Linking leaf hydraulic properties, photosynthetic rates, and leaf lifespan in xerophytic species: a test of global hypotheses.

Abstract

Leaf venation and its hierarchal traits are crucial to the hydraulic and mechanical properties of leaves, reflecting plant life-history strategies. However, there is an extremely limited understanding of how variation in leaf hydraulics affects the leaf economic spectrum (LES) or whether venation correlates more strongly with hydraulic conductance or biomechanical support among hierarchal orders. We examined correlations of leaf hydraulics, indicated by vein density, conduit diameter, and stomatal density with light-saturated photosynthetic rates, leaf lifespan (LLS), and leaf morpho-anatomical traits of 39 xerophytic species grown in a common garden. We found positive relationships between light-saturated, area-based photosynthetic rates, and vein densities, regardless of vein orders. Densities of leaf veins had positive correlations with stomatal density. We also found positive relationships between LLS and vein densities. Leaf area was negatively correlated with the density of major veins but not with minor veins. Most anatomical traits were not related to vein densities. We developed a network diagram of the correlations among leaf hydraulics and leaf economics, which suggests functional trade-offs between hydraulic costs and lifetime carbon gain. Leaf hydraulics efficiency and carbon assimilation were coupled across species. Vein construction costs directly coordinated with the LLS. Our findings indicate that hierarchal orders of leaf veins did not differ in the strength of their correlations between hydraulic conductance and biomechanical support. These findings clarify how leaf hydraulics contributes to the LES and provide new insight into life-history strategies of these xerophytic species.