The links between leaf hydraulic vulnerability to drought and key aspects of leaf venation and xylem anatomy among 26 Australian woody angiosperms from contrasting climates

• Background and Aims The structural properties of leaf venation and xylem anatomy strongly influence leaf hydraulics, including the ability of leaves to maintain hydraulic function during drought. Here we examined the strength of the links between different leaf venation traits and leaf hydraulic vulnerability to drought (expressed as P50 _leaf by rehydration kinetics) in a diverse group of 26 woody angiosperm species, representing a wide range of leaf vulnerabilities, from four low-nutrient sites with contrasting rainfall across eastern Australia. 

• Methods For each species we measured key aspects of leaf venation design, xylem anatomy and leaf morphology. We also assessed for the first time the scaling relationships between hydraulically weighted vessel wall thickness (t _h ) and lumen breadth (b _h ) across vein orders and habitats. 

• Key Results Across species, variation in P50 _leaf was strongly correlated with the ratio of vessel wall thickness (t _h ) to lumen breadth (b _h ) [(t/b) _h ; an index of conduit reinforcement] at each leaf vein order. Concomitantly, the scaling relationship between t _h and b _h was similar across vein orders, with a log–log slope less than 1 indicating greater xylem reinforcement in smaller vessels. In contrast, P50 _leaf was not related to t _h and b _h individually, to major vein density (Dv _major ) or to leaf size. Principal components analysis revealed two largely orthogonal trait groupings linked to variation in leaf size and drought tolerance.

• Conclusions Our results indicate that xylem conduit reinforcement occurs throughout leaf venation, and remains closely linked to leaf drought tolerance irrespective of leaf size.