Abstract: With water culture,this paper studied the effects of NO₃^- stress and recovery on the chlorophyll contents,chlorophyll fluorescence parameters,and ATPase activities of cucumber seedling leaves.The results showed that under stress for 7 days,the chlorophyll a,chlorophyll b,total chlorophyll and carotenoid contents,intrinsic fluorescence (F_o),and MgATPase and Ca-ATPase activities were increased significantly when the NO₃^- concentration was high (168 mmol ·L^-1),while the intrinsic photochemical efficiency (F_v/F_m),potential activities (F_v/F_o) and quantum yield (ΦPSⅡ) of PSⅡ were decreased with increasing NO₃^- concentration.After recovery for 7 days,the chlorophyll and carotenoid contents of all treatments with NO₃^- were lower than CK,while the intrinsic fluorescence,intrinsic photochemical efficiency and quantum yield of PSⅡ were similar to CK when the NO₃^- concentration was ≤ 84 mmol·L^-1,and the F_v/F_m and ΦPSⅡ were significantly lower than CK when the NO₃^- concentration was>84 mmol·L^-1.The potential activity of PSⅡ was similar to CK when the NO₃^- concentration was 42 and 126 mmol·L^-1,but significantly lower than CK in other treatments.The activities of Mg-ATPase and Ca-ATPase were decreased firstly but increased then when the NO₃^- concentration was>84 mmol·L^-1.

Key words: snow pack, global warming, soil temperature, soil nutrient, alpine forests of west Sichuan