Stem hydraulic conductivity and embolism resistance of Quercus species are associated with their climatic niche

The hydraulic traits of a plant species may reflect its climate adaptations. Southwest China is considered as a biodiversity hotpot of the genus Quercus (oak). However, the hydraulic adaptations of Asian oaks to their climate niches remain unclear. Ten common garden-grown oak species with distinct natural distributions in eastern Asia were used to determine their stem xylem embolism resistance (water potential at 50% loss of hydraulic conductivity, P50), stem hydraulic efficiency (vessel anatomy and sapwood specific hydraulic conductivity (Ks)) and leaf anatomical traits. We also compiled four key functional traits: wood density, hydraulic-weighted vessel diameter, Ks and P50 data for 31 oak species from previous literature. We analyzed the relationship between hydraulic traits and climatic factors over the native ranges of 41 oak species. Our results revealed that the 10 Asian oak species, which are mainly distributed in humid subtropical habitats, possessed a stem xylem with low embolism resistance and moderate hydraulic efficiency. The deciduous and evergreen species of the 10 Asian oaks differed in the stem and leaf traits related to hydraulic efficiency. Ks differed significantly between the two phenological groups (deciduous and evergreens) in the 41-oak dataset. No significant difference in P50 between the two groups was found for the 10 Asian oaks or the 41-oak dataset. The oak species that can distribute in arid habitats possessed a stem xylem with high embolism resistance. Ks negatively related to the humidity of the native range of the 10 Asian oaks, but showed no trend when assessing the entire global oak dataset. Our study suggests that stem hydraulic conductivity and embolism resistance in Quercus species are shaped by their climate niche. Our findings assist predictions of oak drought resistance with future climate changes for oak forest management.