nZVI decreases N2O emission from pesticide-contaminated paddy soil

The abundance and speciation of iron in farmland soils may affect the environmental fate of residual pesticides and their effects on soil N-cycling, which remains unclear. Herein, the roles of nanoscale zero-valent iron (nZVI) and iron oxidates (α-Fe2O3, γ-Fe2O3, and Fe3O4) as exogenous iron in reducing the adverse effect of pesticide pollution on soil N-cycling were firstly studied. It was found that the iron-based nanomaterials, especially nZVI, effectively reduced the N2O emission by 32.4-69.7 % at 5 g kg-1 from pentachlorophenol (PCP, as a representative pesticide, 100 mg kg-1) contaminated paddy soil, and remarkable N2O reduction (86.9 %) and PCP removal (60.9 %) were simultaneously achieved by applying 10 g kg-1 nZVI. Moreover, nZVI significantly mitigated the PCP-induced soil NO3--N accumulation and increased soil NH4+-N. Mechanistically, the nZVI restored the activities of nitrate- and N2O- reductases and the abundances of N2O-reducing microorganisms in the PCP-contaminated soil. Moreover, the nZVI suppressed N2O-producing fungi while promoting soil bacteria (especially nosZ-II bacteria) to increase N2O consumption in the soil. This study provides a strategy for adding iron-based nanomaterials to mitigate the adverse effects of pesticide residues on soil N-cycling and provides basic data for subsequent understanding of the effects of iron cycling in paddy soils on pesticide residues and N-cycling.