Nitrous Oxide Consumption in Surface Waters

地表水中一氧化二氮的消耗量

• 批准号: 2342493
• 负责人: Bess Ward
• 金额: $ 58.2万
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-09-01 至 2027-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2342493&HistoricalAwards=false
• 关键词: Nitrous; Oxide; Consumption; Surface; Waters

Nitrous oxide (N2O) is a trace component of Earth’s atmosphere. It is a strong greenhouse gas, whose concentration has been increasing since the industrial revolution, and contributes about 6% to the total greenhouse effect. N2O is also implicated in ozone depletion in the stratosphere. The ocean is a net source of N2O to the atmosphere. N2O is produced and consumed in the ocean by microbes as part of the nitrogen cycle. The conversion of N2O to N2 (dinitrogen gas) is the only known biological sink for N2O and is catalyzed by an enzyme that is strongly inhibited by oxygen, so N2O consumption has been thought to be confined to oxygen-free environments. Thus, it was surprising to find that the genetic capability for N2O consumption was both present and active in the surface ocean, where oxygen is abundant. Experiments showed that surface ocean microbes rapidly consume N2O when oxygen is removed. It appears that the microbes can use N2O as an alternative to oxygen for respiration. Why would it be advantageous to retain this capacity in fully oxygenated surface water? Does this potential N2O consumption constitute an actual sink for N2O, which might reduce the net transfer of N2O from the ocean to the atmosphere? The reduction of nitrous oxide (N2O) to N2 is considered to be an obligately anaerobic process, usually restricted to anoxic environments in water and sediments. Previous work showed that the genes (nosZ) encoding the N2O reductase enzyme were both present and expressed in the surface ocean, and that surface ocean samples rapidly reduce N2O to N2 when oxygen is removed. The nosZ genes in surface waters appear to belong almost exclusively to microbes that do not perform the upstream steps in denitrification – they are facultative N2O respirers. The research proposed here will investigate the factors that might control or stimulate N2O reduction in surface waters and characterize the microbes responsible for the process. Experiments will test the hypothesis that N2O respirers are versatile heterotrophs whose activity is related to organic matter supply and possibly associated with particulate material or linked to in situ primary production. Researchers will perform 15N tracer incubations to measure the rate of N2O reduction and its response to various kinds of organic substrates, including in situ particulate material and fresh phytoplankton exudates. The quantity and community composition of nosZ-containing microbes will be determined using a suite of molecular biological methods – necessary because the nosZ gene is so diverse that previous methods have likely underestimated both its abundance and diversity and may not have identified the main microbes responsible for the process. Draft genomes of nosZ-containing microbes will be characterized to investigate their carbon metabolism and link their lifestyles to organic matter supply or phytoplankton. One field expedition is planned to investigate the significance of N2O reduction in the North Atlantic subtropical gyre. If N2O consumption occurs even at low rates over vast regions of the surface ocean, its impact on the overall N2O budget of the ocean and atmosphere could be large.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）是地球大气中的痕量成分。这是一种强大的温室气体，自工业革命以来，其集中度一直在增加，并为总温室效应贡献了约6％。在平流层中的臭氧耗竭中也暗示了N2O。海洋是大气中N2O的净来源。作为氮循环的一部分，微生物在海洋中生产并消耗了N2O。 N2O转化为N2（Dinitrogen Gas）是唯一已知的N2O生物水槽，并被氧强烈抑制的酶催化，因此N2O消耗被认为局限于无氧环境。这是令人惊讶的是，发现N2O消耗的遗传能力在氧气丰富的地面海洋中既存在又活跃。实验表明，去除氧气时，表面海洋微生物迅速消耗N2O。显然，它是呼吸的氧气的替代方法。为什么将这种能力保留在全氧地表水中会有利？这种潜在的N2O消耗是否构成了N2O的实际水槽，这可能会减少N2O从海洋到大气的净转移？将一氧化二氮（N2O）还原为N2被认为是绝对的厌氧过程，通常仅限于水和沉积物中的缺氧环境。先前的工作表明，编码N2O还原酶的基因（NOSZ）在地面海洋中均存在并表达，并且当去除氧气时，表面海洋样品迅速将N2O降低至N2。地表水中的NOSZ基因似乎几乎完全属于不执行非硝化步骤的微生物 - 它们是兼性N2O呼吸器。这里提出的研究将研究可能控制或刺激地表水减少N2O的因素，并表征负责该过程的微生物。实验将检验以下假设：N2O呼吸器是多功能的异嗜性，其活性与有机物供应有关，并且可能与特定材料或与原位原位生产有关的可能性相关。研究人员将执行15N示踪剂孵化，以测量N2O降低速率及其对各种有机底物的反应，包括原位特定材料和新鲜的浮游植物散发物。将使用一组分子生物学方法来确定含NOSZ的微生物的数量和社区组成 - 因为NOSZ基因是如此的潜水员，以至于以前的方法可能低估了其丰度和多样性，并且可能无法确定负责该过程的主要微生物。含NOSZ的微生物的基因组草案将被表征以研究其碳代谢，并将其生活方式与有机物供应或浮游植物联系起来。计划进行一次野外探险，以调查北大西洋亚热带回旋中N2O降低的重要性。如果N2O消费甚至在地表海的广阔地区的速率低时发生，那么它对海洋和大气的整体N2O预算的影响可能很大。该奖项反映了NSF的法定任务，并且被认为值得通过基金会的知识分子优点和更广泛的影响审查标准通过评估来进行评估。