that saplings from Cerrado experience a

greater gradient in light resource than those in the Forests, since the very low levels of

light availability observed in the Forests are never found in the Cerrado while both

ecosystems have zones of similarly high levels of irradiance. Thus, further investigation

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is needed to better understand light as ecological and evolutionary factor in these

ecosystems and to better interpret micro and macroevolutionary processes in the

Cerrado-Atlantic Forest boundary. It is important to bear in mind that plastic responses

to light of species and populations are not only explained by the heterogeneity of the

light environment experienced in each case but also by a complexity of co-occurring

biotic and abiotic factors, which can set important limits to the expression of plasticity

(Valladares et al. 2007).

Functional traits and ecotypic differentiation

Besides showing ecotypic differentiation in phenotypic plasticity, the results of

this work also indicates ecotypic differentiation in functional traits, reinforcing the

findings of Chapter 1 and bringing new evidences. Concerning morphological traits,

more evident shade avoidance syndrome and competitive ability in Atlantic Forest and

stress resistance traits in Cerrado was reported.

For leaf pigment content, the results reinforce the notion that irradiance directly

affects composition and concentration of pigments (Rosevear et al. 2001). Individuals

submitted to shade improved light interception by showing higher chlorophyll

concentration (Johnson et al. 1997) while the ones submitted to sun maximized

photoprotection by showing higher carotenoids:chlorophyll ratio (Demmig-Adams and

Adams 1992). The results also show a genetic determination on pigment features since

the savanna ecotype showed higher carotenoids:chlorophyll ratio than the forest

ecotype.

Concerning photosynthesis traits, we expected that Atlantic Forest individuals to

show higher levels of photoinhibition as shade plants have a decreased capacity to

dissipate excess light energy (Reich et al. 2003). We also expected the Cerrado

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individuals to show higher light saturation levels for photosynthesis, according to

common features of sun-adapted plants (Bazzaz 1979). In this work, however, no

significant differences between light treatments nor between populations in

photosynthetic traits were observed. This agrees with Nicotra et al. (1997) who reported

that physiological traits related to photosynthetic performance are under strong

stabilizing pressure and may show little or no variation among genotypes.

References

Balaguer L, Martinéz-Ferri E, Valladares F, Pérez-Corona ME, Baquedano FJ, Castillo FJ,

Marinque E. 2001. Population divergence in the plasticity of the response of Quercus

coccifera to the light environment. Functional Ecology 15: 124-135.

Balderrama SIV, Chazdon RL. 2005. Light-dependent seedling survival and growth of four tree

species in Costa Rican second-growth rain forests. Journal of Tropical Ecology 21: 383-

395.

Bazzaz FA. 1979. The physiological ecology of plant succession. Annual Review of Ecology

and Systematics 10: 351-371.

Chapin FS, Autumn K, Pugnaire F. 1993. Evolution of suites of traits in response to

environmental stress. American Naturalist 142: 78-92.

Chazdon RL, Pearcy RW, Lee DW, Fetcher N. 1996. Photosynthetic responses of tropical forest

plants to contrasting light environments. In: Tropical forest plant ecophysiology (Mulkey

SS, Chazdon RL, Simth AP, eds). Chapman & Hall: New York.

Demmig-Adams B, Adams WW. 1992. Photoprotection and other responses of plants to high

light stress. Annual Review Plant Physiology and Plant Molecular Biology 43: 599-626.

DeWitt T, Sih A, Wilson DS. 1998. Costs and limits of phenotypic plasticity. Trends in Ecology

and Evolution 13(2): 77-81.

Furley PA. 1992. Edaphic changes at the forest-savanna boundary with particular reference to

the neotropics. In: Nature and dynamics of forest-savanna boundaries (Furley PA, Proctor J,

Ratter JA, eds). Chapman & Hall: London.

Page 64: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

64

Ghalambor CK, MacKay JK, Carroll SP, Reznick DN. 2007. Adaptive versus non-adaptive

phenotypic plasticity and the potential for contemporary adaptation in new environments.

Functional Ecology 21: 349-407.

Givnish TJ. 1999. On the causes of gradients in tropical tree diversity. Journal of Ecology 87:

193-210.

Goméz JM, Valladares F, Puerta-Piñero C. 2004. Differences between structural and functional

environmental heterogeneity caused by seed dispersal. Functional Ecology 18: 787-792.

Goulart MF, Lemos Filho JP, Lovato MB. 2005. Phenological variation within and among

populations of Plathymenia reticulata in Brazilian Cerrado, Atlantic Forest and transitional

sites. Annals of Botany 96: 445-455.

Goulart MF, Lemos Filho JP, Lovato MB. 2006. Variability in fruit and seed morphology

among and within populations of Plathymenia (Leguminosae - Mimosoideae) in areas of the

Cerrado, the Atlantic Forest, and transitional sites. Plant Biology 8: 112-119.

Grime JP, Mackey JML. 2002. The role of plasticity in resource capture by plants. Evolutionary

Ecology 16: 299-307.

Haridasan M. 1992. Observations on soils, foliar nutrient concentrations and floristic

composition of cerrado sensu stricto and cerradão communities in central Brazil. In: Nature

and dynamics of forest-savanna boundaries (Furley PA, Proctor J, Ratter JA, eds). Chapman

& Hall: London.

Hoffmann WA, Poorter H. 2002. Avoiding bias in calculations of relative growth rate. Annals

of Botany 80: 37-42.

Hoffmann WA, Franco AC. 2003. Comparative growth analysis of tropical forest and savanna

woody plants using phylogenetically independent contrasts. Journal of Ecology 91: 475-

484.

Hoffmann WA, Franco AC, Moreira MZ, Haridasan M. 2005. Specific leaf area explains

differences in leaf traits between congeneric savanna and forest trees. Functional Ecology

19: 932-940.

Johnson JD, Tognetti R, Michelozzi M, Pinzauti S, Minotta G, Borghetti M. 1997.

Ecophysiological responses of Fagus sylvatica seedlings to changing light conditions. II.

