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.