Sex-specific responses of Populus deltoides to combined salinity and calcium under waterlogging conditions

In this study, we investigated the sex-specific ion uptake and physiological and biochemical responses to combined salinity and calcium treatments of male and female Populus deltoides under waterlogging conditions. Results indicate that both P. deltoides clones were sensitive to salinity and calcium. Under well-watered conditions, salinity stress could especially increase the Na content in female P. deltoides clones, whereas salinity and calcium could increase the K and Ca content in male clones. Waterlogging could evidently stimulate Na content in leaves under salinity, especially in female P. deltoides clones. However, waterlogging had no visible effects on the amount of Ca absorption between the two clones under abundant calcium conditions. The physiological and biochemical responses to combined salinity and calcium exceeded the effects of salinity or calcium individually. However, no significant difference was observed, hence indicating the similar responses of male and female P. deltoides clones. The lower Na content and Na:Ca ratio, and the higher K and Ca content in male clones suggest that the male clones could maintain ion homeostasis better than the female clones. The sex-specific differences in net photosynthetic rate, intercellular CO2 concentration, effective quantum yield of photosystem II, photochemical quenching coefficient, non-photochemical quenching coefficient, photosynthetic electron transport rate, content of superoxide anions, hydroxyl radicals, H2O2, soluble protein, and activities of superoxide dismutase under certain conditions suggest that female P. deltoides clones are more sensitive to salinity, calcium, and the combination of both than their male counterparts.