The interaction of light environment and soil fertility on seedling physiology. Physiologia

Plantarum 101(1): 24-134.

Page 65: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

65

Kurepin LV, Walton LJ, Reid DM, Pharis RP, Chinnappa CC. 2006. Growth and ethylene

evolution by shade and sun ecotypes of Stellaria longipes in response to varied light quality

and irradiance. Plant, Cell and Environment 29: 647-652.

Lacerda DR, Acedo MDP, Lemos Filho JP, Lovato MB. 2002. Molecular differentiation of two

vicariant neotropical tree species, Plathymenia foliolosa and P. reticulata (Mimosoideae),

inferred using RAPD markers. Plant Systematic and Evolution 235: 67-77.

Lacerda DR, Lemos Filho JP, Goulart MF, Ribeiro RA, Lovato MB. 2004. Seed dormancy

variation in natural populations of two tropical leguminous tree species: Senna multijuga

(Caesalpinoideae) and Plathymenia reticulata (Mimosoideae). Seed Science Research 14:

127-135.

Li H, Reynolds JF. 1995. On definition and quantification of heterogeneity. Oikos 73(2): 280-

284.

Lichtenthaler HK, Wellburn AR. 1983. Determination of total caroteoids and chlorophylls a and

b of leaf extract in different solvents. Biochemical Society Transactions 11: 591-592.

Lortie CJ, Aarssen LW. 1996. The specialization hypothesis for phenotypic plasticity in plants.

International Journal of Plant Sciences 157: 484-487.

Miranda AC, Miranda HS, Lloyd J, Grace J, Francey RJ, McIntyre JA, Meir P, Tiggan P,

Lockwood R, Brass J. 1997. Fluxes of carbon, water and energy over Brazilian cerrado: an

analysis using eddy covariance and stable isotopes. Plant, Cell and Environment 20:315-

328.

Moreira A. 2000. Effects of fire protection on savanna structure in Central Brazil. Journal of

Biogeography 27: 1021-1029.

Myers N, Mittermeier RA, Mittermeier CG, Fonseca GAB, Kent J. 2000. Biodiversity hotspots

for conservation priorities. Nature 403: 853-858.

Nicotra BA, Chazdon RL, Schlichting CD. 1997. Patterns of genotypic variation and phenotypic

plasticity of light response in two tropical Piper (Piperaceae) species. American Journal of

Botany 84:1542-1552.

Niiments U. 2007. Photosynthesis and resource distribution through plant canopies. Plant, Cell

and Environment 30: 1052-1071.

Page 66: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

66

Niinemets U, Valladares F. 2004. Photosynthetic acclimation to simultaneous and interacting

environmental stresses along natural light gradients: optimality and constraints. Plant

Biology 6: 254-268.

Oliveira-Filho AT, Ratter JA. 2002. Vegetation physiognomies and woody flora of the Cerrado

biome. In: The Cerrados of Brazil: ecology and natural history of a neotropical savanna

(Oliveira PS, Marquis RJ, eds). Columbia University Press: New York.

Örgren E, Sundin U. 1996. Photosynthetic responses to variable light: a comparison of species

from contrasting habitats. Oecologia: 106: 18-27.

Paula SA, Lemos Filho JP. 2001. Dinâmica do dossel em mata semidecídua do perímetro

urbano de Belo Horizonte, MG. Revista Brasileira de Botânica 24: 545-551.

Pearcy RW. 2007. Responses of plants to heterogeneous light environments. In: Functional

Plant Ecology (Pugnaire FI, Valladares F, eds). CRC Press – Taylor and Francis Group:

New York.

Poorter L, Arets EJMM. 2003. Light environment and tree strategies in a Bolivian tropical moist

forest: an evaluation of the light partitioning hypothesis. Plant Ecology 166: 295-306.

Popma J, Bongers F, Werger MJA. 1992. Gap-dependence and leaf characteristics of trees in a

tropical lowland rain forest in Mexico. Oikos 63: 207-214.

Rascher U, Liebig M, Luttge U. 2000. Evaluation of instant light-response curves of chlorophyll

fluorescence parameters obtained with portable chlorophyll fluorometer on site in the filed.

Plant, Cell and Environment 23: 1397-1405.

Ratter JA, Ribeiro JF, Bridgewater S. 1997. The Brazilian Cerrado vegetation and threats to its

biodiversity. Annals of Botany 80: 223-230.

Reich PB, Wright IJ, Cavender-Bares J, Craine JM, Oleksyn J, Westoby KM, Walters MB.

2003. The evolution of plant functional variation: traits, spectra and strategies. International

Journal of Plant Science 164: 143-164.

Rosevear MJ, Young AJ, Johnson GN. 2001. Growth condition are more important than species

origin in determining leaf pigment content of British plant species. Functional Ecology 15:

474-480.

Ruggiero PGC, Batalha MA, Pivello VR, Meirelles ST. 2002. Soil-vegetation relationships in

cerrado (Brazilian savanna) and semidecidous forest, Southeastern Brazil. Plant Ecology

160: 1-16.

Page 67: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

67

Sultan, SE. 2000. Phenotypic plasticity for plant development, function and life history. Trends

in Plant Science 5(12): 537-542.

Valladares F, Martinéz-Ferri E, Balaguer L, Peréz-Corona E, Manrique E. 2000a. Low leaf-

level response to light and nutrients in Mediterranean evergreen oaks: a conservative

resource-use strategy? New Phytologist 148: 79-91.

Valladares F, Wright JS, Lasso E, Kitajima K, Pearcy RW. 2000b. Plastic phenotypic response

to light of 16 congeneric shrubs from a Panamanian rainforest. Ecology 81(7): 1925-1936.

Valladares F, Chico JM, Aranda I, Balaguer L, Dizengremel P, Manrique E, Dreyer E. 2002.

Greater high light seedling tolerance of Quercus robur over Fagus sylvatica is linked to a

greater physiological plasticity. Trees, Structure and Function 16: 395-403.

Valladares F, Arrieta S, Aranda I, Lorenzo D, Sánchez-Gómez D, Tena D, Suaréz F, Pardos JA.

