Divergent root water uptake depth and coordinated hydraulic traits among typical karst plantations of subtropical China: Implication for plant water adaptation under precipitation changes

Plantations, as a form of vegetation restoration, play a critical role in the recent greening of the earth. However, the sustainability of the restored vegetation under precipitation changes has rarely been estimated, largely because of a lack of knowledge about the related plant water adaptation. In the current study, six tree species, including evergreen and deciduous, were selected from a typical karst forest types in Southwest China, a hotspot of earth greening. Root water uptake depth and hydraulic-related traits of stem and leaf were studied. Our results showed that, in the wet season, the evergreen species mainly rely on soil water sources from a depth of 0–30 cm (49.74%), while the deciduous use deeper layers of 30–70 cm in depth (47.58%). In the dry season, the deciduous species shed their leaves while the evergreens utilized soil water at a depth of 0–10 cm with an average absorption of 66.96%. The evergreen species exhibit higher xylem-cavitation resistance (reflect by P50) and leaf-turgor maintenance capacity (reflect by Ψtlp) than the deciduous. The significant correlations between plant water uptake depth and water potential, and hydraulic traits and water uptake depth indicate the different water adaptation strategies of evergreen and deciduous. In detail, evergreen species that rely on shallower water sources exhibit a larger diurnal range of leaf water potential, more xylem-cavitation resistant and leaf-turgor maintenance capacity. In contrast, deciduous species, with deeper water uptake, show narrower diurnal range of leaf water potential with lower drought resistance of stem and leaves. Our results highlight the probable divergent response (such as growth restriction and hydraulic failure) of evergreen and deciduous plantation tree species to the changing precipitation patterns under climate change.