Effects of Metal Oxide Nanoparticles on Nitrous Oxide Emissions in Agriculture Soil

Metal oxide nanoparticles (NPs) have been widely used in industrial and agricultural production and introduced into soils. The impact of these nanoparticles on soil nitrous oxide (N2O) emission is unclear. We conducted a microcosm experiment to investigate the effects of titanium oxide nanoparticles (TiO2 NPs), copper oxide nanoparticles (CuO NPs), and aluminum oxide nanoparticles (Al2O3 NPs) on soil N2O emissions and the abundance of functional genes related to N2O production/reduction. Compared to the soil without NPs addition, TiO2 NPs applied to the soil produced no significant effect on N2O emissions. The denitrification process in the soil exposed to CuO NPs was inhibited by reducing the functional genes related to nitrite reductase (nirK) and increasing N2O reductase (nosZ), while CuO NPs added to the soil stimulated the cumulative N2O emissions by 92.7%. After the application of Al2O3 NPs to the soil, the nitrification process was inhibited by inhibiting the functional genes of ammonia-oxidizing bacteria (AOB amoA), and soil N2O emission was reduced by 48.6%. Large-scale application of CuO NPs in agricultural soils may stimulate the N2O emissions resulting in potential environmental risks.