Leaf hydraulic conductance and the vulnerability to water deficits have profound effects on plant distribution and mortality. In this study, we compiled a leaf hydraulic trait dataset with 311 species-at-site combinations from biomes worldwide. These traits included maximum leaf hydraulic conductance ( K leaf ), water potential at 50% loss of K leaf (P50 leaf ), and minimum leaf water potential ( Ψ min ). Leaf hydraulic safety margin (HSM leaf ) was calculated as the difference between Ψ min and P50 leaf . Our results indicated that 70% of the studied species had a narrow HSM leaf (less than 1 MPa), which was consistent with the global pattern of stem hydraulic safety margin. There was a positive relationship between HSM leaf and aridity index (the ratio of mean annual precipitation to potential evapotranspiration), as species from humid sites tended to have larger HSM leaf . We found a significant relationship between K leaf and P50 leaf across global angiosperm woody species and within each of the different plant groups. This global analysis of leaf hydraulic traits improves our understanding of plant hydraulic response to environmental change.

Background and Aims Leaf biomechanical resistance protects leaves from biotic and abiotic damage. Previous studies have revealed that enhancing leaf biomechanical resistance is costly for plant species and leads to an increase in leaf drought tolerance. We thus predicted that there is a functional correlation between leaf hydraulic safety and biomechanical characteristics. Methods We measured leaf morphological and anatomical traits, pressure–volume parameters, maximum leaf hydraulic conductance (Kleaf-max), leaf water potential at 50% loss of hydraulic conductance (P50leaf), leaf hydraulic safety margin (SMleaf), and leaf force to tear (Ft) and punch (Fp) of 30 co-occurring woody species in a subtropical evergreen broadleaved forest. Linear regression analysis was performed to examine the relationships between biomechanical resistance and other leaf hydraulic traits. Key Results We found that higher Ft and Fp values were significantly associated with a lower (more negative) P50leaf and a larger SMleaf, thereby confirming the correlation between leaf biomechanical resistance and hydraulic safety. However, leaf biomechanical resistance showed no correlation with Kleaf-max, although it was significantly and negatively correlated with leaf outside-xylem hydraulic conductance. In addition, we also found that there was a significant correlation between biomechanical resistance and the modulus of elasticity by excluding an outlier. Conclusions The findings of this study reveal leaf biomechanical-hydraulic safety correlation in subtropical woody species.

Aims Vessel, fibers, and parenchyma are the main components of tree xylem. They are responsible for water transport, mechanical support, and water and nutrients storage. Given the limited xylem space, consistent investment in one type of tissue would constrain the space available for other types of tissue, thus resulting in a possible trade-off among different tissues in their fractions. Analysis of the fractions of tissue types in xylem and the trade-off would contribute to better understanding of the eco-physiological adaptation of plants. Methods We selected 21 characteristic tree species (10 deciduous and 11 evergreen) from a mixed evergreen and deciduous broad-leaved forest located in the mid-subtropical karst region, and measured their xylem tissue fractions. In addition, we calculated the hydraulic-related structural traits in xylems and examined the correlations among various traits. Important findings Compared to the global average values of xylem tissue fractions, the karst tree species tended to have a higher proportion of parenchyma. The fraction of vessel lumen was not correlated with fiber and parenchyma fractions across the tree species investigated. Instead, a significant trade-off was observed between fractions of fiber and parenchyma. A trade-off between the hydraulic efficiency (i.e. theoretical hydraulic conductivity) and safety (vessel wall reinforcement) was observed across both the deciduous and the evergreen tree species. The two contrasting group of karst trees differenced significantly in the intercepts of the lines for trade-offs.

Water availability in karst forests is temporally and spatially heterogeneous; thus, xylem hydraulic efficiency, safety and water storage are potential drivers of tree growth. We selected 21 tree species from a primary subtropical karst forest in southern China and analyzed the contribution of xylem hydraulic efficiency, safety, and water storage to the growth of karst trees. The results showed that large vessel diameter, strong connectivity between vessels and axial parenchyma, and high saturated water content (SWC) led to high xylem hydraulic conductivity (Ks). SWC traded off against embolism resistance (P50). Ks had the strongest relationship with the average diametral growth rate (DGR). In large trees, both high Ks and more negative P50 were associated with high DGR. Through a growth-size relationship model, DGR acceleration was positively correlated with embolism-resistance across species. This study shows that xylem hydraulic efficiency and safety influenced growth rate and growth dynamics in karst tree species.

The evolution of xylem vessels and dense leaf vein networks in flowering plants enabled unprecedented increases in plant water transport and rates of CO2 assimilation. We tested the hypothesis that independent of vein density, higher leaf vein topological efficiency (VTE), achieved with denser free vein endings, would reduce the extraxylary pathlength, further benefitting whole-leaf conductance, while reducing carbon investment, and releasing space for light capture. Our analysis across 52 phylogenetically diverse angiosperm species demonstrated that for a given vein density, high VTE conferred by dense free endings can shorten the extraxylary pathlength by up to 11%. Across species, high VTE was associated with high stomatal conductance, non-vein area fraction for light capture, and low leaf mass per area. Our findings identify leaf vein topological efficiency as an important measure of the use of leaf space and biomass, and a key factor influencing plant adaptation to historical and future environmental conditions.