Objective We examined the seedling foliar water absorption characteristics of 8 tree species and their physiological responses to fog water in Xishuangbanna region of southwestern China, which will provide references for the tropical rainforest conservation and regional water resource management.

Method This study focused on 8 common tree seedlings. The leaf water absorption capacities of seedlings were evaluated through an immersion experiment. Using the hydrogen isotope (δ²H) labeling technique and indoor fog water simulation experiments, this study revealed the fog water absorption characteristics of tree seedlings by comparing the δ²H differences in plant leaves between control group (i.e., without fog water) and the experimental group (i.e., with fog water). Meanwhile, we measured the gas exchange characteristics of seedling leaves, including net photosynthesis rate, stomatal conductance, transpiration rate, and leaf water potential to analyze the physiological responses of the test plants to fog water.

Result (1) The foliar water absorption per unit area of all tree seedlings ranged from 0.32 to 0.91 mg/cm². The ranking order of their water absorption capacities was as follows: Ficus curtipes, Pometia pinnata, Ficus racemosa, Streblus asper, Erythrina subumbrans, Dipterocarpus turbinatus, Terminalia myriocarpa, and Parashorea chinensis. (2) In the environment without fog water, the δ²H of leaf water in control group for all seedlings increased by 0.7‰ to 16.60‰ after the experiment. In the simulated fog water environment (with δ²H ranging from −143.78‰ to −140.31‰), the δ²H of leaf water in the experimental group for all seedlings decreased by 3.08‰ to 19.24‰. (3) Before and after the experiment, the net photosynthetic rate of seedling leaves in the control group without fog water increased; in contrast, the increase was smaller in the fog-water-treated group. Conversely, the leaf water potential of seedlings in control group decreased, while the leaf water potential increased in the experimental group. The changes in leaf water potential were significantly negatively correlated with leaf water δ²H.

Conclusion Leaves of all eight tree species show foliar water uptake, and isotope labeling further confirms that they can directly absorb fog water. Across species, leaf water absorption capacity and fog-water uptake are tightly coupled. Compared with the fog-free control, fog application reduces the increment in net photosynthetic rate of seedling leaves, yet significantly raises leaf water potential via fog-water uptake, thereby improving the plant’s water status.