Distinctive effects of TiO2 and CuO nanoparticles on soil microbes and their community structures in flooded paddy soil

•TiO2 NPs and CuO NPs perturb soil microbial biomass and activity distinctively.•CuO NPs reduce the composition and diversity of the soil microbial community.•The microbial impact of TiO2 NPs is induced by their particle properties.•The high bioavailability of CuO NPs is the main source of microbial toxicity.•Both TiO2 NPs and CuO NPs showed potential risks to the paddy soil ecosystem.

The wide use of metal oxide nanoparticles (MNPs) will inevitably increase their environmental release into soil, which consequently raises concerns about their environmental impacts and ecological risks. In this study, two typical MNPs (TiO2 and CuO NPs) in different doses (0, 100, 500 and 1000 mg kg−1 soil) were applied to evaluate their effects on microbes in flooded paddy soil. The negative effects of CuO NPs were stronger than that of TiO2 NPs on soil microbes, as reflected by the significant decline in soil microbial biomass (as indicated by the reduced microbial biomass carbon [MBC] and the total phospholipid fatty acids [PLFAs]) and enzyme activities including urease, phosphatase and dehydrogenase. The principle component analysis (PCA) of the PLFAs and the diversity indices reveal that not TiO2 NPs but CuO NPs reduced the composition and diversity of the paddy soil microbial community. The reduced impact of TiO2 NPs may be due to their particle characteristics. The bioavailability of CuO NPs is thought to induce the major toxicity to microbes in the flooded paddy soil, as determined by the increased Cu contents in the soil extractions and the microbial cells. The elevated stress ratio values demonstrate that CuO NPs may also indirectly affect soil microbes by changing nutrient bioavailability. Over all, both TiO2 NPs and CuO NPs may induce perturbations on the microbes in flooded paddy soil and showed potential risks to the paddy soil ecosystem. Therefore, attentions toward the effects of MNPs to the ecological environment should be paid from now on.

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