Decreased nitrous oxide emissions associated with functional microbial genes under bio-organic fertilizer application in vegetable fields

Bio-organic fertilizers enriched with plant growth-promoting microbes (PGPMs) have been widely used in crop fields to promote plant growth and maintain soil microbiome functions. However, their potential effects on N2O emissions are of increasing concern. In this study, an in situmeasurement experiment was conducted to investigate the effect of organic fertilizer containing Trichoderma guizhouense(a plant growth-promoting fungus) on soil N2O emissions from a greenhouse vegetable field. The following four treatments were used: no fertilizer (control), chemical fertilizer (NPK), organic fertilizer derived from cattle manure (O), and organic fertilizer containing T guizhouense(O+T, referring to bio-organic fertilizer). The abundances of soil N cycling-related functional genes (amoA) from ammonium-oxidizing bacteria (AOB) and archaea (AOA), as well as nirS, nirK,and nosZ,were simultaneously determined using quantitative PCR (qPCR). Compared to the NPK plot, seasonal total N2O emissions decreased by 11.7% and 18.7% in the O and O+T plots, respectively, which was attributed to lower NH4+-N content and AOB amoAabundance in the O and O+T plots. The nosZabundance was significantly greater in the O+T plot, whilst the AOB amoAabundance was significantly lower in the O+T plot than in the O plot. Relative to the organic fertilizer, bio-organic fertilizer application tended to decrease N2O emissions by 7.9% and enhanced vegetable yield, resulting in a significant decrease in yield-scaled N2O emissions. Overall, the results of this study suggested that, compared to organic and chemical fertilizers, bio-organic fertilizers containing PGPMs could benefit crop yield and mitigate N2O emissions in vegetable fields.