Elevated CO2 mitigates the negative effect of CeO2 and Cr2O3 nanoparticles on soil bacterial communities by alteration of microbial carbon use

The interactive effects of elevated atmospheric CO2 and nanoparticles (NPs) on the structure and function of soil bacterial community remain unknown. Here we compared the impacts of CeO2 (nCeO(2)) and Cr2O3 (nCr(2)O(3)) nanoparticles on the taxonomic compositions and functional attributes of bacterial communities under elevated CO2 (eCO(2)). The stimulated enzyme activities (dehydrogenase, acid phosphatase and urease), increased microbial biomass carbon (MBC), and higher bacterial alpha-diversity were observed under the combined effects of eCO(2) and NPs compared to the single NP treatment, indicating eCO(2) could mitigate the adverse effect of NPs on soil microorganisms. NPs and eCO(2) are important factors influencing the alpha- and beta-diversity (17% and 18% of variations were explained) as well as functional profile (20% and 26% of variations were explained) of bacterial communities. Rising CO2 level promoted the resilience of NP-resistant bacterial populations, primarily the members of Alphaproteobacteria, Gammaproteobacteria and Bacteroidia, which are also characterized by the fast carbon use capability. Moreover, the significantly (P < 0.05) higher metabolic quotient (qCO(2)), reduced available carbon and overrepresented carbon metabolism genes at eCO(2) vs. ambient CO2 (aCO(2)) indicate the acceleration of available carbon turnover in NP-exposed soils. Correlation analysis revealed that mitigation of NPs toxicity by eCO(2) could be attributed to the remarkable decline of bioavailable metals disassociated from NPs and available carbon level, as well as promotion of the rapid carbon-metabolizing microbes. Our study pointed out the positive role of eCO(2) in alleviating the adverse effect of NPs on microbiological soil environment, and results can serve as important basis in establishing guidelines for lowering the eco-toxicity of NPs. (C) 2020 Elsevier Ltd. All rights reserved.