Quantifying Cunninghamia lanceolata Foliar Water Uptake and Reverse Transport Provides a New Approach to Improving Drought Tolerance

Foliar water uptake (FWU), an important source of supplemental water for plants, provides a novel pathway for alleviating drought stress. However, quantitative analysis of reverse water transport after water uptake in plant leaves has been insufficient, which has become a bottleneck in the study of adaptive plant survival under drought stress. This study investigates Cunninghamia lanceolata ( C. lanceolata ) using pot experiments with controlled watering, simulated fog environments, and stable isotope techniques to quantitatively explore the conditions that facilitate water absorption in C. lanceolata seedlings under drought stress, the thresholds for reverse water movement in various organs, and whether FWU enhances drought resistance. The results indicated that FWU occurred when the soil water content (SWC) fell below 60% of field capacity for 2 h in a foggy water environment. After 12 h of fog water treatment, the leaf water potential (LWP) and leaf water content (LWC) of C. lanceolata seedlings significantly improved under drought stress. When SWC exceeded 60% of field capacity, retrograde transport did not occur. When SWC ranged between 45% and 60% of field capacity, leaf water uptake retrograde transport to the stem, resulting in an increase in δ D value by 20.54‰ ± 5.16‰. When SWC dropped between 30% and 45% of field capacity, retrograde transport to the rhizosphere soil occurred, with δ D values increasing by 30.94‰ ± 1.4‰. Water absorbed by leaves can move along the leaf‐stem‐root water potential gradient into the xylem and surrounding soil, with maximum utilization rates of 16.26%, 11.13%, and 1.66%, respectively, thereby improving the plant's water status. From the above, it can be seen that C. lanceolata can effectively alleviate drought stress through leaf water uptake, and the reverse water transport threshold can be used as a research basis to provide new ideas for plants to cope with drought stress.