Abstract: Uneven spatial and temporal distribution of precipitation pattern induced by global climate change has caused the increasingly serious periodic drought of monsoon climate in subtropical regions. Water uptake of leaves plays important ecological and hydrological roles in alleviating drought stress. In this study, potted Chinese fir (Cunninghamia lanceolata) was sprayed with heavy water (δD) to simulate precipitation. We conducted a continuous monitoring on utilization ratio of water absorption and reverse migration of Chinese fir leaves under four soil moisture levels (naturally abundant, naturally suitable, slightly dry, moderately dry; the corresponding actual soil water content (SWC) was 21%-26%, 16%-21%, 12%-16%, and 8%-12%, respectively) and four durations of leaf wetting (10, 30, 40, and 60 min). The results showed that under drought stress (SWC 8%-16%) and when the duration of leaf wetting was ≥ 30 min, foliar water uptake occurred across all soil moisture treatments, and water absorbed by leaves could be reversely transported to the xylem and soil near roots along the leaf-branch-root water potential gradient, which can improve water status of plants. The proportion of leaf utilization of reversely transported heavy water gradually decreased with the increases of time after the end of simulated precipitation, and reached the maximum value of 10.82% one hour after precipitation. The utilization ratio of reversely transported heavy water by branches and roots firstly increased and then decreased slowly with the increases of time after the precipitation; the utilization ratio reached the maximum value of 8.36% and 0.65% after 2 h and 2-4 h after the precipitation, respectively. These results indicate that the response time of different parts of C. lanceolata is different and that there is a certain lag in the utilization ratio of reversely transported heavy water. Therefore, C. lanceolata can absorb water through leaves and roots, which is of great significance to effectively utilize natural water resources and alleviate drought stress in seasonally dry regions.

Key words: drought stress, foliar water uptake, isotope labeling method, water use efficiency.