LAUSR

Nitrous oxide, one of the powerful long-lived greenhouse gases, is emitted mainly through biological processes, especially from fertilized soil. It is critical to partition the contribution of different pathways to N2O emissions and the relevant characteristics of microbial communities to identify the key N2O processes. An microcosm was conducted to partition the N2O emissions from different pathways, and the changes in soil mineral nitrogen and various nitrifiers (amoA bacteria and amoA archaea) and denitrifiers (nirS, nirK, and nosZ) were also determined using qPCR and high-throughput sequencing methods. Different gas inhibitor combinations (i.e., 0.06% acetylene, pure oxygen, 0.06% acetylene in pure oxygen, and pure helium) were used to partition the N2O pathways. A 5% oxygen treatment, with and without acetylene, was also included so that the N2O emissions could be measured under lower oxygen partial pressure. Results showed that ammonia-oxidation (AO) and successive nitrifier denitrification (NiD) were the main pathways contributing to N2O emissions at the earlier period after ammonium sulfate application with the cumulative N2O emissions accounting for 30.9% and 59.2% of the total N2O emissions, respectively. The higher NiD N2O contributions occurred when the soil nitrite concentration appeared higher, especially under the lower oxygen conditions. Higher N2O emissions from AO and NiD were associated with the compositional proportion of some dominant AOB species. Denitrification contributed more N2O (63.6%-69.3%) in the later period during incubation, coinciding with the following characteristics for denitrifiers: a) lower nosZ/(nirS + nirK) ratio, b) more diversity in nirS, and c) different proportions of some dominant species in nirK. Our results demonstrated that higher AO and successive NiD were the main N2O emission pathways, suggesting that controlling the ammonium content and weakening the AO are critical in decreasing N2O emissions.