Effect of atmospheric CO2 enrichment on the establishment of seedlings of Jatobá, Hymenaea Courbaril L. (Leguminosae, Caesalpinioideae)

ARTICLES

Effect of atmospheric CO₂ enrichment on the establishment of seedlings of Jatobá, Hymenaea Courbaril L. (Leguminosae, Caesalpinioideae)

Aidar, M.P.M.^I; Martinez, C.A.^II; Costa, A.C.^III; Costa, P.M.F.^I; Dietrich, S.M.C.^I; Buckeridge, M.S.I, ^*

^ISeção de Fisiologia e Bioquímica de Plantas, Instituto de Botânica, CP4005 CEP 01061-970, São Paul

^IIDepartamento de Biologia, FFCLRP, USP, 14040-901, Ribeirão Preto, São Paulo

^IIIDepartamento de Biologia Vegetal, UFV, 36571-000, Viçosa, Minas Gerais

ABSTRACT

Plants grown in elevated CO₂ environments may exhibit photosynthetic acclimation or down regulation, which is characterised by reduced rates of photosynthesis. In most cases of CO₂-induced photosynthetic acclimation, the reduced rates of photosynthesis were still higher than those detected in plants growing at ambient CO₂ concentrations. In this work we present a study on the behaviour of seedlings of Hymenaea courbaril, a late secondary/climax species that is one of the most important trees in mature tropical forests of the Americas. After germination, the seedling of H. courbaril increases its rate of growth due to the mobilisation of massive amounts of a storage cell wall polysaccharide (xyloglucan) from its cotyledons. In our experiments, germinated seeds were incubated in open top chambers with increased concentration of atmospheric CO₂ (720 ppm) (control at 360 ppm). To test the effects of the presence of the storage compound on the responses of growing seedlings, cotyledons were detached before the start of polysaccharide mobilisation and parameters such as dry mass, leaf area, CO₂ assimilation rates and chlorophyll a fluorescence were measured during 98 days. A comparison between 360 and 720ppm growing seedlings showed a significant increase in leaf area only in metaphylls of seedlings growing under higher CO₂. However, a marked and persistent increase (2 fold) in photosynthesis (CO₂ assimilation) was observed in all cases (with or without cotyledons). Changes in the levels of sucrose have been suggested to act as a signalling mechanism that switches on/off the storage or development mode in plant tissues. Thus, the explanation for our general observation that the differential response in terms of growth of seedlings ceases to exist when storage mobilisation is functioning, might be related to the fact that higher levels of sucrose are produced as a result of carbon storage compounds degradation. By the results obtained, it appears that plants grown under enriched CO₂ did not acclimate and therefore under the climatic conditions forecasted on the basis of the present carbon dioxide emissions, Hymenaea courbaril should establish faster in its natural environment and might also serve as an efficient mechanism of carbon sequestration within the forest.

Key Words: Photosynthesis; CO₂ enrichment; Hymenaea courbaril; storage mobilisation; root:shoot ratio; seedling growth; cotyledons; open top chamber; xyloglucan; biodiversity

RESUMO

Plântulas de jatobá crescidas em ambiente com concentrações elevadas de CO₂ podem exibir aclimatação fotossintética ou retro-inibição, a qual é caracterizada pela redução das taxas fotossintéticas. Em muitos casos de aclimatação induzida por alto CO₂, taxas reduzidas de fotossíntese são observadas, mas ainda são mais altas que aquelas detectadas em plantas crescendo em concentrações atuais de CO₂ atmosférico (360ppm). No presente trabalho, realizamos um estudo do comportamento de plântulas de Hymenaea courbaril, uma espécie secundária tardia/clímax de grande importância em florestas tropicais maduras nas Américas. Em nossos experimentos, sementes recém germinadas foram cultivadas em câmaras de topo aberto com concentrações alteradas de CO₂ (720 ppm e controle a 340 ppm). Para testar os efeitos da presença de compostos de reserva sobre as respostas de plântulas em crescimento, cotilédones foram destacados antes do início da mobilização do polissacarídeo de reserva (xiloglucano) e parâmetros tais como massa seca, área foliar, assimilação de CO₂ e fluorescência da clorofila a, foram medidos durante 98 dias. A comparação entre plântulas crescendo em atmosfera de CO₂ a 360 e 720 ppm, mostraram aumento siginificativo em área foliar apenas nos metáfilos de plântulas crescendo nas concentrações mais altas. No entanto, um efeito marcado e consistente de aumento na fotossíntese (assimilação de CO₂) foi observado em todos os casos (com e sem cotilédones). Acredita-se que as variações nos níveis de sacarose podem funcionar como um mecanismo sinalizador de alterações nos estados de armazenamento ou desenvolvimento de tecidos vegetais. Portanto, uma possível explicação para nossas observações gerais de que uma resposta diferencial em termos de crescimento de plântulas deixa de existir quando a mobilização de reservas está em curso, pode estar relacionada com o fato de que altos níveis de sacarose são produzidos quando há degradação de compostos de reservas. De acordo com nossos resultados, parece que as plantas crescidas sob concentrações enriquecidas de CO₂ não aclimataram e portanto, sob as condições climáticas previstas com base nos níveis atmosféricos atuais, plântulas de Hymenaea courbaril deverão estabelecer mais rapidamente em seu ambiente natural e podem também servir como um mecanismo eficiente de seqüestro de carbono pela floresta.schottiana Mart.. Phytoseiidae foi a segunda família mais numerosa (11,2% dos ácaros coletados), sendo a mais abundante em folíolos.

Palavras-chave: Fotossíntese; enriquecimento CO₂ atmosférico; Hymenaea courbaril; mobilização de reservas; razão raíz:parte aérea; crescimento e estabelecimento de plântula; cotilédones; câmara de topo aberto; xiloglucano; biodiverisdade

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ACKNOWLEDGEMENTS

This work was supported by BIOTA-FAPESP (grant number 98/05124-8). MSB and SMCD acknowledge a research productivity fellowship by CNPq. PFC acknowledges a MSc fellowship by CNPq. Authors acknowledge the Federal University of Viçosa for the use of the CO₂ research facilities.

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Date received: June,08, 2002 - Accepted: June, 30, 2002

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Publication Dates

• Publication in this collection
  11 June 2013
• Date of issue
  2002

History

• Accepted
  30 June 2002
• Received
  08 June 2002