Older Quercus aliena stands have a more flexible water absorption strategy than younger counterparts

The water absorption strategies of trees exert crucial roles in shaping forest productivity. As global precipitation changes, older trees in response to water stress may be different to younger trees. Hence, it is essential to explore the water absorption of different stand-aged trees for predicting their growth status under the changes in precipitation pattern. Up to now, the water absorption strategies between older and younger trees responding to different magnitudes of precipitation remain unclear. Here, we used the δD and δ18O connected with Bayesian mixture model (MixSIAR) to calculate the water absorption strategies of Quercus aliena stands growing for 40−60 years, 60−90 years, 120−150 years and >150 years following three precipitation events (7.4, 19.6 and 30.1 mm). We found no difference in the water absorption of Q. aliena among these four different aged forests after small precipitation (7.4 mm). By comparison, under moderate (19.6 mm) and heavy (30.1 mm) precipitation, the ratios of water absorption from the topsoil (0−20 cm) by 60−90 years (48.6 ± 3.4%), 120−150 years (30.4 ± 6.6%) and >150 years (53.6 ± 7.6%) of Q. aliena stands were significantly higher than those growing for 40−60 years (15.2 ± 1.5%) based on one-way ANOVA, while the opposite pattern appeared in the subsoil layers (20−100 cm). Furthermore, the structural equation model showed that root biomass primarily drove the water absorption strategies of Q. aliena. These findings imply that older Q. aliena stands exhibit more flexible water absorption strategies than their relatively younger counterparts following different precipitation, reflecting their stronger adaptability to the changed climate.