2005. Shade tolerance, photoinhibition sensitivity and phenotypic plasticity of Ilex

aquifolium in continental Mediterranean sites. Tree Physiology 25: 1041-1052.

Valladares F, Sanchez-Gomez D, Zavala MA. 2006. Quantitative estimation of phenotypic

plasticity: bridging the gap between the evolutionary concept and its ecological

applications. Journal of Ecology 94: 1103-1116.

Valladares F, Gianoli E, Gómez JM. 2007. Ecological limits to plant phenotypic plasticity. New

Phytologist 176: 749-763.

West-Eberhard MJ. 1989. Phenotypic plasticity and the origins of diversity. Annual Review of

Ecology and Systematic 20: 249-278.

Wright JS. 2002. Plant diversity in tropical forests: a review of mechanisms of species

coexistence. Oecologia 130: 1-14.

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CAPÍTULO 3:

How important is soil fertility in driving ecotypic differentiation of a

tropical tree species from savanna and forest habitats?

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Introduction

All over the world, plant communities’ diversity, structure and biomass are

severely affected by soil characteristics such as hydrological status, texture, nutrient

availability and also biotic elements as root feeders, symbionts and decomposer

organisms (as reviewed by Lawrence 2003, Baltzer and Thomas 2005, Wijesinghe et al.

2005). Although such edaphic characteristics may vary considerably at local and

temporal scales, especially in tropical environments (Sultan and Bazzaz 1993, Baraloto

et al. 2006), there is much evidence of plant specialization to soil properties (Baltzer

and Thomas 2005). So, in a general way, soil characteristics are thought to be important

selective agents in plant evolution (Baraloto et al. 2006, Macel et al. 2007).

In the tropics, soil plays an important role in forest and savanna distributions,

with the first one usually correlating with higher water and nutrients availability (Furley

1992, Haridasan 1992). However, this major pattern is not always clear and vegetation

and soil are so intimately related that it is difficult to identify cause-and-effect

relationships (Ruggiero et al. 2002, Hoffmann et al. 2005). In Brazil, the Atlantic Forest

and the Cerrado provide a good model of study of plant specialization to soil conditions

as these are adjacent forest and savanna habitats with distinct major soil characteristics.

The Atlantic Forest originally covered more than 1 million km2, being a vast and

diversified biome with different physiognomies found along rainfall, temperature,

altitude, longitude and also soil gradients (Oliveira-Filho and Fontes 2000, Oliveira-

Fillho and Ratter 2002, Resende et al. 2002). Although soil characteristics strongly vary

along the Atlantic Forest biome (Resende et al. 2002), in general nutrient is much less

limiting than in Cerrado. The Cerrado biome once covered about 2 million km2 of

central Brazil, being constituted by xeromorphic vegetation that varies from grassland

to woodlands. The most typical Cerrado physiognomy is a savanna vegetation named

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Cerrado sensu stricto characterized by a community of trees and shrubs with crown

cover of 10-60% and a well developed grassy ground layer (Ratter et al. 1997, Oliveira-

Filho and Ratter 2002). Cerrado sensu stricto is generally found in poor and deep soils,

usually also characterized as acid, well-drained and with high levels of exchangeable

aluminum (Oliveira-Filho et al. 1989, Haridasan 1992, Ruggiero et al. 2002).

Plants from Atlantic Forest and Cerrado are considered different functional

groups as they show different physiological and life history attributes (Hoffmann et al.

2005). There are evidences of habitat specialization in the earlier phases of growth

between them, mainly related to growth and survival in response to vegetation cover

(Hoffmann and Franco 2003, Hoffmann et al. 2004) and to fire incidence (Hoffmann

and Moreira 2002). Concerning specialization to soil properties, little is known about

differences in the nutrients requirements between them (Hoffmann et al. 2005), but as

nutrients are more limited resource at Cerrado than at Atlantic Forest, some level of soil

specialization in plants is expected.

The leguminous tree species Plathymenia reticulata (Mimosoideae) provides a

good model to evaluate soil specialization as it can be found both at Atlantic Forest and

Cerrado habitats. A previous study suggested that the wide distribution of this species is

related to the existence of ecotypes adapted to different light and soil environments

(Chapter 1). In the present study, we further investigate populations’ responses to soil

and explore the extent of this environmental factor in driving ecotypic differentiation in

P. reticulata. Specifically, we tested the hypothesis that individuals are locally adapted,

showing morphological and physiological traits that enhance performance in their home

habitat soil condition. Moreover, we hypothesized that the locally adapted

characteristics should be shown even by individuals growing in a different soil

condition from their home habitat. Our prediction for these hypotheses is that Atlantic

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Forest individuals should show traits adapted to a more fertile and competitive habitat,

while Cerrado individuals should show traits adapted to less fertile and more stressful

habitat. Further, we hypothesized that ecotypes should differ in levels of phenotypic

plasticity in response to soil. We expected to find higher plasticity in Atlantic Forest

individuals as it enhances competitive ability (Grime 2002) and lower plasticity in

Cerrado individuals, as it confers stress tolerance (Chapin et al. 1993).

Material and methods

Studied populations

We evaluated four populations of P. reticulata from Minas Gerais state,

southeast Brazil, from which seeds were collected randomly as mixed samples from 10

individuals in September 2004. Two populations are characterized as the Atlantic Forest

semi-deciduous physiognomy being the first located in the biome core area (19°45’S

43°31’W) and the other one is located in its periphery, in an ecotonal area with the

Cerrado (19°56’S 46°56’W). The two other evaluated populations are in the Cerrado

biome, both characterized as Cerrado sensu stricto. One population is located in the core

area of the biome (18°43’S 45°03’W) and the other one in its periphery, in an ecotonal

area with the Atlantic Forest (19°49’S 43°48’W). Populations’ characteristics are more

detailed described in Chapter 1.

Soil chemical properties were evaluated in all populations by randomly

collecting 10 soil samples at 0 to 20 cm of depth. Soil samples were analyzed at the

“Laboratório de Química Agropecuária” from the “Instituto Mineiro de Agropecuária”

and their properties are shown in Table 1.

