Differential Responses Of Female And Male Seedlings Of Populus Euphratica To Drought,Salt And Alkali Stress

There have been many reports on the response of dioecious plants to environmental stress in the context of increased soil drought and salinity exacerbation due to climatic or anthropogenic disturbances,but the interaction between stress factors is rarely considered.In addition,there are fewer studies on sexual dimorphism in tree species from arid and semi-arid regions of northwestern China.Populus euphratica,a typical dioecious plant,grows mainly in arid and semi-arid regions and is characterized by high resistance to stress.This study focuses on the response of P.euphratica to drought and salt stress,and salt and alkali stress;in addition to the differential response to stress between male and female,and reveals further changes in this difference under different interactive stresses.The results of this study provide an important theoretical basis for the ecological restoration,afforestation and conservation of P.euphratica forests.The main results are as follows:（1）Different adaptive strategies of female and male P.euphratica to drought,salt stress and their interactionsIn this study,the growth and anatomy,gas exchange,water and nitrogen utilization,accumulation of reactive oxygen species（ROS）and osmoregulation of female and male seedlings of P.euphratica under drought,salt and interactive stresses were determined.The results indicated that there were no significant differences between the traits studied in the female and male P.euphratica under control conditions.However,the males of P.euphratica showed protective structure and significantly higher biomass or net photosynthetic rate（P_n）,higher water and nitrogen use,higher osmoregulation and ROS scavenging ability or lower leaf Cl^–content under stress conditions（p<0.05）.The interactions of sex×drought×salt significantly affected the biomass,P_n,water and nitrogen use,superoxide radicals（O₂^–）,proline and free amino acid（FAA）of P.euphratica seedlings（p<0.05）.In summary,this study found that sex differentiation depended on stress gradients,implying differences in adaptive responses and life strategies between female and male P.euphratica under stress conditions,and that males had stronger resistant to drought,salt and interactive stresses than females.（2）Differential responses of female and male P.euphratica under salt,alkali and combined stressThis research measured plant growth and morphology,leaf stomata,gas exchange,carbon stable isotope(δ¹³C),total soluble sugar and starch content,Na⁺accumulation and allocation,oxidative stress and antioxidants of female and male P.euphratica seedlings in response to salt,alkali and their interaction.The results showed that no significant sex-differences were observed in the traits studied under control conditions.In addition,compared with males of P.euphratica,the females showed significantly greater inhibitory and negative effects,such as greater decrease in growth and gas exchange,lower stomatal density and water use efficiency(δ¹³C),and lower soluble sugar and antioxidant enzyme activities under salt,alkali and the interactive stress（p<0.05）.Furthermore,the males of P.euphratica had significantly greater ability to restrict Na⁺transport（p<0.05）.For instance,males allocated significantly higher Na⁺contents in stems and roots than females,whereas females had significantly higher Na⁺contents in leaves under stress conditions（p<0.05）.In conclusion,the males of P.euphratica had more strong resistance than females under salt,alkali and their interactive stress.