Is a reduction in stomatal conductance the main strategy of Garcinia brasiliensis (Clusiaceae) to deal with water stress?

摘要

A reduction in rainfall is predicted by climate models for some parts of the Amazon, and a decline in stomatal conductance (g(s)) is often the main effect of drought. The physiological effect of soilwaterdeficit on other physiological traits has been little investigated in Amazonian trees. In this work we assess the effect of soilwaterdeficit on leaf pigment content, gasexchange, chlorophyll fluorescence, total leaf area (A(L)), consumptive use of water (CUW, total amount of water used for irrigation), and biomass accumulation. Plants of Garcinia brasiliensis were grown in pots under greenhouse conditions and submitted to soilwater deficit for 90days, when several physiological parameters were measured. Waterdeficit was induced by reducing soil water content (SWC) to 25, 50 and 75% of field capacity (FC). The control was soil at 100% FC. Midday leaf water potential varied from -0.72MPa (SWC at 25% FC) to -0.29MPa in well-irrigated plants. Subjecting the plants to soilwater deficit did not affect light saturating photosynthesis, leaf pigment content, Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco) activity or fluorescence parameters. Under moderate water stress Garcinia plantsdid not reduce stomatal conductance (g(s)) which remained rather unchanged. Instead, we found that mild water stress led to an increase in total non-structural carbohydrates, and as the stress progressed A(L) substantially declined, at a SWC of 25% FC. Drastic reduction of A(L) in plants exposed to SWC of 25% FCcontributed to a reduction in total biomass accumulation, and a drop in A(L) resulted ina decline in CUWin this treatment. These results show that although there is no effect of moderated water stress on photosynthesis, g(s) or photochemical responses, there is a remarkable effect of moderate drought on biomass accumulation.