Reciprocal grafting separates the roles of the root and shoot in sex-related drought responses in Populus cathayana males and females.

Drought stress responses and sensitivity of dioecious plants, such as Populus cathayana Rehd., are determined by different mechanisms in each sex. In general, males tend to be more resistant while females are more sensitive. Here, we used reciprocal grafting between males and females to determine the relative importance of roots and shoots when plants are exposed to drought stress. Total dry matter accumulation (DMA), photosynthetic capacity, long-term water-use efficiency (Δ), water potential and ultrastructure of mesophyll cells were evaluated to determine the different roles of root and shoot in sex-related drought responses. Plants with male roots were found to be more resistant and less sensitive to water stress than those with female roots under drought conditions. On the contrary, plants with female shoots grew better than those with male shoots under well-watered conditions. These results indicated that the sensitivity of males and females to water stress is primarily influenced by root processes, while under well-watered conditions sexual differences in growth are primarily driven by shoot processes. Furthermore, grafting female shoot scion onto male rootstock was proved to be an effective mean to improve resistance to water stress in P. cathayana females.