ABSTRACT Water deficit is most frequent in forest physiognomies subjected to climate change. As a consequence, several tree species alter tissue water potential, gas exchange and production of carbon compounds to overcome damage caused by water deficiency. The working hypothesis, that a reduction in gas exchange by plants experiencing water deficit will affect the composition of carbon compounds in soluble sugars, lipids and vegetative structures, was tested on Copaifera langsdorffii. Stomatal conductance, leaf water potential, and CO2 assimilation rate declined after a period of water deficit. After rehydration, leaf water potential and leaf gas exchange did not recover completely. Water deficit resulted in 13C enrichment in leaves, soluble sugars and root lipids. Furthermore, the amount of soluble sugars and root lipids decreased after water deficit. In rehydration, the carbon isotopic composition and amount of root lipids returned to levels similar to the control. Under water deficit, 13C-enriched in root lipids assists in the adjustment of cellular membrane turgidity and avoids damage to the process of water absorption by roots. These physiological adjustments permit a better understanding of the responses of Copaifera langsdorffi to water deficit.

RESUMO A intensidade e a frequência dos períodos de seca aumentaram de acordo com as predições de mudanças climáticas. A superação e rápida recuperação são características adaptativas importantes para espécies de plantas encontradas em regiões que apresentam períodos de falta d’água. Copaifera langsdorffii é uma espécie neotropical que desenvolveu folhas com adaptações morfológicas e mecanismos fisiológicos que permitem a sobrevivência em ambientes com estresse hídrico sazonal. O objetivo deste trabalho foi observar as respostas fisiológicas substanciais para a economia de água e possíveis danos representativos à reação fotoquímica depois de expor as plantas ao estresse hídrico e posterior reidratação. Mesmo após a reidratação, as plantas apresentaram mecanismos para controlar a perda de água através da menor condutância estomática. A rápida reidratação das folhas foi indicada pelos valores de conteúdo relativo de água semelhante às folhas não estressadas. A condutância estomática foi à única variável que apresentou alto índice de plasticidade. Na atividade fotoquímica, a espécie apresentou maior dissipação fotoquímica, taxa de transporte de elétrons e rendimento quântico efetivo do fotossistema II, quando submetidas à reidratação após o período de estresse hídrico. Os resultados sugerem que C. langsdorffii apresentou rápida reidratação e maior eficiência fotoquímica mesmo após restrição hídrica. Mostrando que esta espécie pode ser utilizada como modelo em estudos fisiológicos devido ao seu ajuste desenvolvido em resposta a diferentes regimes ambientais.

ABSTRACT The intensity and frequency of drought periods has increased according to climate change predictions. The fast overcome and recovery are important adaptive features for plant species found in regions presenting water shortage periods. Copaifera langsdorffii is a neotropical species that has developed leaves presenting physiological mechanisms and morphological adaptations that allow its survival under seasonal water stress. We aimed in this work to observe substantial physiological responses for water saving and damage representative to the photochemical reaction after exposed plants to water stress and to subsequent recovery. We found in plants mechanisms to control water loss through the lower stomatal conductance, even after rehydration. It goes against the rapid recovery of leaves, indicated by the relative water content values restored to previously unstressed plants. Stomatal conductance was the only variable presenting high plasticity index. In photochemical activity, the species presented higher photochemical quenching, electron transport rate and effective quantum yield of photosystem II when they were subjected to rehydration after water stress period. Our results suggest that C. langsdorffii presented rapid rehydration and higher photochemical efficiency even after water restriction. These data demonstrate that this species can be used as a model for physiological studies due to the adjustment developed in response to different environmental schemes.