Effect of NaCl Stress on Gas Exchange and Chlorophyll Fluorescence of Cucumis melo Seedlings

Muskmelon seedlings,cv.Huanghemi and Baishami,were employed to study the effect of NaCl stress on photosynthesis,chlorophyll contents and chlorophyll fluorescence parameters.The results indicated that net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),maximum photochemical efficiency of PSⅡ(Fv/Fm),potential activity of PSⅡ(Fv/Fo),quantum efficiency of non-cyclic electron transport of PSⅡ(ΦPSⅡ) and photochemical quenching(qP) decreased,while non-photochemical quenching(qN) increased under NaCl stress,especially under high concentrations in both varieties.When NaCl concentration was ≤50 mmol·L-1,intercellular CO2 concentration(Ci) decreased,while stomatal limitation value(Ls) increased.In contrast,Ci increased but Ls decreased when NaCl concentration was ≥100 mmol·L-1.The results indicated that photosynthesis of muskmelon was limited by stomatal factor under slight NaCl stress,but mainly by non-stomatal factors under severe NaCl stress.