Drought inhibits photosynthetic capacity more in females than in males of Populus cathayana

We investigated sex-related photosynthetic responses to drought in the dioecious species, Populus cathayana Rehd, Plants were subjected to two watering regimes (100% and 30% of field capacity) in a semi-controlled environment. Drought significantly decreased leaf area (LA), total number of leaves (TNL), specific leaf area (SLA), relative water content, net photosynthetic rate (P-n), transpiration (E), stomatal conductance (g(s)), intercellular CO2 concentration (C-i), light saturation point (L-SP), apparent quantum yield (Phi), carboxylation efficiency (CE), light-saturated photosynthetic rate (P-max), maximum efficiency of PS Pi (F-v/F-m) and maximum effective quantum yield of PS Pi (Yield), and increased the total chlorophyll concentration (TC), CO2 compensation point (Gamma), non-photochemical quenching coefficient, peroxidase (POD) activity and carbon isotope composition (delta C-13). Moreover, differences between males and females were detected in many of these responses. In the drought treatment, males exhibited significantly higher LA, TNL, TC, concentration of carotenoids (Caro), P-n, E, g(s) C-i, L-SP, Phi, CE, P-max, F-v/F-m, photochemical quenching coefficient, POD activity and VC, but a lower SLA, chlorophyll a/b ratio, carotenoids/total chlorophyll ratio and F than females. However, Caro, L-SP, Gamma, Phi, CE and POD activity were apparently associated with sex-related resource demands, because significant differences in these traits were detected between the sexes under well-watered conditions. Our results indicate that drought stress limits photosynthetic capacity more in females than in males.