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

Abstract

A reduction in rainfall is predicted by climate models for some parts of the Amazon, and a decline in stomatal conductance (gs) is often the main effect of drought. The physiological effect of soil water deficit on other physiological traits has been little investigated in Amazonian trees. In this work we assess the effect of soil water deficit on leaf pigment content, gas exchange, chlorophyll fluorescence, total leaf area (AL), 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 soil water deficit for 90 days, when several physiological parameters were measured. Water deficit 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 − 0.72 MPa (SWC at 25% FC) to − 0.29 MPa in well-irrigated plants. Subjecting the plants to soil water 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 plants did not reduce stomatal conductance (gs) 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 AL substantially declined, at a SWC of 25% FC. Drastic reduction of AL in plants exposed to SWC of 25% FC contributed to a reduction in total biomass accumulation, and a drop in AL resulted in a decline in CUW in this treatment. These results show that although there is no effect of moderated water stress on photosynthesis, gs or photochemical responses, there is a remarkable effect of moderate drought on biomass accumulation. © 2018, Brazilian Society of Plant Physiology.