The response of reactive oxygen generation and scavenging has been studied in the leaves of annual Robinia pseudoacacia seedlings under manipulated nitrogen fertilizer and water supply.The results showed that:(1)At a constant nitrogen level,reduction of soil moisture decreased the content of total biomass and photosynthetic pigments ,elevated levels of hydrogen peroxide (H₂O₂);also with lessened water supply,the activities of superoxide dismutase (SOD),peroxidase (POD) and catalase (CAT) in antioxidant enzyme system all reduced;while contents of ascorbic acid (ASA) and glutathione (GSH) in antioxidant both increased;MDA content increased gradually and companying the relative conductivity significantly increased.(2)Then under the same water supply condition,improved soil nitrogen levels dramatically increased photosynthetic pigment content as well as the total biomass but significantly reduced the H₂O₂ content;it also enhanced the activities of SOD,POD,and CAT to different degrees;still with more available nitrogen,ASA content and GSH content declined,respectively;the content of MDA and the relative conductivity showed a reduction.In conclusion,the increasing of soil nitrogen content could significantly improve the content of photosynthetic pigments and inhibit the generation of reactive oxygen;it also increase the total biomass,enhance the activities of antioxidant enzymes to a certain extent,reduce the degree of cell membrane-lipid peroxidation.These responses are helpful to alleviate the drought-induced injury to the plants.