Variações e impactos da capacitância na floresta amazônica

Abstract

Stored water, defined as the amount of water available in a tissue or the entire plant, provides significant contributions to transpiration and hence directly influences whole-tree gas exchange. Whole-plant water storage is a function of reservoir size (e.g. sapwood volume) and of capacitance, or the amount of water released per unit change in water potential. Although water storage plays a critical role in buffering plant water fluxes, there is little information regarding its role in supporting transpiration in the Amazon rainforest. We investigated the influence of stored water and capacitance at wood, leaf, and tree levels on gas exchange within a mature forest in the central Amazon. Trees with larger sapwood area had more stored water and greater total daily transpiration. Wood capacitance and storage capacity were closely associated with wood density, a variable related in other studies to the vital rates of tree species, suggesting potential implications for the life history these individuals. Leaf capacitance was coordinated with the hydraulic conductivity, favoring species with high capacitance and hydraulic conductivity to maintain higher water potentials and higher gas exchange rates. Great time lag between base and top sap flow corresponded to a long duration at which max sap flow could be maintained. We conclude that capacitance significantly influences gas exchange and shapes the life history of trees in the Central Amazon. We characterize it as a hydraulic strategy employed to avoid drought effects, using water reserves to buffer water stress. This strategy positively contributes to carbon and water economy of these forests.