Foliar Water Uptake and Its Relationship with Photosynthetic Capacity and Anatomical Structure between Female and Male Populus euphratica at Different Growth Stages

Foliar water uptake (FWU) is considered to be a common phenomenon in most terrestrial plants. As a supplementary water source, it plays an important role in the growth and survival of plants in arid areas. However, there is no research to explain the water absorption of plant leaves from the perspective of gender specificity. To this end, we carried out a leaf water absorption capacity experiment and in situ wetting field experiment, respectively, in the early (Initial), middle (Mid) and end (End) of the growth season of male and female Populus euphratica. The results of the leaf water absorption capacity experiment showed that the FWU capacity of male and female P. euphratica showed an increasing trend with the growth period and reached the maximum at the End period. The FWU capacity of female P. euphratica was significantly greater than that of male P. euphratica after the Initial stage. The water absorption speed (k) of male and female leaves also increased with the growth period, but the increase was not significant. The increase in leaf water content per mg of water absorbed per unit of leaf area (LWCA) of male P. euphratica was always greater than that of female P. euphratica. Specific leaf area (SLA), leaf water saturated deficit (WSD) and water absorption parameters (FWU capacity, k) were significantly correlated. The results of the in situ wetting field experiment show that humidification significantly increased the predawn water potential (Mid period) of female and male P. euphratica leaves and the net photosynthetic rate (Mid period) of male P. euphratica leaves, but had no significant effect on chlorophyll fluorescence parameters and anatomical structure. The MFA results show that the water status of male and female P. euphratica leaves was significantly correlated with photosynthetic parameters, fluorescence parameters and anatomical parameters. Our results show that the foliar water uptake capacity of female P. euphratica leaves was stronger than that of male P. euphratica and shows significant dynamic changes during the growing season. This was because female P. euphratica has a developed water storage structure. Foliar water uptake can effectively improve the water status and photosynthetic capacity of male and female P. euphratica, and this improvement was more significant during the most intense period of soil water stress. These findings will deepen our understanding of the ecological adaptation of dioecious plants to foliar water uptake.