Enhanced N2O emission rate in field soil undergoing conventional intensive fertilization is attributed to the shifts of denitrifying guilds

ABSTRACT The emission of greenhouse gas N2O in agricultural soil is modulated by N fertilization that could be converted to N2O by denitrifiers under anaerobic condition. Nevertheless, the effect of denitrifiers on N2O emission has not been thoroughly elucidated. In this study, we explored the denitrifying gas kinetics, nitrate content, transcribed denitrifying functional genes (narG, nirS, nirK, and nosZ), and the active bacteria during anaerobic incubation of soils with conventional intensive N fertilization (CNS) and reduced N fertilization (RNS), both sampled from a vegetable greenhouse experimental site. The CNS sample showed significantly higher N2O emission rates relative to the RNS sample. However, the difference in N2O emission between the soils was neither because of the cumulative nitrate content nor the quantity of denitrifying gene transcripts. The distinct fertilization regimes shaped the significantly different bacterial communities in these soils. The absolute abundance of bacteria that produce N2O but lack the nosZ gene for N2O reduction (for example, the dominant Kaistobacter) was higher in CNS than in RNS. Meanwhile, the abundance of two operational taxonomy units (OTUs), namely Rhodanobacter, belonging to the most abundant genus in denitrifying guilds, was strongly enriched in CNS and showed significant positive correlation with N2O/(N2O + N2). The predominance of these bacterial OTUs in the CNS denitrifying guild strongly suggested that high N2O emission from the soil with long-term conventional intensive fertilization might be primarily attributed to the reshaping of distinct denitrifying guilds in their bacterial communities.