# sPlot Project \#31 - The adaptive value of xylem physiology within and across global ecoregions
*Lead authors*
Daniel C. Laughlin, & Jesse Robert Fleri - Department of Botany, University of Wyoming, Laramie, WY 82071 USA
*Project outline:*
Environmental filtering is a key process in community assembly that sorts species along environmental gradients according to variation in ecophysiological tolerance. However, our current understanding of how traits explain turnover in community composition along environmental gradients at a global scale is limited to easy-to-measure morphological traits. Plant establishment and survival requires the capacity to conduct water through its tissues when water is available and the ability to resist drought-induced embolism when water is scarce. Databases of xylem vulnerability (P50) and hydraulic conductance (Ks) have recently been published including approximately 1000 common woody species.
We propose to determine how xylem physiology influences the likelihood that a species can occur in a particular environment by integrating a database of xylem physiological traits with the sPlot database of vegetation plots. Climate and soil variables for each plot will be extracted from other available databases. This unprecedented integration of the two largest databases of their kind would facilitate the most powerful statistical analysis to test how xylem traits vary along climate and soil gradients globally.
We will test the adaptive value of xylem traits by fitting a hierarchical mixed effects model to determine whether species occurrence is a function of interactions between xylem traits and environmental gradients within and across global ecoregions. In other words, we will test whether species occurrence in a given environment depends on their xylem properties. This global scale analysis will substantively advance our understanding of how xylem traits vary along global environmental gradients.
