Department of Geosciences, Princeton University, Princeton, NJ, 08544, USA.
Department of Earth System Science, Stanford University, Stanford, CA, 94305, USA.
ISME J. 2021 May;15(5):1434-1444. doi: 10.1038/s41396-020-00861-2. Epub 2020 Dec 21.
The ocean is a net source of NO, a potent greenhouse gas and ozone-depleting agent. However, the removal of NO via microbial NO consumption is poorly constrained and rate measurements have been restricted to anoxic waters. Here we expand NO consumption measurements from anoxic zones to the sharp oxygen gradient above them, and experimentally determine kinetic parameters in both oxic and anoxic seawater for the first time. We find that the substrate affinity, O tolerance, and community composition of NO-consuming microbes in oxic waters differ from those in the underlying anoxic layers. Kinetic parameters determined here are used to model in situ NO production and consumption rates. Estimated in situ rates differ from measured rates, confirming the necessity to consider kinetics when predicting NO cycling. Microbes from the oxic layer consume NO under anoxic conditions at a much faster rate than microbes from anoxic zones. These experimental results are in keeping with model results which indicate that NO consumption likely takes place above the oxygen deficient zone (ODZ). Thus, the dynamic layer with steep O and NO gradients right above the ODZ is a previously ignored potential gatekeeper of NO and should be accounted for in the marine NO budget.
海洋是一氧化二氮（一种强效温室气体和消耗臭氧物质）的净源。然而，微生物通过消耗一氧化二氮去除一氧化二氮的作用受到很大限制，并且速率测量一直局限于缺氧水域。在这里，我们将缺氧区的一氧化二氮消耗测量扩展到它们上方的氧气梯度，并首次在有氧和缺氧海水中实验确定动力学参数。我们发现，好氧水中消耗一氧化二氮的微生物的基质亲和力、氧气耐受性和群落组成与底层缺氧层中的微生物不同。这里确定的动力学参数用于模拟原位一氧化二氮的产生和消耗速率。估计的原位速率与测量的速率不同，这证实了在预测一氧化二氮循环时必须考虑动力学。好氧层中的微生物在缺氧条件下以比缺氧区中的微生物快得多的速度消耗一氧化二氮。这些实验结果与模型结果一致，表明一氧化二氮消耗可能发生在缺氧区上方。因此，在缺氧区上方存在氧气和一氧化二氮梯度陡变的动态层是一氧化二氮的一个以前被忽视的潜在守门员，应该在海洋一氧化二氮预算中加以考虑。
