Differences in ecophysiological responses of Populus euphratica females and males exposed to salinity and alkali stress

Soil salinity is usually accompanied by alkalization in northwest China, and they both negatively impact plant growth and result in severe ecological problems. Some studies have reported tree responses to salinity or alkali stress alone, however, the interactive salinity and alkali effects are still unclear, especially in dioecious trees. In this study, we measured growth, morphology, leaf stomata, gas exchange, carbon isotope composition (δ13C), total soluble sugar and starch contents, Na+ accumulation and allocation, oxidative stress, and antioxidants of female and male Populus euphratica seedlings in response to salinity, alkali and their interaction. Our study showed no significant sexual differences in studied traits under control conditions. In addition, P. euphratica females showed greater inhibitory and negative effects, such as bigger decreases in growth and gas exchange, lower stomatal density and water use efficiency (as described by δ13C), and lower levels of soluble sugars and antioxidant enzyme activities compared with males under salinity, alkali and interactive stress conditions. Furthermore, P. euphratica males had a greater ability of ion exclusion and Na + transport restriction. For example, males allocated more Na+ to stems and roots than females, whereas females had higher Na+ contents in leaves under stress conditions. In conclusion, our results indicated that P. euphratica males have superior resistance and they perform better than females under salinity, alkali and their interactive stress conditions.