Dioecious plant species represent an important component of terrestrial ecosystems. Yet, little is known about sex‐specific responses to drought and elevated temperatures. Populus cathayana Rehd, which is a dioecious, deciduous tree species, widely distributed in the northern, central and southwestern regions of China, was employed as a model species in our study. In closed‐top chamber experiments, sex‐specific morphological, physiological and biochemical responses of P. cathayana to drought and different elevated temperatures were investigated. Compared with the controls, drought significantly decreased the growth and the net photosynthesis rate (A), and increased the intrinsic water use efficiency (WUE_i), carbon isotope composition (δ¹³C), and the malondialdehyde (MDA) and abscisic acid (ABA) contents in droughted plants. In contrast, elevated temperatures significantly promoted the growth and the A, but decreased the WUE_i, δ¹³C, MDA and ABA contents in well‐watered individuals. When compared with males, elevated temperatures induced well‐watered females to express a greater increase in the height growth (HG), basal diameter (BD), leaf area (LA), total number of leaves (TNL), dry matter accumulation (DMA) and specific leaf area (SLA), and a lower decrease in the A value, transpiration (E), stomatal conductance (g_s), MDA and ABA contents, while elevated temperatures induced drought‐stressed females to exhibit lower values of HG, BD, LA, TNL, DMA, A, E, g_s and the intercellular CO₂ concentration (C_i), and higher levels of SLA, WUE_i, δ¹³C, MDA and ABA contents. Our results indicated that the female individuals of P. cathayana are more responsive and suffer from greater negative effects than do males when grown under environments with increased drought stress and elevated temperature.

The young, vegetatively propagated cuttings of Populus cathayana Rehder were exposed to a progressive drought stress for 12 weeks in a greenhouse to characterize the physiological and biochemical basis of drought adaptation in woody plants. Two contrasting populations were employed in our study, which were from the wet and dry climate regions in western China, respectively. The results showed that the adaptive responses of P. cathayana to drought were affected by drought intensity and poplar genotype (population). The progressive drought stress significantly inhibited plant growth, increased carotenoid contents and, at the same time, accumulated soluble sugars and free proline in the plants of both populations tested. On the other hand, the gradually increasing drought also induced antioxidative systems including the increase of the activities of superoxide dismutase (SOD) and guaiacol peroxidase (POD). Moreover, there were different responses to progressive drought stress between the two contrasting populations. Compared with the wet climate population, the dry climate population had lower shoot height and growth rate, higher free proline content, and more efficient photoprotective system (such as higher carotenoid content and Car/Chl) and antioxidant system (such as higher POD activity), as a result of drought stress. These results suggest that the dry climate population possesses better drought tolerance than the wet climate population. The differences in drought tolerance may be closely related with efficient photoprotective system, accumulation of the osmoprotectant proline as well as the increased capacity of the antioxidative system to scavenge reactive oxygen species, and the consequent suppressed level of lipid peroxidation under drought conditions.