Evidence of foliar water uptake in a conifer species

Foliar water uptake (FWU) is the main mechanism used by herbaceous plants in arid areas to absorb small amounts of precipitation. It has an important ecological and hydrological effect for alleviating plant drought stress. However, it is unknown whether woody plants can absorb water through the leaves when water absorption via roots is insufficient. This study explored whether FWU exists and the FWU conditions in semi-humid rock mountainous areas. Isotopes were labeled to detect FWU under different soil water content (SWC) gradients (3.9–6.5%, 6.5–9.1%, 9.1–15.6%, 15.6–20.8%, and 20.8–26.0%) and different precipitation gradients (1 mm/h, 5 mm/h, 10 mm/h, and 15 mm/h) in simulated precipitation experiments with indoor potted plants. The results showed that FWU occurred in each treatment if the SWC ≤ 21.9% no matter the precipitation amount. Water absorption via FWU increased with the increase of precipitation intensity but decreased with the increase of SWC. The greatest ratios of FWU were 2.77% and 9.52% of precipitation intensity of 1 mm/h and 15 mm/h, respectively, in the 3.9–6.5% treatment. The precipitation absorbed by the leaves can be transported to the xylem or root system along the water potential gradient of leaves–branches–roots. The precipitation with reverse migration in branches and roots increased with the increase of the water potential gradient of leaves–branches–roots. These findings suggest that Platycladus orientalis can uptake water through roots and leaves, effectively alleviating drought stress. This study provides new insights into water use patterns and water migration in trees.