Abstract[Objective]This study to aimed to investigate the effects of Cu stress on root exudates and microbial activities in rhizosphere of grafted and ungrafted cucumber seedlings,and therefore to elucidate the microbial mechanism of grafting for increasing cucumber plants tolerance to Cu stress[Method]Four treatments:(1)ungrafted seedlings+test soil(U0);(2)ungrafted seedlings+test soil+CuSO4·5H2O(U1);(3)grafted seedlings+test soil(G0);(4)grafted seedlings+test soil+CuSO4·5H2O(G1)were set in the pot culture experiment.The contents of free amino acids,organic acids,phenolic acid and sugars,microbial population and enzyme activity in the four treatment were measured,respectively.[Result]The secretion of amino acids and organic acids were increased under Cu stress.The amino acids secretions of grafted seedlings roots were obviously higher than ungrafted seedlings except for Phe and Val.At the same time,the secretion of oxalic acid,malic acid,acetic acid,citric acid,cinnamic acid,ρ-hydroxybenzoic acid and benzoic acid of grafted seedlings were significantly higher than ungrafted seedlings as well.Therefore,more Cu2+were restricted in soil by chelating,complexing and precipitation with root exudates,and its toxicity was decreased.The soil microbial biomass C and N in grafted cucumber rhizosphere were significantly higher than those in ungrafted cucumber rhizosphere,whereas basal respiration and metabolic quotient were significantly lower.Under Cu stress,the numbers of actinomyces and nitrogen fixing bacteria decreased and the number of fungi increased significantly,whereas there was no significant difference in amounts of bacteria.The numbers of bacteria,actinomyces,and nitrogen fixing bacteria in grafted cucumber rhizosphere were significantly higher than those in ungrafted cucumber rhizosphere,but the number of fungi was opposite.The activities of soil urease,phosphatase,sucrase and catalase in grafted cucumber rhizosphere were significantly higher than those in ungrafted cucumber rhizosphere.[Conclusion]These indicated that the soil microbial environment and soil enzymes activities were improved by grafting under Cu stress,and as a result,the adaptability of cucumber to Cu stress was improved. Abstract [Objective] This study to aimed to investigate the effects of Cu stress on root exudates and microbial activities in rhizosphere of grafted and ungrafted cucumber seedlings, and therefore to elucidate the microbial mechanism of grafting for increasing cucumber plants tolerance to Cu stress [Method] Four treatments: (1) ungrafted seedlings + test soil (U0); (2) ungrafted seedlings + test soil + CuSO4-5H2O (U1); (3) grafted seedlings + test soil soil + CuSO4 · 5H2O (G1) were set in the pot culture experiment. The contents of free amino acids, organic acids, phenolic acid and sugars, microbial population and enzyme activity in the four treatment were measured, respectively. of amino acids and organic acids were increased under Cu stress. The amino acids secretions of grafted seedlings roots were obviously higher than ungrafted seedlings except for Phe and Val. At the same time, the secretion of oxalic acid, malic acid, acetic acid, citric acid, cinnamic acid, ρ-hydr oxybenzoic acid and benzoic acid of grafted seedlings were significantly higher than ungrafted seedlings as well.Therefore, more Cu2 + were restricted in soil by chelating, complexing and precipitation with root exudates, and its toxicity was decreased. The soil microbial biomass C and N in grafted cucumber rhizosphere were significantly higher than those in ungrafted cucumber rhizosphere, while basal respiration and metabolic quotient were significantly lower .Under Cu stress, the numbers of actinomyces and nitrogen fixing bacteria decreased and the number of fungi increased significantly, there there no significant difference in figures of bacteria. numbers of bacteria, actinomyces, and nitrogen fixing bacteria in grafted cucumber rhizosphere were significantly higher than those in ungrafted cucumber rhizosphere, but the number of fungi was opposite. these activities of soil urease, phosphatase, sucrase and catalase in grafted cucumber rhizosphere were significantly higher than those in ung rafted cucumber rhizosphere. [Conclusion] These indicated that the soil microbial environment and soil enzymes activities were improved by grafting under Cu stress, and as a result, the adaptability of cucumber to Cu stress was improved.