Sex-specific responses of Populus yunnanensis exposed to elevated CO2 and salinity.

Populus yunnanensis Dode., a native dioecious woody plant in southwestern China, was employed as a model species to study sex-specific morphological, physiological and biochemical responses to elevated CO2 and salinity. To investigate the effects of elevated CO2 , salinity and their combination, the cuttings were exposed to two CO2 regimes (ambient CO2 and double ambient CO2 ) and two salt treatments in growth chambers. Males exhibited greater downregulation of net photosynthesis rate (Anet ) and carboxylation efficiency (CE) than females at elevated CO2 , whereas these sexual differences were lessened under salt stress. On the other hand, salinity induced a higher decrease in Anet and CE, more growth inhibition and leaf Cl(-) accumulation and more damage to cell organelles in females than in males, whereas the sexual differences in photosynthesis and growth were lessened at elevated CO2 . Moreover, elevated CO2 exacerbated membrane lipid peroxidation and organelle damage in females but not in males under salt stress. Our results indicated that: (1) females are more sensitive and suffer from greater negative effects than do males under salt stress, and elevated CO2 lessens the sexual differences in photosynthesis and growth under salt stress; (2) elevated CO2 tends to aggravate the negative effects of salinity in females; and (3) sex-specific reactions under the combination of elevated CO2 and salinity are distinct from single-stress responses. Therefore, these results provide evidence for different adaptive responses between plants of different sexes exposed to elevated CO2 and salinity.