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 situ measurement 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 amoA abundance in the O and O+T plots. The nosZ abundance was significantly greater in the O+T plot, whilst the AOB amoA abundance 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.