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Table 1. Chemical analysis of soil from samples provided from the four studied populations of P.

reticulata (Cerrado, Cerrado in ecotone, Atlantic Forest in ecotone and Atlantic Forest) from the two

different soil treatments used in a nursery experiment (Cerrado and Atlantic Forest). V% stands for base

saturation and m% for aluminum saturation.

Populations Soil treatments Chemical parameters

Cerrado Cerrado in ecotone Forest in ecotone Forest Cerrado Forest

pH in water 5.0 4.5 5.2 4.15 5.2 5.6

Organic matter (g/Kg) 24.8 24.8 26.0 51.2 18.0 28.4

N (g/Kg) 1.2 1.2 1.3 2.4 1.0 1.4

C (g/Kg) 1.2 1.2 2.4 1.3 1.0 1.4

P (mg/Kg) < 1 < 1 < 1 5.3 < 1 2.2

K (mg/Kg) 93 26 44 46.5 48 128

Al 3+ (cmolc/Kg) 2.44 1.35 0.66 4.15 0.86 0.27

Ca 2+ (cmolc/Kg) 0.08 0.35 0.86 0.24 0.36 1.65

Mg 2+ (cmolc/Kg) 0.17 0.08 0.11 0.14 0.13 0.68

V% 4.72 8.13 20.74 3.11 17.01 44.01

m% 83.37 72.95 37.99 89.34 58.39 9.21

Nursery experiment and data collection

In late December 2004, seeds were submitted to mechanical scarification and

germination was conducted at 28oC in darkness as in Lacerda et al. (2004). After six

days of germination, 30 seedlings from each population were planted in pots (18 cm of

diameter and 32 cm of depth). Half of the pots were filled with soil collected at a

Cerrado site and the other half with soil from an Atlantic Forest site. Chemical analyses

of soils are shown in Table 1.

During six months (from January to June 2005), seedlings grew in a nursery that

provided about 11.0 mol.m-2.day-1, representing around 22% of full sunlight. Under this

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irradiance level, greater differences among populations of P. reticulata were reported in

a previous study (Chapter 1). After this period, morphological and physiological traits

were evaluated.

Morphological data were taken with the use of a digital paquimeter (0.01 mm

precision) and common ruler, height (cm), maximum diameter of the crown (cm) and

base diameter (mm) were obtained and number of internodes counted. Mean internode

length (cm) was estimated as height / number of intenodes, considering only individuals

with a single bud, and slenderness index as height (cm) / base diameter (mm).

In vivo chlorophyll fluorescence traits were evaluated in six individuals, with six

months, from each population and submitted to each soil treatmetn. Measurements were

made with the use of a pulse amplitude modulated photosynthesis yield analyser (Mini-

PAM, Walz, Germany). Potential quantum yield of photosystem II was calculated as:

where Fmmmv FFFFF /)(/ 0−= m and F0 are the maximun and the minimum

fluorescence respectively, measured in fully developed leaves after 30 minutes of dark

adaptation. Light saturation curves were obtained using the light curve program of the

instrument, and used to determinate maximum apparent photosynthetic electron

transport rate (ETRmax) and saturating photosynthetically active photon flux density

(PPFDsat), following Rascher et al. (2000). Leaf pigments content were determined in

the same individuals by grounding leaf samples in 80% acetone. Absorbance in the

supernatant was measured spectrophotometrically at 470, 646 and 663 nm and pigment

contents were determined using equations described in Lichtenthaler and Wellburn

(1983).

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Field experiment and survival censuses

After one year of growth in the nursery, individuals were transplanted into a

field experiment part of an experimental vegetation recovery project of Atlantic Forest.

After several years of land cleaning, the area is now characterized by an open field, the

soil is acid (pH=4.5), rich in organic matter (41.4 g/Kg), with low base saturation

(V%=4.09) and high aluminum saturation (m%=81.01).

In January 2006, twenty individuals from each four populations from each soil

treatment were transplanted, totaling 160 individuals. The individuals were randomly

positioned in the area, distant 3 meters from each other. They were transplanted to holes

of about 25 cm of diameter and 40 cm of depth. Individuals were numbered, and the

population provenance and nursery soil treatment were registered. Mortality censuses

were made after 6 months (July 2006) and after 20 months (September 2007).

Analysis of data

Comparisons among soil treatments and populations in the nursery experiment

were made after logarithm transformation of data. First, Analyses of variance

(ANOVA) were conducted with the sources of variance: soil treatment, population and

also the population x soil treatment interaction. However, as the interaction was not

significant for all evaluated traits, one-way ANOVAs were conducted for soil treatment

and population separately. Comparisons among populations were also made using post

hoc Tukey test.

For each population, plasticity was quantified using the Relative Distance

Phenotypic Index (RDPI) described by Valladares et al. (2006). The relative distances

(RD) among trait values for all pairs of individuals of a given population grown in

different soil treatment were determined as )/('' '''' ijjiijjiij xxjidRD +→=→ , where j and

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j’ are individuals belonging to different light environments i and i’. The RDPI ranges

from 0 (no plasticity) to 1 (maximum plasticity) and is obtained as

where n is the total number of RD. RDPIs showed

non-parametric distributions even after transformations, so comparisons among

populations were made then by Kruscal-Wallis and post hoc Holm test.

nxxjidRDPI ijjiij /))/(''( '' +→=∑

In the field experiment, differences in the survival among population and among

individuals from different soil treatments were estimated by the Kaplan-Meier product-

limit method. The chi-square test was used to test significant survival differences.

Results

Six months saplings growing in the nursery showed significant differences in

morphological traits among populations (Table 2). Independently of soil treatment,

Atlantic Forest core population had the highest values from all morphological traits.

Atlantic Forest core showed almost three times the mean height and crown diameter,

and approximately twice the slenderness index and internode length found in the

Cerrado core population. Populations from the ecotonal area showed a tendency towards

intermediate values for morphological traits. Concerning comparisons between soil

treatments, significant differences were found for height and crown diameter with the

higher mean values in the individuals from the forest soil treatment (Table 2 and Figure

1).

