Leaf venation is a key trait determining leaf water relations and mechanical stability. Since contribution of leaf vein to mechanical properties, however, has not been understood well, our understanding of how leaf vein architecture adjusts these two functions within leaf is limited. Here, we tested hypothesis that leaf water use and mechanical properties would be more correlating with lower- and higher- order vein density (VLA), respectively.

We studied eight Fagaceae species, growing in temperate forests and differing in leaf and vein morphological characteristics. We quantified two leaf water use traits, two mechanical properties and nine traits relating both vein architecture and leaf structure.

Across species, primary and secondary vein density (VLA1.2) correlated positively to lamina strength and leaf structural traits but not to water use. In contrast, minor vein density (VLAmin) correlated to lamina hydraulics positively but not to mechanical properties and leaf structural traits.

Our results indicate (1) VLA1.2 influences leaf structural and mechanical properties, (2) VLAmin affect leaf water use thus, potentially gas exchange capacity. These findings suggest vein hierarchy is associated with functional differentiation among vein orders in supporting leaf functions.