Populus cathayana males exhibit more efficient protective mechanisms than females under drought stress

The effects of three watering regimes (100%, 50% and 25% of field capacity, FC) on photosynthetic traits and leaves’ self-protective systems were investigated in Populus cathayana Rehd. males and females. The results showed that drought (25% of FC) caused disorder in photosynthesis, increased the amounts of osmotically active substances (soluble sugars, proteins and proline), accumulation of reactive oxygen species (ROS), changes in antioxidant enzyme activities and damage in the integrity of cellular membranes and chloroplasts in both males and females. However, compared with drought-stressed females, drought-stressed males showed (1) higher values of net photosynthetic rate (Pn), maximum rate of electron transport driving RuBP regeneration (Jmax), maximum rate of RuBP carboxylation (Vcmax), carboxylation efficiency (CE) and non-photochemical quenching coefficient (qP); (2) higher contents of soluble proteins and proline; (3) higher activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) and polyphenoloxidase (PPO); (4) less negative effects on cellular membranes and chloroplasts. These results indicate that P. cathayana males have a better self-protection of the photosynthetic system, greater accumulation of substances for osmotic adjustment and a more efficient enzymatic detoxification cycle for eliminating the negative effects caused by ROS under drought stress than do females.