Populus euphratica males exhibit stronger drought and salt stress resistance than females

Much attention has been paid on dioecious plants and their responses to environmental stresses. However, little information is available on sexual dimorphism in Populus euphratica Oliver, which usually grows in arid desert areas and exposes to drought and salinity stress. In this study, we investigated female and male seedlings of P. euphratica and their growth and anatomical structure, gas exchange, water and nitrogen use, oxidative stress and antioxidants under drought, salinity, and the combined stress. We found that there were no significant sexual differences in P. euphratica under control conditions (well-watered and no salt addition). However, males showed stronger resistance to drought, salinity and especially to the combined stress, as they had protective structures, higher biomass, net photosynthetic rate (Pn), water and nitrogen use, osmotic adjustment and reactive oxygen species (ROS) scavenging ability, and a lower leaf Cl– content under stress conditions. The significant sex × drought × salinity interactions for biomass, Pn, water and nitrogen use, superoxide radicals (O2–), proline and free amino acids (FAA) indicated that sexual dimorphism occurs depending on the stress gradients, implying contrasting adaptive responses and life strategies in P. euphratica females and males under stress conditions. Due to the sexual dimorphism of P. euphratica under drought and salinity stress, more severe shifts in the sex ratio of P. euphratica forests may occur under future climate change with aggravated aridity and soil salinity.