Leaf vein density enhances vascular redundancy instead of carbon uptake at the expense of increasing water leaks in oaks

Abstract

Predicting plant growth from functional traits has been a long-term goal of experimental botany. Early studies considered that resource traits align across a single axis, from high to low growth rates. The drivers of nocturnal and cuticular leaf conductances have received much recent attention, but how they align with other functional traits along axes of resource use remains to be investigated. Here we examined correlated evolution of secondary growth, leaf economic, stomatal, venation and gas exchange traits across 12 Quercus species growing in a common garden. Variation in growth correlated with variation in assimilation and nocturnal conductance (gn). Our observations are consistent with the hypothesis of a negative relationship between SLA and leaf vein density (VLAall) within oaks, indicating that increased VLAall is a strategy to enhance leaf vascular redundancy against stress or perturbation as the degree of sclerophylly increases. gn was negatively correlated with growth and decoupled from daytime conductance and photosynthesis. gn seemed to be a passive process in this genus, apparently driven by enhanced water supply that results from increased VLAall. We also observed a positive relationship between leaf vein density and cuticular conductance, indicating that increasing VLAall may incur significant water costs under strong drought.