Department of Geosciences, Princeton University, Princeton, NJ, 08544, USA.
Department of Environmental Science, University of Basel, Basel, Switzerland.
ISME J. 2021 May;15(5):1317-1329. doi: 10.1038/s41396-020-00852-3. Epub 2021 Jan 6.
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，而固定氮是所有生物的必需营养物质。损失是通过反硝化和厌氧氨氧化过程中亚硝酸盐的厌氧还原为气体而发生的，而保留是通过亚硝酸盐氧化为硝酸盐而发生的。在生物地球化学模型中，亚硝酸盐氧化通常由一个动力学参数和一个氧气阈值来表示，低于该阈值，亚硝酸盐氧化被设定为零。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沿着太平洋缺氧区的氧化还原梯度而变化，表明了亚硝酸盐氧化菌群的生态位分化。值得注意的是，我们观察到在缺氧水样中，即使没有氧气消耗，添加氧气也会完全抑制亚硝酸盐氧化，并且在没有氧气消耗的情况下，亚硝酸盐氧化伴随着氮的损失。在同一水样中还检测到了包括在缺氧深度具有高相对丰度的新型进化枝在内的亚硝酸盐氧化细菌。考虑了亚硝酸盐氧化细菌在氧化还原梯度上的生态位分化的机制。在生物地球化学模型中实施这些机制对估计固定氮预算有显著影响。