For photosynthesis traits, P. reticulata individuals showed mean Fv/Fm of 0.79

(± 0.01), mean ETRmax of 80.34 (± 2.78) and mean PPFDsat of 586.70 (± 55.03), no

significant differences were found among populations nor between soil treatments

(Table 2 and Figure 2). Measures of pigment content showed significant differences

among populations but not between soil treatments. Concerning comparisons among

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populations, a tendency towards higher chlorophyll content was found in Atlantic Forest

core and both ecotonal populations while compared to Cerrado core population. Higher

mean values for carotenoids:chlorophyll ratio was found in Cerrado core and Cerrado

ecotone, while for chlorophyll a:b, higher ratio was found Cerrado core, followed by

both ecotonal population and lower values in Atlantic Forest core (Figure 2).

Table 2. Analysis of variance of morphological and physiological traits recorded on P. reticulata from

four different populations and two soil treatments. Variance ratios (F values) are reported with associated

level of significance (* = p<0.05; ** = p<0.01; ***=p<0.001; ns = not significant).

Traits Comparisons among

populations

Comparisons between

soil treatments

Height (cm) 24.20 *** 14.53 **

Slenderness index (cm.mm-1) 53.70 *** ns

Diameter of crown (cm) 18.93 *** 9.04 **

Internode lenght (cm) 17.86 *** ns

Fv/Fm ns ns

ETRmax ns ns

PPFDsat ns ns

Chlorophylls (µm.mg-1) 4.11 * ns

Carotenoids: chlorophylls ratio 15.87 *** ns

Chlorophyll a:b ratio 4.09 * ns

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0

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d c b a *

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c b a a *

b b a a

Figure 1. Means ± standard error of morphological traits obtained in six months saplings of P. reticulata

from four different populations (Cerrado, Cerrado in ecotone, Atlantic Forest in ecotone and Atlantic

Forest) submitted to two soil treatments (Cerrado soil and Atlantic Forest soil). Letters above white bars

indicate comparisons among populations while asterisks above black bars indicate comparisons among

soil treatments. Alphabetical order of letters corresponds with ranking mean value. Absence of asterisks

indicates no significant differences considering 95% confidence interval.

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20

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100

120

ETR

max

60

Figure 2. Means ± standard error of photosynthesis traits (A) and leaf pigment content (B) obtained in six

months saplings of P. reticulata from four different populations (Cerrado, Cerrado in ecotone, Atlantic

Forest in ecotone and Atlantic Forest) submitted to two soil treatments (Cerrado soil and Atlantic Forest

soil). Letters above white bars indicate comparisons among populations, alphabetical order corresponds

with ranking mean value and absence of letters indicates no significant differences considering 95%

confidence interval. No significant differences between soil treatments were detected.

0

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Among the evaluated traits, comparatively higher plasticity in response to soil

was found for height and crown diameter (mean RDPI of 0.22 and 0.20 respectively).

Intermediate plasticity was found for slenderness index, internode length, ETRmax,

PPFDsat, chlorophyll content and chlorophyll a:b ratio (mean RDPI between 0.12 and

0.17). Comparatively lower plasticity was found for the traits Fv/Fm and

carotenoids:chlorophylls ratio (mean RDPI lower than 0.10). Comparisons of

phenotypic plasticity among populations showed significant differences in six over ten

evaluated traits. For height, higher plasticity was found in Atlantic Forest core

population. The traits: slenderness index, internode length, Fv/Fm and chlorophyll a:b

ratio, showed a major tendency of higher plasticity in ecotonal populations while

compared to core ones. For PPFDsat significantly higher plasticity was found in

Atlantic Forest in ecotone, followed by the core populations and lower values in

Cerrado in ecotone. No significant differences in plasticity among populations were

found for diameter of crown, ETRmax, chlorophyll content and carotenoids:chlorophyll

ratio (Table 3).

Concerning individuals transplanted to field conditions, the mortality censuses

showed that 36,48% of the plants died after 20 months in the field. There was no

significant difference in survival in individuals from different populations (Chi-

square=1.36; p=0.714) (Figure 3). Significant differences in survival were found in

individuals from different soil treatments (Z=-2.19; p=0.028) with higher mortality rate

in those from the Cerrado soil treatment (Figure 3).

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Table 3. Plasticity indexes (RDPI) of morphological and physiological traits obtained in of P. reticulata

from four populations. Medians are presented and compared by Kruskal Wallis (Chi-square value) and

post hoc Holm test. Levels of significance are * = p<0.05; ** = p<0.01; *** = p<0.001; ns = not

significant. Alphabetical order of letters corresponds with ranking median value.

Populations Traits

Cerrado Cerrado in ecotone Forest in ecotone Forest

Chi-square

Height 0.21 b 0.21 b 0.19 b 0.27 a 17.18 **

Slenderness index 0.13 b 0.16 a 0.16 a 0.12 b 17.32 **

Diameter of crown 0.26 0.20 0.17 0.18 ns

Internode length 0.12 b 0.17 a 0.16 ab 0.14 b 9.81 *

Fv/Fm 0.013 b 0.025 a 0.013 ab 0.021 ab 8.52 *

ETRmax 0.17 0.13 0.19 0.20 ns

PPFDsat 0.13 b 0.05 c 0.29 a 0.17 b 12.34 **

Chlorophylls 0.10 0.13 0.12 0.13 ns

Carotenoids: chlorophylls ratio 0.08 0.09 0.09 0.10 ns

Chlorophyll a:b ratio 0.06 c 0.25 a 0.14 b 0.14 b 9.65 *

.

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cer mat16 18 20 22 24 26 28 30 32 34

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CerradoCerrado in ecotoneForest in ecotoneForest

Cerrado soilForest soilCerrado soilForest soil

Figure 3. Cumulative survival over time in individuals planted in field. In A) individuals submitted to two

different soil treatments during the nursery experiment, with the ones in from the Atlantic Forest soil

treatment surviving significantly less than the ones submitted to Cerrado soil. In B) individuals from four

populations (Cerrado, Cerrado in ecotone, Atlantic Forest in ecotone and Atlantic Forest) with no

significant differences in survival among them. Analyses were performed with the Kaplan–Meier product

limit, considering 95% confidence interval.

