Leaf vein topology confers water transport efficiency

The evolution of xylem vessels and dense leaf venation in angiosperms enabled unprecedented increases in water transport and CO2 assimilation rates. We tested the hypothesis that independent of vein density, high leaf vein topological efficiency (VTE), reduces the extraxylary pathlength, benefitting whole-leaf conductance, reducing carbon investment and releasing space for light capture. We developed a novel approach quantifying the effect of vein topology on extraxylary pathlength, measured minor vein and stomata structure, and constructed leaf pressure-volume curves across 52 phylogenetically diverse angiosperms. For a given vein density, high VTE conferred by dense free-ending veinlets shortened the extraxylary pathlength by up to 11%. High VTE correlated with high stomatal conductance, non-vein area fraction for light capture, and low leaf mass per area. Our findings identify VTE 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.