Leaf hydraulic capacity and drought vulnerability: possible trade-offs and correlations with climate across three major biomes

1. Leaf hydraulic capacity and vulnerability to drought stress are key determinants of plant competitive ability and productivity. Yet, it is not clear how these traits correlate to climatic variables across biomes and whether a trade-off exists between them. 2. We collected leaf hydraulics data for 130 woody angiosperms from selected published articles. Species-specific values of leaf hydraulic capacity on a leaf area (K-leaf_area) and dry mass (K-leaf_mass) basis, leaf water potential inducing 50% loss of K-leaf (P-50), as well as climatic variables (mean annual temperature, MAT and precipitation, MAP) for study sites were collected. Species were classified as belonging to three major biomes, that is dry sclerophyllous forests (DSF), temperate forests (TMF) and tropical forests (TRF). 3. Significant differences were observed between biomes, with DSF species displaying the lowest hydraulic efficiency (low K-leaf) and the highest resistance to drought stress (low P-50). P-50 was correlated with both MAP and MAT, with species from low precipitation habitats having the lowest P-50 values. Both K-leaf_area and K-leaf_mass were positively correlated with MAP and MAT. Leaf gas exchange rates were positively correlated with both K-leaf_area and K-leaf_mass. Although no correlation was found between P-50 and K-leaf_area, a weak trade-off between leaf hydraulic safety and capacity emerged when P-50 was plotted versus K-leaf_mass. 4. Leaf hydraulics emerge as an important functional trait underlying plant adaptation to different habitats and contributing to shape vegetation features in different biomes.