With the rapid development of nanotechnology,large amounts of metal nanoparticles(MNPs)will inevitably release to the environment,with soils predicted to be a substantial sink.As the most active and complex component in soil,microorganisms act closely to the migration and transformation of MNPs.In this study,two typical MNPs in different concentration gradients(TiO2 NPs-0,100,500,1000 mg/kg;CuO NPs-0,100,500,1000,20000 mg/kg)were applied to study the long-term effect and mechanism of MNPs to the microbes in paddy soil.Based on the results of DNA qualification,microbial biomass carbon and phospholipid fatty acid(PLFA),CuO NPs presented a significant inhibitory effect on soil microbial biomass while TiO2 NPs didnt.Phosphatase,urease and dehydrogenase were measured to represent soil microbial activity.TiO2 NPs rarely had significant responses to most enzymes,however,when the CuO NPs exceeded 500 mg/kg,all enzymes were strongly inhibited.The principle component analysis(PCA)of PLFA revealed that TiO2 NPs didnt alter the community structure of soil microbes under all the concentration treatments,when referred to CuO NPs,the alterations of lower concentrations(100,500 mg/kg)differed to the higher concentrations(1000,200 mg/kg).To seek the precise mechanism of different MNPs to soil microbes,we carry out one-step extraction,microbial available extraction and total content extraction of Cu in soil.It is obvious that TiO2 NPs didnt effect on any form of Cu content.Contrarily,the content of microbial available Cu raised rapidly with the CuO NPs increased which suggested that the massive available Cu was the major toxicity to microbes in paddy soil.Besides,the log Kp value of CuO NPs treatments was larger than 2.8 which mean that the CuO NPs had high solubility in all treated soils.In summary,TiO2 NPs might have lower ecobiological risks due to the less impact on soil microbes,while the environmental risks of CuO NPs needed to be urgently concerned because of their toxicity of released ions to soil microbes.