LB 23-202 - Regulation of whole-tree hydraulic conductance in tropical forests across a steep climatic gradient

Plant transpiration regulates the global energy balance between earth and atmosphere. Tropical forests play a substantial role in recycling water through evapotranspiration. It is therefore crucial to understand the drivers of the magnitude of tropical forest transpiration and associated physiological mechanisms in different spatial and temporal scales. We monitored sap flow rate, calculated whole tree crown conductance, and measured leaf gas exchange, leaf temperature, and hydraulic parameters of 28 tree species in three tropical forests sites in Panama along a steep precipitation gradient. The main objective was to investigate whether crown conductance and stomatal conductance were coordinated across the climate transect and in relation to life history strategy and associated traits. Leaf and air temperature were typically decoupled across the sites and was corrected for in estimates of crown conductance. Our results showed that crown conductance significantly varied between species, sites, and different functional groups. Significantly higher crown conductance was observed in dry forest site than in the wet forest. Crown conductance was strongly correlated with vapor pressure deficit (VPD) corrected for the decoupling of air and leaf temperature. Evergreen and shade tolerant species had higher stomatal conductance than the deciduous and light demanding species. In all three sites, crown conductance was found to be coordinated with leaf stomatal conductance, wood density, specific leaf area and leaf and stem hydraulic traits. We conclude that species functional traits and environmental heterogeneity should be taken into account in predicting canopy transpiration of tropical forests.