Denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) are three competing processes of microbial nitrate reduction that determine the degree of ecosystem nitrogen (N) loss versus recycling. However, the global patterns and drivers of relative contributions of these N cycling processes to soil or sediment nitrate reduction remain unknown, limiting our understanding of the global N balance and management. Here, we compiled a global dataset of 1570 observations from a wide range of terrestrial and aquatic ecosystems. We found that denitrification contributed up to 66.1% of total nitrate reduction globally, being significantly greater in estuarine and coastal ecosystems. Anammox and DNRA could account for 12.7% and 21.2% of total nitrate reduction, respectively. The contribution of denitrification to nitrate reduction increased with longitude, while the contribution of anammox and DNRA decreased. The local environmental factors controlling the relative contributions of the three N cycling processes to nitrate reduction included the concentrations of soil organic carbon, ammonium, nitrate, and ferrous iron. Our results underline the dominant role of denitrification over anammox and DNRA in ecosystem nitrate transformation, which is crucial to improving the current global soil N cycle model and achieving sustainable N management.

中文翻译：

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反硝化作用主导全球自然生态系统的异化硝酸盐还原

反硝化、厌氧氨氧化 (anammox) 和异化硝酸盐还原为铵 (DNRA) 是微生物硝酸盐还原的三个相互竞争的过程，决定了生态系统氮 (N) 损失与回收的程度。然而，这些氮循环过程对土壤或沉积物硝酸盐减少的相对贡献的全球模式和驱动因素仍然未知，限制了我们对全球氮平衡和管理的理解。在这里，我们编译了来自广泛的陆地和水生生态系统的 1570 个观测数据的全球数据集。我们发现反硝化作用占全球硝酸盐总减少量的 66.1%，在河口和沿海生态系统中这一比例要高得多。 Anammox 和 DNRA 分别可减少硝酸盐总量的 12.7% 和 21.2%。反硝化作用对硝酸盐还原的贡献随着经度的增加而增加，而厌氧氨氧化和DNRA的贡献则减少。控制三个氮循环过程对硝酸盐还原的相对贡献的当地环境因素包括土壤有机碳、铵、硝酸盐和二价铁的浓度。我们的研究结果强调了反硝化在生态系统硝酸盐转化中相对于厌氧氨氧化和DNRA的主导作用，这对于改善当前全球土壤氮循环模型和实现可持续氮管理至关重要。