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 (Pn), transpiration (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), light
saturation point (LSP), apparent quantum yield (Ф),carboxylation efficiency (CE), light-saturated photosynthetic rate (Pmax), maximum efficiency of PSII (Fv/Fm) and maximum effective quantum yield of PSII (Yield), and increased the total chlorophyll concentration (TC), CO2 compensation point (Г), non-photochemical quenching coefficient, peroxidase (POD) activity and carbon isotope composition (δ13C).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), Pn, E, gs,Ci, LSP,, CE, Pmax, Fv/Fm,photochemical quenching coefficient, POD activity and δ13C,but a lower SLA, chlorophyll a/b ratio, carotenoids/total chlorophyll ratio and Гthan females. However, Caro, Lsp,Г,Ф, 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.