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Discussion

Responses to soil

The results of the nursery experiment showed that, concerning morphological

traits, plants responded to the higher levels of nutrients and organic matter in the

Atlantic Forest soil treatment by showing significantly higher height and crown

diameter than plants submitted to Cerrado soil. For leaf pigment, we expected

chlorophyll content to be higher in plants submitted to Atlantic Forest soil treatment as

higher availability of nutrients, especially nitrogen and magnesium, is known to

correlate with an increase in chlorophyll content (Johnson et al. 1997, Dale and Causton

1992). Leaf pigments, however, were not influenced by soil treatments, in this species

these traits are more influenced by environmental light and by genes, as discussed on

the next topic. Also, photosynthesis performance was not significantly influenced by the

soil treatments, contraring the expectation that improvement on soil nitrogen levels

would have a positive effect on photosysten II efficiency and a reduction on

photoinhibition (higher Fv/Fm) (Field 1983, Johnson et al. 1997). Photosynthesis traits

are probably very stable in this species, showing low responsiveness to soil and light

environment (Chapter 2) and also being very conserved among populations. Our results

for populations of P. reticulata agree with Nicotra et al. (1997) reports that

photosynthesis traits usually show little or no variation among genotypes.

Habitat specialization

Common garden experiments are frequently used to test genotypic differences

between provenances, however it may be hard to distinguish between divergence caused

by drift or by natural selection (Hufford and Mazer 2003). In the present work, we

considered as evidence of natural selection and local adaptation the fact that Atlantic

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Forest individuals showed higher mean values for morphological traits while compared

to Cerrado ones and the differences in pigment content found among populations, as

those differences occurred in an adaptive direction.

Concerning morphological traits, higher mean values of height, crown diameter,

slenderness index and internode length in the Atlantic Forest core population when

compared to Cerrado, show higher competitive ability in the first. The competitive

ability should be a response to a crowded habitat, highly limited in light resource (see

Chapter 1) but it also can be considered a response to higher nutrient levels, as more

productive habitats show higher competition intensity (Grime 2002). On the contrary,

lower mean values of morphological traits in Cerrado individuals, specially the reduced

stature, are probably an adaptation for survival on infertile soils, as demonstrated for

several other species (Grime 2002). The results reinforce that P. reticulata from

Cerrado, independently of soil conditions, show more evident stress resistance traits

than Atlantic Forest’s. These traits should enable plants to accumulate more reserves of

nutrient elements in the infertile soil habitat (Chapin et al. 1993, Grime 2002),

increasing nutrient use efficiency (Reich et al. 1992).

Both Cerrado and Atlantic Forest habitats may show seasonal climate, although

the length and the severity of the dry season are more marked at Cerrado (Oliveira-

Fillho and Fontes 2000, Oliveira-Filho and Ratter 2002, Goulart et al. 2005). P.

reticulata individuals are adapted to the seasonal water deficit by showing deciduous

habit, losing leaves during drier months and avoiding transpiration water loss (Goulart

et al. 2005). Cerrado populations may show more evident adaptation to this seasonality

by showing reduced morphological traits, including stature and leaf area (Chapter 1),

which may enhance water use efficiency (Dudley 1996, Gonzalez-Astorga et al. 2003,

Silvera et al. 2003). The deciduous habit, however, is not usually found in species from

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nutrient poor habitat, on the contrary, evergreeness represent a lower tissue turnover

strategy that enhance nutrient economy in infertile soils (Chapin et al. 1993, Grime

2002). P. reticulata individuals probably overcome the nutrient deficit caused by leaf

loss by showing association with nitrogen fixing microorganism (Faria and Lima 1998).

The results of this study bring new evidences that reinforce the genetic

determination on pigment content in P. reticulata populations. Under similar

environmental conditions, Cerrado core and ecotonal populations showed higher

carotenoids:chlorophyll ratio when compared to Atlantic Forest, which may be

interpreted as a mechanism to maximize photoprotection (Demmig-Adams and Adams

1992). On the contrary, Atlantic Forest core and ecotonal populations showed

mechanisms to improve light interception, as higher chlorophyll concentration and

lower cholorophyll a:b ratio (Johnson et al. 1997, Dale and Causton 1992). As

discussed, differences among populations in leaf pigment are more likely to be

explained by local adaptation to light environment than to soil properties. These

differences in pigment composition among ecotypes, though, did not promote

differences in the evaluated photosynthesis traits.

Phenotypic plasticity

The results of this study suggest that soil properties are important in driving

morphological local adaptation of P. reticulata to either more competitive or more

stressful habitat, suggesting ecotypic differentiation between Atlantic Forest and

Cerrado populations, respectively. The ecotypic differentiation, however, was not

supported by pattern of variation in plasticity levels among populations. We expected to

find lower phenotypic plasticity in response to soil in Cerrado populations as it is

related to the stress resistance syndrome, being advantageous by preventing individuals

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from infertile habitat to grow too large under a temporally favorable circumstance that

may soon deteriorate (Chapin et al. 1993, Valladares et al. 2000a, b). On the other hand,

we expected to find higher plasticity in Atlantic Forest as higher competitors show

flexibility to respond rapidly to changes in the distribution of resource within the habitat

(Grime 2002). For P. reticulata, however, the evaluated traits showed a general pattern

of higher plasticity in populations from ecotonal area when compared to Atlantic Forest

and Cerrado core. Higher plasticity in ecotonal populations in response to soil could be

explained as a strategy of plants located in the boundary between biomes to adjust to

different soil environments, considering that plasticity is important in the process of

colonizing new ecological space (West-Eberhard 1989).

