Hydraulic efficiency of the leaf venation system in sun- and shade-adapted species

We tested the hypothesis that leaf hydraulics is correlated with the light adaptation of different plant species and specifically that the hydraulic resistance of the leaf venation (R_venation) is lower in sun- than in shade-adapted species. R_venation was measured in six sun- and six shade-adapted species with a high-pressure flow meter (HPFM). The number of conduits at the proximal third of the midrib was counted and the diameter of the widest conduits together with vein density were measured. R_venation was higher in shade species than in sun species and it was negatively correlated with the mean diameter of the widest conduits. Maximum leaf conductance to water vapour recorded for the different species was negatively correlated with the corresponding R_venation. Sun-adapted species coping with the high water demand typical of sunny habitats appeared to have developed a highly efficient conducting system to supply living mesophyll cells with water. In contrast, species adapted to shady habitats showed higher R_venation values according to their lower need for investment of carbon into producing wide conduits in the leaf.