Canopy water status and photosynthesis of tropical trees are associated with trunk sapwood hydraulic properties

Tree trunks not only provide physical support for canopy leaves but also supply and store water for transpiration. However, the relationships between trunk hydraulic properties and canopy leaf physiology in tropical trees are not well-understood. In this study we concurrently measured morning and midday canopy leaf photosynthesis (A), stomatal conductance (g(s)), and leaf water potentials (psi(L)) in 40 tropical trees representing 14 species at the beginning of the rainy season in Xishuangbanna, Southwest China. We also measured trunk sapwood capacitance (C), wood density, and sap flux density to assess their association with canopy leaf physiology. Among the 14 studied species, only three and four species did not show a significant midday reduction in A and g(s) respectively. The diurnally maximum A and g(s) were significantly positively related to sapwood hydraulic capacitance, maximum sap flux density (midday), and sap flux density at 11:00. Those species with lower wood density and higher C showed a lower reduction in psi(L) at midday, whereas, species with high C, and large values of maximum sap flux density also showed high carbon assimilation at midday. Our results provide new insights into the close coordination between canopy physiology and trunk sapwood hydraulic properties in tropical trees.