Nitrogen addition to croplands greatly increases global emissions of the potent greenhouse gas nitrous oxide (N₂O). Three ammonia-oxidizing functional guilds constitute the major producers of N₂O in agricultural soils, but their relative contributions are still poorly understood, especially the newly discovered and widespread complete ammonia oxidizers (comammox). To fill this knowledge gap, we used three nitrification inhibitors: acetylene, 1-octyne, and 3,4-dimethylpyrazole phosphate (DMPP), to selectively suppress the activity of different ammonia oxidizer guilds to discriminate their relative contributions to N₂O production in an alkaline arable soil. The results indicated that DMPP completely inhibited the growth of comammox Nitrospira clade A and ammonia-oxidizing bacteria (AOB) but promoted ammonia-oxidizing archaea (AOA) growth, while the abundance of comammox Nitrospira clade A increased in the presence of 1-octyne at high ammonium (NH₄⁺) concentrations. AOB dominated N₂O production in soils with inorganic NH₄⁺ amendment, followed by AOA, while comammox Nitrospira contributed to less than 3% of total N₂O emissions with an N₂O yield of ∼0.083% (N₂O per molecule of nitrate). The abundance of comammox Nitrospira clade A was approximately two orders of magnitude lower than that of canonical ammonia-oxidizers. Phylogenetic analysis revealed that the majority of comammox Nitrospira clade A belonged to a new cluster that was separated from the known comammox bacterium. Taken together, our results clearly and strongly demonstrate that comammox Nitrospira play only a minor role in N₂O emissions in a heavily fertilized alkaline arable soil.

向农田添加氮会大大增加强效温室气体一氧化二氮 (N ₂ O) 的全球排放量。三个氨氧化功能团构成了农业土壤中 N ₂ O 的主要生产者，但它们的相对贡献仍然知之甚少，尤其是新发现和广泛存在的完全氨氧化剂 (comammox)。为了填补这一知识空白，我们使用了三种硝化抑制剂：乙炔、1-辛炔和 3,4-二甲基吡唑磷酸盐 (DMPP)，以选择性地抑制不同氨氧化剂协会的活性，以区分它们对 N ₂ O 产生的相对贡献。一种碱性耕地。结果表明，DMPP完全抑制了comammox Nitrospira的生长。进化枝 A 和氨氧化细菌 (AOB) 但促进氨氧化古细菌 (AOA) 的生长，而在高铵 (NH ₄ ⁺ ) 浓度下存在 1-辛炔的情况下，comammox Nitrospira clade A 的丰度增加。在使用无机 NH ₄ ⁺改良剂的土壤中， AOB 主导 N ₂ O 的产生，其次是 AOA，而 comammox Nitrospira对 N ₂ O 总排放量的贡献不到 3%， N ₂ O 产量约为 0.083%（每分子N ₂ O硝酸盐）。comammox Nitrospira的丰度进化枝 A 比典型的氨氧化剂低大约两个数量级。系统发育分析表明，大多数 comammox Nitrospira clade A 属于一个新的簇，该簇与已知的 comammox 细菌分离。总之，我们的结果清楚而有力地表明，comammox Nitrospira在大量施肥的碱性耕地土壤中的 N ₂ O 排放中仅起次要作用。