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

合作研究：最低氧气区的一氧化二氮还原：海洋温室气体循环中一个尚未充分研究但至关重要的损失项

• 批准号: 2341290
• 负责人: Damian Grundle
• 金额: $ 54.58万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-10-01 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2341290&HistoricalAwards=false
• 关键词: Collaborative; Research; Nitrous; oxide; reduction

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.

一氧化二氮 (N2O) 是水生和陆地环境中微生物产生的一种气体，与其他温室气体一样，它会导致全球变暖。此外，N2O 会破坏臭氧，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 的产生很大程度上取决于可用溶解氧的量，低氧浓度下会产生更多的 N2O；然而，当没有氧气时（称为缺氧），海洋中的微生物就会从产生 N2O 转变为消耗 N2O。近年来，一些海洋区域的低氧区域正在扩大，这已经引起了人们对将产生更多氧化亚氮的担忧。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层破坏。因此，研究主要集中在了解低氧条件下海洋中产生了多少 N2O。然而，如果缺氧区域的面积也增加，这可能至少在某种程度上抵消由于存在氧气但浓度较低的区域扩大而导致的预计 N2O 产量增加。本研究旨在同时测量低氧和缺氧区域的 N2O 产生和消耗，并确定导致 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中的低氧区域继续扩大，缺氧区域的 N2O 消耗如何有助于平衡 N2O 产量的增加，2）有助于为旨在预测海洋的模型提供信息未来海洋条件下 N2O 的产生和向大气的排放，3）使我们能够更好地了解参与 N2O 产生和消耗的微生物。我们的研究将为博士后和本科生提供支持，他们将在海洋化学和社区基因组学的交叉领域工作。 PI 计划特别考虑代表性不足的少数族裔和机会有限的院校学生的申请。 PI 还计划了许多其他教育/推广计划，包括教师培训研讨会、教师实习以及学术和公共讲座系列。随着溶解氧 (DO) 浓度从含氧到缺氧的转变，海洋中产生的强效温室气体和臭氧破坏气体一氧化二氮 (N2O) 也会增加。随着气候变化，全球海洋溶解氧浓度下降，海洋缺氧区扩大并预计将继续扩大。这种增加令人担心未来海洋中氧化亚氮的产生量将会增加，从而导致向大气中的排放量增加。因此，许多研究都集中在量化与 N2O 产量大幅增加相对应的氧阈值。相比之下，相对较少的研究旨在量化缺氧条件下微生物 N2O 还原为 N2 所产生的净 N2O 消耗能力，以缓冲缺氧区域与缺氧区域一起扩大时预计的 N2O 产量增加。为此，本研究旨在同时量化含氧-缺氧-缺氧水体区域的 N2O 产量和消耗量，以确定 N2O 消耗量抵消 N2O 产量预计增加的潜力。我们的实地工作在不列颠哥伦比亚省的萨尼奇湾进行，这里是我们研究的理想天然实验室，因为它的特点是完善的氧斜层和缺氧区。具体来说，我们的目标是 1) 测量大量 N2O 浓度，并使用 15N 示踪技术，量化当 DO 浓度从好氧条件降低到缺氧条件时 N2O 的产生和消耗率，2) 量化缺氧区平衡中 N2O 消耗增加的幅度上层缺氧区域的 N2O 产生，以及 3）明确地将观察到的 N2O 产生和消耗率与介导该过程的微生物联系起来，特别注重区分通过反硝化菌（NO3-到 N2）与非反硝化菌（仅从 N2O 到 N2）分类群的 N2O 消耗。最终，我们的结果将提供波动海洋条件下 N2O 消耗率的定量信息，从而帮助约束氧气对 N2O 净产量和海洋到大气温室气体通量的影响模型。此外，这项工作将确定能够减少 N2O 的微生物的分类广度及其与实际 N2O 减少率的联系，从而定量了解特定生物特征的检测是否可以预测海洋 N2O 动态。该奖项反映了通过使用基金会的智力价值和更广泛的影响审查标准进行评估，NSF 的法定使命被认为值得支持。