Abstract: A pot experiment with cucumber (taking Cucurbita ficifolia B. as the rootstock) was conducted to study the effects of grafting on the microbial population, microbial biomass, and enzyme activities in rhizospheric soil under copper stress. Under the stress of copper, the microbial biomass C and N in grafted and self-rooted cucumber rhizospheric soils all decreased significantly, while the basal respiration and metabolic quotient were in adverse. In grafted cucumber rhizospheric soil, the microbial biomass C and N were significantly higher than those in self-rooted cucumber rhizospheric soil, whereas the basal respiration and metabolic quotient were significantly lower. Under copper stress, the quantities of actinomyces and nitrogen-fixing bacteria in rhizospheric soils decreased and that of fungi increased significantly, whereas the quantity of bacteria had less change. In grafted cucumber rhizospheric soil, the quantities of bacteria, actinomyces, and nitrogen-fixing bacteria were significantly higher than those in self-rooted cucumber rhizospheric soil, but the quantity of fungi was in opposite. The urease, phosphatase, sucrase, and catalase activities were significantly higher in grafted than in self-rooted cucumber rhizospheric soil. All the results suggested that grafting could mitigate the impact of copper stress on the microbial micro-environment and enzyme activities in cucumber rhizospheric soil, and as a result, improve the adaptability of cucumber to copper stress.

Key words: grafting, copper stress, rhizosphere, soil microorganism, soil enzyme, PM_2.5, meteorological factors, forest stand.