Copper oxide nanoparticles inhibited denitrifying enzymes and electron transport system activities to influence soil denitrification and N2O emission

Nanopesticides are widely applied in modern agricultural systems to replace traditional pesticides, which inevitably leads to their accumulation in soils. Nanopesticides based on copper oxide nanoparticles (CuO NPs) may affect the soil nitrogen cycle, such as the denitrification process; however, the mechanism remains unclear. Here, acute exposure experiments for 60 h were conducted to explore the effects of CuO NPs (10, 100, 500 mg kg−1) on denitrification. In this study, Cu speciation, activities of denitrifying enzymes, electron transport system activity (ETSA), expression of denitrifying functional genes, composition of bacterial communities and reactive oxygen species (ROS) were determined. In all treatments, Cu ions was the dominant form and responsible for the toxicity of CuO NPs. The results indicated that CuO NPs treatments at 500 mg kg−1 remarkably inhibited denitrification, led to an 11-fold increase in NO3− accumulation and N2O emission rates decrease by 10.2–24.1%. In the denitrification process, the activities of nitrate reductase and nitric oxide reductase reduced by 21.1–42.1% and 10.3–16.3%, respectively, which may be a reason for the negative effect of CuO NPs. In addition, ETSA was significantly inhibited with CuO NPs applications, which reflects the ability of denitrification to accept electrons. Denitrifying functional genes and bacterial communities composition were changed, thus further influencing the denitrification process. ROS analysis showed that there were no significant differences among NPs treatments. This research improves the understanding of CuO NPs impact on soil denitrification. Further attention should be paid to the nitrogen transformation in agricultural soils in the presence of nanopesticides.