While comparing plastic responses to soil and to light (data reported in Chapter

2), we found that for chlorophyll and carotenoids:chlorophyll ratio plasticity in response

to light is significantly higher that in response to soil (T tests, respectively t=4.120,

p=0.0062 and t=2.460, p=0.0491). This result is in accordance to the fact that leaf

pigments content are more strongly influenced by light than soil. All the other evaluated

traits showed to be equally plastic in response to light and soil (p>0.05, data not shown),

showing that, for most of the traits, populations of P. reticulata are equally plastic in

response to these two different environmental factors. However, responses to light and

soil drive processes in different directions: responses to light show a major pattern of

higher plasticity in Atlantic Forest than in Cerrado populations, reinforcing ecotypic

differentiation (Chapter 2); this ecotypic difference was not corroborated by responses

to soil, for which higher plasticity was found in ecotonal populations.

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Survival in field conditions

The data showed that after 20 months in the field, individuals’ survival rate was

still dependent on the soil type used in the initial growth condition. The ones submitted

to Cerrado soil treatment during the nursery experiment showed higher mortality rate

than the ones submitted to Atlantic Forest soil treatment, independently of the

population provenance. This result is consistent with the fact that P. reticulata shows

association with nitrogen fixing microorganisms (Faria and Lima 1998) and during the

nursery experiment, seedlings submitted to forest soil probably had higher initial

mycorrhizal infection. In fact, a higher mycorrhizal infection in seedlings is known to

improve individuals’ success (Dickie et al. 2007).

No differences were observed in mortality rates among populations during the

studied period. It is early to conclude, though, that ecotypes do not differ in survival

during sapling phase and further censuses are needed. Plant success can be strongly

affected by extremes events and perturbations (Osmond et al. 1987) so the study period

may not have reflected yet the characteristic environmental conditions of the field sites.

Concluding remarks

The previous studies (Chapter 1 and 2) clearly suggested ecotypic differentiation

in P. reticulata populations in response to differences in light environment between

Atlantic Forest and Cerrado. The results of the present study also point to the existence

of ecotypes specialized to different soil conditions, although the evidences were not as

clear as for light. It is important to consider, though, that responses to soil are harder to

characterize than to light. Whereas light is characterized solely of a particular range of

photon flux densities and spectral distribution, soil properties are many and interact in a

complex manner (Dale and Causton 1992). Morphological differences found among

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populations were interpreted as adaptation to a more fertile and competitive habitat

(forest ecotype) or to a less fertile and stressful habitat (savanna ecotype). However, the

differences found among populations in leaf pigment are more likely to be explained by

local adaptation to light environment than to soil properties and forest and savanna

ecotypes could not be differentiated concerning phenotypic plasticity in response to soil

nor concerning survival in the field.

Hoffmann and Franco (2003) evaluated macroevolutionary responses across

savanna and forests by comparing congeneric pairs containing one Cerrado and one

Forest species and reported no difference in response to soil nutrient level between these

functional groups. The results of the present study add to this knowledge showing that

soil nutrient level may play a role in microevolution of Cerrado and Atlantic Forest

plants, although light environment is probably more important in driving the

evolutionary process.

References

Baltzer JL, Thomas SC. 2005. Leaf optical responses to light and soil nutrient availability in

temperate deciduous trees. American Journal of Botany 92(2): 214-223.

Baraloto C, Bonal D, Goldberg DE. 2006. Differential seedling growth response to soil resource

availability among nine neotropical tree species. Journal of Tropical Ecology 22: 487-497.

Chapin FS, Autumn K, Pugnaire F. 1993. Evolution of suites of traits in response to

environmental stress. American Naturalist 142: 78-92.

Dale MP, Causton DR. 1992. Use of the chlorophyll a/b ratio as a bioassay for the light

environment of a plant. Functional Ecology 6(2): 190-196.

Demmig-Adams B, Adams WW. 1992. Photoprotection and other responses of plants to high

light stress. Annual Review Plant Physiology and Plant Molecular Biology 43: 599-626.

Dickie IA, Montgomery RA, Reich PB, Schnitzer SA. 2007. Physiological and phenological

responses of oak seedlings to oak forest soil in the absence of trees. Tree Physiology 27:

133-140

Page 88: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

88

Dudley SA. 1996. The response to differing selection on plant physiological traits: evidence for

local adaptation. Evolution 50: 103-110.

Faria SM, Lima HC. 1998. Additional studies of the nodulation status of legume species in

Brazil. Plant and Soil 200: 185-192.

Field C. 1983. Allocating leaf nitrogen for the maximization on carbon gains: leaf age as a

control on the allocation program. Oecologia 56: 341-347.

Furley PA. 1992. Edaphic changes at the forest-savanna boundary with particular reference to

the neotropics. In: Nature and dynamics of forest-savanna boundaries (Furley PA, Proctor J,

Ratter JA, eds). Chapman & Hall: London.

González-Astorga J, Vovides AP, Iglesias C. 2003. Morphological and geographic variation of

the cycad Dioon edule Lindl. (Zamiaceae): ecological and evolutionary implications.

Botanical Journal of the Linnean Society 141: 465-470.

Goulart MF, Lemos Filho JP, Lovato MB. 2005. Phenological variation within and among

populations of Plathymenia reticulata in Brazilian Cerrado, Atlantic Forest and transitional

sites. Annals of Botany 96: 445-455.

Grime JP. 2002. Plant strategies, vegetation processes and ecosystem properties. John Wiley &

Sons: Chichester.

Haridasan M. 1992. Observations on soils, foliar nutrient concentrations and floristic

composition of cerrado sensu stricto and cerradão communities in central Brazil. In: Nature

and dynamics of forest-savanna boundaries (Furley PA, Proctor J, Ratter JA, eds). Chapman

& Hall: London.

Hoffmann WA, Moreira AG. 2002. The role of fire in population dynamics of woody plants.

In: The Cerrados of Brazil: ecology and natural history of a neotropical savanna. (Oliveira

PS, Marquis RJ). Columbia University Press: New York.

Hoffmann WA, Franco AC. 2003. Comparative growth analysis of tropical forest and savanna

woody plants using phylogenetically independent contrasts. Journal of Ecology 91: 475-

484.

