Quantifying interspecific variations of tree resilience to drought and revealing the underlying mechanisms are of great importance to the understanding of forest functionality particularly in water-limited regions with foreseeable increase in temperature and the associated drought stress. So far, comprehensive studies incorporating investigations in interspecific variations of long-term growth patterns of trees and the underlying physiological mechanisms are very limited. Here, in a semi-arid site of northern China, tree radial growth rate, inter-annual tree-ring growth responses to climate variability, as well as physiological characteristics pertinent to xylem hydraulics, carbon assimilation and drought tolerance were analyzed in seven pine species growing in a common environment. Considerable interspecific variations in radial growth rate, growth response to drought and physiological characteristics were observed among the studied species. Higher hydraulic efficiency is related to greater photosynthetic capacity but not higher tree radial growth rate. Rather, radial growth of species with higher hydraulic conductivity and photosynthetic capacity was more sensitive to drought stress that is at least partially due to a trade-off between hydraulic efficiency and safety across species. This study thus demonstrates the importance of drought resilience rather than instantaneous water and carbon flux capacity in determining tree growth in water-limited environments.

The hydraulic vulnerability segmentation hypothesis proposes that plant branches are more resistant to cavitation than roots, namely, the difference in vulnerability to cavitation between branches and roots is positive ( P 50 root - branch > 0). However, it is not clear how this phenomenon can vary along environmental aridity gradients. We compiled the above hypothesis with 105 woody species from four biomes with increasing aridity, by compiling functional traits related to hydraulic properties and anatomical structures of branches and roots. We investigated the relationships between P 50 root - branch and several environmental factors that are associated with aridity. We found a positive P 50 root - branch across species, which supported the hydraulic vulnerability segmentation hypothesis, and P 50 root - branch increased significantly with environmental aridity. Branch xylem hydraulic conductivity changed from “more efficient” (e.g., wider conduit, higher hydraulic conductivity) to “safer” (e.g., narrower conduit, more negative P 50) in response to increased aridity, while root xylem hydraulic conductivity remained unchanged across aridity gradients. Our results demonstrated that hydraulic vulnerability segmentation is more pronounced for species from arid regions. Changes in branch traits may be responsible for hydraulic vulnerability segmentation between branches and roots.