Collaborative Research: Nitrous oxide reduction in oxygen minimum zones: an understudied but critical loss term in ocean greenhouse gas cycling

一氧化二氮(N2O)是一种由水生和陆地环境中的微生物产生的气体，与其他温室气体一样，它导致了全球变暖。此外，N2O可以破坏臭氧，臭氧是一种负责保护地球免受危险紫外线辐射的气体。在海洋中，N2O的产生在很大程度上受可用溶解氧量的控制，在低氧浓度下产生更多的N2O；然而，当没有氧气可用时，海洋中的微生物从产生N2O转变为消耗N2O。近年来，在海洋的一些区域，低氧区正在扩大，这引起了人们对将产生更多N2O的担忧。如果发生这种情况，更多的N2O将被排放到大气中，并将导致进一步的全球变暖和臭氧破坏。正因为如此，研究主要集中在了解海洋在低氧条件下产生多少N2O。然而，如果缺氧区的大小也增加了，这至少在一定程度上可以抵消因氧气存在但浓度较低的区域的扩大而导致的N2O产量的预期增加。这项研究的目的是同时测量低氧和缺氧区的N2O产生和消耗，并确定负责N2O产生和消耗的微生物。我们的结果将：1)更好地理解如果海洋低氧区继续扩大，缺氧区的N2O消耗如何有助于平衡N2O产量的增加；2)有助于为旨在预测未来海洋条件下海洋N2O产量和向大气排放的模型提供信息；3)使我们能够更好地了解参与N2O生产和消费的微生物。我们的研究将支持一名博士后和本科生，他们将从事海洋化学和群落基因组学的研究。私人投资机构计划具体考虑来自代表性不足的少数族裔和机会有限的机构的学生的申请。私人投资机构还计划开展其他一些教育/外展项目，包括教师培训讲习班、教师实习以及学术和公共系列讲座。海洋中温室气体和臭氧破坏气体一氧化二氮(N2O)的产量随着溶解氧(DO)浓度从有氧向低氧的转变而增加。随着气候变化，全球海洋DO浓度下降，海洋缺氧区扩大，并预计将继续扩大。这一增长引起了人们的担忧，即未来海洋中N2O的产量将增加，这将导致向大气排放更高的N2O。因此，许多研究都集中在量化与N2O产量大幅增加对应的氧气阈值上。相比之下，相对较少的研究旨在量化在缺氧条件下微生物将N2O还原为氮气所产生的N2O净消费能力，以缓冲如果缺氧区与缺氧区一起扩大时N2O产量的预测增加。为此，这项研究旨在同时量化氧化-缺氧-缺氧水柱区域的N2O产量和消费量，以确定N2O消费量抵消N2O产量预期增长的潜力。我们的野外工作将在不列颠哥伦比亚湾的萨尼奇湾进行，这是我们研究的理想天然实验室，因为它的特点是建立了完善的氧跃层和缺氧区。具体地说，我们的目标是1)测量总体N2O浓度，并使用15N示踪技术，量化N2O的产生和消耗速率，以及浓度从缺氧到缺氧条件下的浓度下降；2)量化缺氧区的N2O消耗与上覆低氧区域增加的N2O产生的幅度；以及3)明确地将观察到的N2O产生和消耗速率与参与这一过程的微生物联系起来，特别关注区分通过反硝化菌(N3-到N2)和非反硝化菌(N2O到N2)的N2O消耗。最终，我们的结果将提供关于波动海洋条件下N2O消耗率的定量信息，从而有助于限制氧气对N2O净产生和海洋-大气温室气体通量的影响模型。此外，这项工作将确定能够还原N2O的微生物的分类广度及其与实际N2O减少率的联系，从而提供对特定生物特征的检测是否可以预测海洋N2O动态的定量了解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nitrous oxide (N2O) is a gas produced by microbes in both aquatic and terrestrial environments, and, like other greenhouse gases, it contributes to global warming. Furthermore, N2O can destroy ozone, a gas responsible for protecting the earth from dangerous ultraviolet radiation. In the ocean, N2O production is largely controlled by the amount of available dissolved oxygen, with more N2O being produced under low oxygen concentrations; however, when no oxygen is available, a scenario referred to as anoxia, microbes in the ocean switch from producing N2O to consuming N2O. In recent years, it has become evident that zones of low oxygen are expanding in some areas of the oceans, and this has raised concern that more N2O will be produced. If this occurs, more N2O will be emitted to the atmosphere, and will lead to further global warming and ozone destruction. Because of this, research has largely focused on understanding how much N2O is produced in the ocean under low oxygen conditions. If, however, anoxic zones also increase in size, this could act to balance out, at least to some degree, the predicted increase in N2O production caused by the expansion of zones where oxygen is present but in low concentrations. This study aims to simultaneously measure N2O production and consumption, in both low oxygen and anoxic zones and identify the microbes responsible for N2O production and consumption. Our results will: 1) lead to a much better understanding of how N2O consumption in anoxic zones could help to balance out an increase in N2O production if low oxygen zones in the ocean continue to expand, 2) help to inform models aimed at predicting oceanic N2O production and emissions to the atmosphere under future ocean conditions, and 3) allow us to better understand the microbes involved in N2O production and consumption. Our study will support a postdoc and undergraduate students who will work at the interface of marine chemistry and community genomics. The PIs plan to specifically consider applications from underrepresented minorities and students at institutions with limited opportunities. The PIs also plan a number of other educational/outreach programs ranging from teacher-training workshops, teacher internships, and academic and public lecture series. The oceanic production of the potent greenhouse and ozone destroying gas nitrous oxide (N2O) increases as dissolved oxygen (DO) concentrations transition from oxic to hypoxic. Marine DO concentrations have decreased globally with climate change and oceanic hypoxic zones have expanded and predicted to continue expanding. This increase is cause for concern that N2O production in the ocean will increase in the future which would lead to higher emissions to the atmosphere. As a result, much research has focused on quantifying the oxygen thresholds that correspond to large increases in N2O production. In contrast, relatively few studies have aimed to quantify the capacity for net N2O consumption, resulting from microbial N2O reduction to N2 under anoxic conditions, to buffer against predicted N2O production increases if anoxic zones expand in conjunction with hypoxic zones. To this end, this study aims to simultaneously quantify N2O production and consumption from oxic-hypoxic-anoxic water column zones, in order to determine the potential for N2O consumption to counteract predicted increases in N2O production. Our field work be conducted in Saanich Inlet, a British Columbian fjord which is an ideal natural laboratory for our study, as it is characterized by a well-established oxycline and anoxic zone. Specifically, we aim to 1) measure bulk N2O concentrations, and, using 15N tracer techniques, quantify N2O production and consumption rates as DO concentrations decrease from oxic to anoxic conditions, 2) quantify the magnitude by which N2O consumption in the anoxic zone balances increased N2O production in the overlying hypoxic region, and 3) definitively link observed N2O production and consumption rates to the microorganisms mediating this process, focusing specifically on distinguishing N2O consumption via denitrifier (NO3- to N2) versus non-denitrifier (N2O to N2 only) taxa. Ultimately, our results will provide quantitative information on N2O consumption rates over fluctuating ocean conditions, thereby helping constrain models of oxygen effects on net N2O production and ocean-to-atmosphere greenhouse gas fluxes. Furthermore, this work will identify the taxonomic breadth of microbes capable of N2O reduction and their linkage to actual N2O reduction rates, thereby providing a quantitative understanding of whether or not the detection of specific bio-signatures is predictive of marine N2O dynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.