Vulnerability segmentation is vital to hydraulic strategy of tropical–subtropical woody plants

Abstract The vulnerability segmentation hypothesis proposes that the hydraulic function of expensive stems can be protected by sacrificing cheap leaves, which has been proven to be a key strategy to survive drought for woody species from arid regions. Climate change has caused increasing severe droughts in relatively humid tropical‐subtropical forests. However, whether vulnerability segmentation (measured as the differences in embolism resistance between stem and leaf; P 50 leaf–stem ) plays a role in the hydraulic strategy of tropical‐subtropical woody plants remains unclear. We investigated 12 key hydraulically related traits of stems and leaves (i.e. cavitation resistance, water potential, safety margin, vulnerability segmentation, leaf‐sapwood area ratio and water use efficiency) and mortality rates for 130 dominant woody species from six forest types with a range of aridity index in tropical–subtropical China. Our main objectives were to: (1) build a stem‐leaf hydraulic framework and capture the key hydraulic traits, (2) compare the hydraulic strategies of different forest types and functional groups and (3) elucidate the influence of environmental factors and hydraulic traits on mortality rate. Trait network analysis revealed close relationships among stem and leaf hydraulic traits, where cavitation resistance, turgor loss point and P 50 leaf–stem were the key traits. In general, a larger P 50 leaf–stem was associated with lower minimum water potential, leaf hydraulic safety margin and leaf‐sapwood area ratio but higher wood density, stem hydraulic safety margin and water use efficiency. Tropical forest (high aridity) had higher leaf embolism resistance, P 50 leaf–stem , wood density and water use efficiency than subtropical forest (low aridity), while shrubs showed higher leaf embolism resistance and more negative turgor loss point than trees. However, stem‐leaf hydraulic strategy did not differ significantly between evergreens and deciduous. Both aridity index and hydraulic traits affect species mortality. Particularly, P 50 leaf–stem was a good predictor of drought‐induced mortality in tropical forests. Synthesis . Our results recommend that vulnerability segmentation should be incorporated into the hydraulic strategy of tropical–subtropical woody plants to explore their drought response to future climate change.