Fig. 5

Water potential threshold inducing 50% loss of conductivity (P₅₀) of stem (P_50stem) plotted against that of leaf (P_50leaf) showing the commonality of vulnerability segmentation across tree species. Data were compiled from published literature in which P₅₀ of different organs were measured on the same set of plants, including the 63 species reported in Zhu et al. (2016). Blue circles indicate P_50leaf that was estimated by assessing the dynamics of whole leaves, which incorporate the extra-xylary pathway. Alternatively, P_50leaf can be measured from midrib (red circle)/petiole (red square), or exclusively from the xylem network of leaves (e.g. microCT or optical technique), in which only the conductivity of xylem tissues is accounted for (red diamond). The solid line represents the 1:1 relationship. Inset boxplot shows the distribution of hydraulic safety margin (HSM, MPa; defined as P_50stem-P_50leaf)