Hoffmann WA, Orthen B, Franco AC. 2004. Constraints to seedling success of savanna and

forest trees across the savanna-forest boundary. Oecologia 140: 252-260.

Hoffmann WA, Franco AC, Moreira MZ, Haridasan M. 2005. Specific leaf area explains

differences in leaf traits between congeneric savanna and forest trees. Functional Ecology

19: 932-940.

Page 89: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

89

Hufford KM, Mazer SJ. 2003. Plant ecotypes: genetic differentiation in the age of ecological

restoration. Trends in Ecology and Evolution 18: 147-155.

Johnson JD, Tognetti R, Michelozzi M, Pinzauti S, Minotta G, Borghetti M. 1997.

Ecophysiological responses of Fagus sylvatica seedlings to changing light conditions. II.

The interaction of light environment and soil fertility on seedling physiology. Physiologia

Plantarum 101(1): 24-134.

Lacerda DR, Lemos Filho JP, Goulart MF, Ribeiro RA, Lovato MB. 2004. Seed dormancy

variation in natural populations of two tropical leguminous tree species: Senna multijuga

(Caesalpinoideae) and Plathymenia reticulata (Mimosoideae). Seed Science Research 14:

127-135.

Lawrence D. 2003. The response of tropical tree seedlings to nutrient supply: meta-analysis for

understanding a changing tropical landscape. Journal of Tropical Ecology 19: 239-250.

Lichtenthaler HK, Wellburn AR. 1983. Determination of total caroteoids and chlorophylls a and

b of leaf extract in different solvents. Biochemical Society Transactions. 11: 591-592.

Macel M, Lawson CS, Mortimer SR, Smilauerova M, Bischoff A, Crémieux LC, Dolezal J,

Edwards AR, Lanta V, Bezemer M, van der Putten WH, Igual JM, Rodriguez-Barrueco C,

Muller-Scharer H, Steinger T. 2007. Climate vs. soil factor in local adaptation of two

common plant species. Ecology 88(2): 424-33.

Nicotra BA, Chazdon RL, Schlichting CD. 1997. Patterns of genotypic variation and phenotypic

plasticity of light response in two tropical Piper (Piperaceae) species. American Journal of

Botany 84: 1542-1552.

Oliveira-Filho AT, Shepherd G J, Martins FR, Stubblenby WH. 1989. Environmental factors

affecting physiognomic and floristic variation in an area of cerrado in Central Brazil.

Journal of Tropical Ecology 5: 413-431.

Oliveira-Filho AT, Fontes MA. 2000. Patterns of floristic differentiation among Atlantic Forests

in Southeastern Brazil and the influence of climate. Biotropica 32: 793-810.

Oliveira-Filho AT, Ratter JA. 2002. Vegetation physiognomies and woody flora of the Cerrado

biome. In: The Cerrados of Brazil: ecology and natural history of a neotropical savanna

(Oliveira PS, Marquis RJ, eds). Columbia University Press: New York.

Osmond CB, Austin MP, Berry JA, Billings WD, Boyer JS, Dacey JWH, Nobel PS, Smith SD,

Winner WE. 1987. Stress physiology and the distribution of plants. BioScience 37(1): 38-

48.

Page 90: Diferenças adaptativas entre plantas de savanas e ...pos.icb.ufmg.br/pgecologia/teses/T51_Maira_F_Goulart.pdfo caso das populações de Plathymenia reticulata (Leguminosae-Mimosoideae)

90

Rascher U, Liebig M, Luttge U. 2000. Evaluation of instant light-response curves of chlorophyll

fluorescence parameters obtained with portable chlorophyll fluorometer on site in the filed.

Plant, Cell and Environment 23: 1397-1405.

Ratter JA, Ribeiro JF, Bridgewater S. 1997. The Brazilian Cerrado vegetation and threats to its

biodiversity. Annals of Botany 80: 223-230.

Reich PB, Walters MB, Ellswoth DS. 1992. Leaf life-span in relation to leaf, plant and stand

characteristics among diverse ecosystems. Ecological Monographs 62(3): 365-392.

Resende M, Lani JL, Rezende SB. 2002. Pedossistemas da Mata Atlântica: considerações

pertinentes sobre a sustentabilidade. Revista Árvore 26(3): 261-269.

Ruggiero PGC, Batalha MA, Pivello VR, Meirelles ST. 2002. Soil-vegetation relationships in

cerrado (Brazilian savanna) and semidecidous forest, Southeastern Brazil. Plant Ecology

160: 1-16.

Silvera K, Skillman JB, Dalling JW. 2003. Seed germination, seedling growth and habitat

partitioning in two morphotypes of the tropical pioneer tree Trema micrantha in a seasonal

forest in Panama. Journal of Tropical Ecology 19: 27-34.

Sultan SE, Bazzaz FA. 1993. Phenotypic plasticity in Polygonum persicaria. III. The evolution

of ecological breadth for nutrient environment. Evolution 47(4): 1050-1071.

Valladares F, Martinéz-Ferri E, Balaguer L, Peréz-Corona E, Manrique E. 2000a. Low leaf-

level response to light and nutrients in Mediterranean evergreen oaks: a conservative

resource-use strategy? New Phytologist 148: 79-91.

Valladares F, Wright JS, Lasso E, Kitajima K, Pearcy RW. 2000b. Plastic phenotypic response

to light of 16 congeneric shrubs from a Panamanian rainforest. Ecology 81(7): 1925-1936.

Valladares F, Sanchez-Gomez D, Zavala MA. 2006. Quantitative estimation of phenotypic

plasticity: bridging the gap between the evolutionary concept and its ecological

applications. Journal of Ecology 94: 1103-1116.

West-Eberhard MJ. 1989. Phenotypic plasticity and the origins of diversity. Annual Review of

Ecology and Systematic 20: 249-278.

Wijesinghe DK, John EA, Hutchings MJ. 2005. Does pattern of soil resource heterogeneity

determine plant community structure? An experimental investigation. Journal of Ecology

93: 99-112.