The discovery of comammox has altered our perception of the nitrogen biogeochemical cycle. However, their functional importance compared to canonical ammonia oxidisers (i.e., ammonia-oxidising bacteria (AOB) and archaea (AOA)) in agricultural soils remains elusive, especially in acidic soils. Here, we assessed the functional importance of these functional guilds in nitrification and nitrous oxide (NO) emissions in three acidic agricultural soils by using a range of nitrification inhibitors (acetylene, 3,4-dimethylpyrazole phosphate (DMPP) and different concentrations of 1-octyne) and monitored their community assemblage and population dynamics. The sensitivity of comammox clade A to 1-octyne varied across soils, highlighting that the inappropriate use of 1-octyne can lead to misestimation of comammox activity. AOA were key NH oxidisers in the three soils, while AOB also contributed significantly to nitrification in one soil. In contrast, comammox always played a minor role in ammonia oxidation and NO emissions, likely due to their low abundances, restricted cellular kinetic properties and NO production mechanisms. Together, this study demonstrates that comammox play a less important role in ammonia oxidation and NO production in acidic agricultural soils than AOA and AOB, thereby providing important novel insights into the mitigation of nitrogen fertiliser loss and NO emissions.

中文翻译：

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解读comammox与典型氨氧化剂在酸性农业土壤硝化和N2O排放中的功能重要性

comammox 的发现改变了我们对氮生物地球化学循环的看法。然而，与农业土壤中典型的氨氧化菌（即氨氧化细菌（AOB）和古细菌（AOA））相比，它们的功能重要性仍然难以捉摸，特别是在酸性土壤中。在这里，我们通过使用一系列硝化抑制剂（乙炔、3,4-二甲基吡唑磷酸盐（DMPP）和不同浓度的 1-辛炔）并监测其群落组合和种群动态。不同土壤中comammox clade A对1-辛炔的敏感性各不相同，这突出表明1-辛炔的不当使用可能导致comammox活性的错误估计。 AOA 是三种土壤中关键的 NH 氧化剂，而 AOB 对一种土壤中的硝化作用也有显着贡献。相比之下，comammox 在氨氧化和 NO 排放中始终发挥次要作用，这可能是由于其丰度较低、细胞动力学特性和 NO 产生机制受到限制。总之，这项研究表明，与 AOA 和 AOB 相比，comammox 在酸性农业土壤中的氨氧化和 NO 产生中发挥的作用不太重要，从而为减轻氮肥损失和 NO 排放提供了重要的新见解。