Nitrite is a pivotal component of the marine nitrogen cycle. The fate of nitrite determines the loss or retention of fixed nitrogen, an essential nutrient for all organisms. Loss occurs via anaerobic nitrite reduction to gases during denitrification and anammox, while retention occurs via nitrite oxidation to nitrate. Nitrite oxidation is usually represented in biogeochemical models by one kinetic parameter and one oxygen threshold, below which nitrite oxidation is set to zero. Here we find that the responses of nitrite oxidation to nitrite and oxygen concentrations vary along a redox gradient in a Pacific Ocean oxygen minimum zone, indicating niche differentiation of nitrite-oxidizing assemblages. Notably, we observe the full inhibition of nitrite oxidation by oxygen addition and nitrite oxidation coupled with nitrogen loss in the absence of oxygen consumption in samples collected from anoxic waters. Nitrite-oxidizing bacteria, including novel clades with high relative abundance in anoxic depths, were also detected in the same samples. Mechanisms corresponding to niche differentiation of nitrite-oxidizing bacteria across the redox gradient are considered. Implementing these mechanisms in biogeochemical models has a significant effect on the estimated fixed nitrogen budget.

亚硝酸盐是海洋氮循环的关键组成部分。亚硝酸盐的命运决定了固定氮的损失或保留，固定氮是所有生物体的必需营养素。在反硝化和厌氧氨氧化过程中，通过厌氧亚硝酸盐还原为气体发生损失，而通过亚硝酸盐氧化为硝酸盐发生保留。亚硝酸盐氧化在生物地球化学模型中通常由一个动力学参数和一个氧阈值表示，低于该值亚硝酸盐氧化设为零。在这里，我们发现亚硝酸盐氧化对亚硝酸盐和氧气浓度的响应在太平洋氧气最小区域中沿着氧化还原梯度变化，表明亚硝酸盐氧化组合的生态位分化。尤其，我们观察到在从缺氧水域收集的样品中没有氧气消耗的情况下，通过添加氧气和亚硝酸盐氧化以及氮损失对亚硝酸盐氧化的完全抑制。在同一样本中还检测到亚硝酸盐氧化细菌，包括在缺氧深度具有高相对丰度的新型进化枝。考虑了与氧化还原梯度中亚硝酸盐氧化细菌的生态位分化相对应的机制。在生物地球化学模型中实施这些机制对估计的固定氮预算有重大影响。考虑了与氧化还原梯度中亚硝酸盐氧化细菌的生态位分化相对应的机制。在生物地球化学模型中实施这些机制对估计的固定氮预算有重大影响。考虑了与氧化还原梯度中亚硝酸盐氧化细菌的生态位分化相对应的机制。在生物地球化学模型中实施这些机制对估计的固定氮预算有重大影响。