Résumé
Introduction: The anatomical composition of wood underpins hydraulic transport and storage functions of trees. Together, anatomical traits of the vessels, fibers, and parenchyma influence the plants resistance to embolism formation (P50) and availability of internal water storage (sapwood capacitance), both of which can impact hydraulic vulnerability under drought stress. However, the degree to which interspecific variation in anatomical traits correspond with measures of hydraulic vulnerability has not been extensively studied in tropical angiosperms.Objectives: We compared a suite of xylem anatomical measurements to measures of embolism resistance and stem sapwood capacitance for branches from five individuals of twelve species representing a range of life history strategies in a tropical rainforest in Puerto Rico.We asked: (1) how do stem anatomical traits correlate with embolism resistance and sapwood capacitance? (2) how do structure-function relationships vary across species with different life-history traits? Methods: We used a sledge microtome and high-resolution slide scanner with digital analysis software to quantify a suite of anatomical traits (vessel dimensions, potential hydraulic conductivity, vessel grouping indices) of branch-wood cross sections, and compared these with hydraulic traits (P50 and stem capacitance) previously collected on the same individuals.Results: We found correlations at the site level between hydraulic traits (P50 and sapwood capacitance), and anatomical traits (including the size and grouping of vessels). Vessel diameter and vessel density were negatively and positively correlated, respectively, with more embolism resistant P50 values. While vessel diameter and the vessel grouping index were positively correlated with sapwood capacitance and vessel density was negatively correlated.Conclusions: At the site level, vessel characteristics were related to hydraulic traits indicating a link in how branches manage hydraulic stress. These results suggest that the anatomical design of a tree's xylem has implications on its ability to manage different kinds of drought stress; therefore, a better understanding of anatomical traits and their inter- and intraspecific variability will help to improve our understanding of trees' hydraulic vulnerability.