Effect of Zinc Oxide Nanoparticles on Nitrous Oxide Emissions in Agricultural Soil

Zinc oxide nanoparticles (ZnO NPs) are widely used and exposed to the soil environment, but their effect on soil nitrous oxide (N2O) emissions remains unclear. In this study, a microcosm experiment was conducted to explore the effects of different ZnO NPs concentrations (0, 100, 500, and 1000 mg kg−1) on N2O emissions and associated functional genes related to N2O amendment with carbon (C) or nitrogen (N) substrates. Partial least squares path modeling (PLS-PM) was used to explore possible pathways controlling N2O emissions induced by ZnO NPs. In the treatment without C or N substrates, 100 and 500 mg kg−1ZnO NPs did not affect N2O production, but 1000 mg kg−1ZnO NPs stimulated N2O production. Interestingly, compared with the soils without ZnO NPs, the total N2O emissions in the presence of different ZnO NPs concentrations increased by 2.36–4.85-, 1.51–1.62-, and 6.28–8.35-fold following C, N and both C & N substrate amendments, respectively. Moreover, ZnO NPs increased the functional genes of ammonia-oxidizing bacteria (AOBamoA) and nitrite reductase (nirS) and led to the exhaustion of nitrate but reduced the gene copies of ammonia-oxidizing archaea (AOAamoA). In addition, the redundancy analysis results showed that the AOBamoAandnirSgenes were positively correlated with total N2O emissions, and the PLS-PM results showed that ZnO NPs indirectly affected N2O emissions by influencing soil nitrate content, nitrifiers and denitrifiers. Overall, our results showed that ZnO NPs increase N2O emissions by increasing nitrification (AOBamoA) and denitrification (nirS), and we highlight that the exposure of ZnO NPs in agricultural fields probably results in a high risk of N2O emissions when coupled with C and N substrate amendments, contributing to global climate warming.Keywords:nanomaterials;nitrification;denitrification;nitrous oxide;soil