Leaf vein topology confers water transport efficiency

Abstract The evolution of xylem vessels and dense leaf vein networks in flowering plants enabled unprecedented increases in plant water transport and rates of CO2 assimilation. We tested the hypothesis that independent of vein density, higher leaf vein topological efficiency (VTE), achieved with denser free vein endings, would reduce the extraxylary pathlength, further benefitting whole-leaf conductance, while reducing carbon investment, and releasing space for light capture. Our analysis across 52 phylogenetically diverse angiosperm species demonstrated that for a given vein density, high VTE conferred by dense free endings can shorten the extraxylary pathlength by up to 11%. Across species, high VTE was associated with high stomatal conductance, non-vein area fraction for light capture, and low leaf mass per area. Our findings identify leaf vein topological efficiency as an important measure of the use of leaf space and biomass, and a key factor influencing plant adaptation to historical and future environmental conditions.