Trade-offs between leaf hydraulic capacity and drought vulnerability: morpho-anatomical bases, carbon costs and ecological consequences

Leaf hydraulic conductance (Kleaf) and vulnerability constrain plant productivity, but no clear trade-off between these fundamental functional traits has emerged in previous studies. We measured Kleaf on a leaf area (Kleaf_area) and mass basis (Kleaf_mass) in six woody angiosperms, and compared these values with their distribution and leaf tolerance to dehydration in terms of P50 i.e. the leaf water potential inducing 50% loss of Kleaf. We also measured several morphological and anatomical traits associated with carbon investment into leaf construction and water transport efficiency. Clear relationships emerged between Kleaf_mass, P50, and LMA, suggesting that increased tolerance to hydraulic dysfunction implies increased carbon costs for water use. Low P50 values were associated with narrower and denser vein conduits, increased thickness of conduit walls, and increased vein density. This, in turn, was associated with reduced leaf surface area. Leaf P50 was closely associated with the plants’ distribution over a narrow geographical range, suggesting that this parameter contribute to shape vegetation features. Our data also highlight the carbon costs associated with increased leaf tolerance to hydraulic dysfunction, which confers to some species the ability to thrive under reduced water availability but likely decrease their competitiveness in high-resource habitats.