Microbially mediated mechanisms underlie the increased soil N2O emissions under nitrogen fertilization in purple soil

Soil nitrous oxide (N₂O) originates from multiple processes, and nitrogen (N) fertilizer often increases N₂O emissions. However, the dominant processes, the contributions of major microbial taxa, and the potential mechanisms of N₂O production in purple soil with long-term N application are unclear. We conducted a 2-year field fertilization experiment, utilizing metagenomic techniques and selective inhibition tests, to investigate the potential mechanisms of N₂O emissions under 0, 180, and 360 kg N ha⁻¹ yr⁻¹ fertilization levels. In this study, N fertilizer increased soil N₂O emissions and emission factor (EF), with the range of cumulative N₂O emissions and EF being 0.13–3.47 kg N₂O-N ha⁻¹ yr⁻¹ and 0.47–0.91 %, respectively. Meanwhile, indoor culture tests revealed that N fertilizer mainly promoted N₂O production driven by ammonia-oxidizing bacteria (AOB) and the denitrification process, but decreased N₂O production driven by ammonia-oxidizing archaea (AOA) and complete ammonia oxidizers (comammox). By influencing soil NH₄⁺-N, NO₂⁻-N, AOB, Nitrosospira, and nosZ abundance, long-term N application indirectly impacted N₂O emissions. In addition, the accumulated NO₂⁻-N concentration and the increased AOB, nirK, norB, and Nitrosospira abundance following N application suggested that nitrifier denitrification (ND) may also contribute to the formation of N₂O. These findings suggest that AOB-driven nitrification and/or ND may be the main mechanisms for the increased N₂O emissions after N application in purple soil.