Collaborative Research: MSB: The Role of Sulfur Oxidizing Bacteria in Salt Marsh C and N Cycling

合作研究：MSB：硫氧化细菌在盐沼碳氮循环中的作用

• 批准号: 1050557
• 负责人: Stefan Sievert
• 金额: $ 69万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1050557&HistoricalAwards=false
• 关键词: Collaborative; Research; MSB; Role; Sulfur

Salt marshes are extraordinarily productive ecosystems found in estuaries worldwide. Located between the coastal ocean and coastal watersheds, salt marshes are often heavily influenced by human activities. Many receive high nitrate input from land, degrading water quality and leading in some cases to harmful algal blooms and low oxygen zones harmful to fish. Previous research has shown that salt marshes can act as cleansing sites where pollutant nitrate can be transformed to harmless nitrogen gas and released to the atmosphere. This occurs through heterotrophic denitrification, a microbe-mediated process that transforms plant-available nitrate to nitrogen gas (N2) using organic carbon. However, this transformation to harmless nitrogen gas is not always the fate of salt marsh nitrate. More recent research suggests that the forms of sulfur and carbon compounds in the marsh sediment directly affect the types of microbes and their activities determining nitrate?s fate, i.e. sulfur, nitrogen, and carbon transformations are all linked via microbial activities. For example, instead of being converted to nitrogen gas, nitrate can be converted to ammonium via the microbially controlled process dissimilatory nitrate reduction (DNRA). This different fate of nitrate is environmentally important in several ways. If nitrate is converted to nitrogen gas, it is lost from the ecosystem to the atmosphere, whereas if DNRA dominates nitrate reduction, pollutant nitrogen remains in the system as ammonium. Also, depending on the type of microbial process governing nitrate?s fate, if organisms are using nitrate to help degrade organic matter, less carbon is stored in the ecosystem, potentially influencing the ability of marshes to keep up with sea level rise. To investigate the environmental and microbial controls affecting the fate of nitrate in salt marshes, lab and field experiments will be carried out at Plum Island Estuary. The project focuses on sulfur-oxidizing bacteria, a group of particularly important chemosynthetic microbes that use energy trapped in sulfur compounds in sediment to for energy production, and thus contribute to carbon storage. The proposed studies aim (1) to identify sulfur-oxidizers present in sediment densely populated with the salt marsh grass, Spartina alterniflora, and to examine their gene expression linked to sulfur and nitrate processing under shifting environmental conditions; and (2) to combine this molecular information with measurements of rates and characteristics of biogeochemical reactions occurring in the sediment to detect whether sulfur-oxidizer-linked DNRA (thus retention of nitrogen in the ecosystem) or denitrification (thus loss of nitrogen gas from the ecosystem) dominates under specific environmental conditions.Broader Impacts. This multidisciplinary research integrates biogeochemical process measurements with molecular analyses, and will be synergistic with ongoing studies at the Plum Island Ecosystem Long-Term Ecological Research (PIE-LTER) site. Salt marshes provide a variety of ecosystem services to humanity, including nutrient removal and storm protection, but they are under pressure from increasing coastal development and rising sea level. A detailed understanding of marsh microbial function will likely contribute to restoration efforts, particularly if the form of sulfur present in marshes allows prediction of whether pollutant nitrogen will most likely be lost (as nitrogen gas) or retained over time. Project personnel will participate as research supervisors or teachers in MBL?s annual fall Semester in Environmental Science, which each year draws mostly women from undergraduate liberal arts colleges into rigorous classroom learning and individual ecosystems research. One post-doc will also be trained in this interdisciplinary atmosphere, and collaboration between PIE-LTER and Massachusetts Audubon Society provides a conduit for the investigators to teach middle and high school students about nitrogen loading from human activities on land, and its effects in local estuaries.

盐沼是世界各地河口地区极其富饶的生态系统。盐沼位于沿海海洋和沿海流域之间，经常受到人类活动的严重影响。许多国家从陆地接收大量硝酸盐，导致水质恶化，在某些情况下导致有害藻华和对鱼类有害的低氧区。先前的研究表明，盐沼可以作为净化场所，污染物硝酸盐可以转化为无害的氮气并释放到大气中。这是通过异养反硝化作用发生的，异养反硝化是一种微生物介导的过程，利用有机碳将植物可利用的硝酸盐转化为氮气 (N2)。然而，这种向无害氮气的转变并不总是盐沼硝酸盐的命运。最近的研究表明，沼泽沉积物中硫和碳化合物的形式直接影响微生物的类型及其决定硝酸盐命运的活动，即硫、氮和碳的转化都通过微生物活动联系在一起。例如，硝酸盐可以通过微生物控制的异化硝酸盐还原过程（DNRA）转化为铵，而不是转化为氮气。硝酸盐的这种不同命运在几个方面对环境具有重要意义。如果硝酸盐转化为氮气，它就会从生态系统流失到大气中，而如果 DNRA 主导硝酸盐还原，污染物氮将以铵的形式保留在系统中。此外，根据控制硝酸盐命运的微生物过程的类型，如果生物体使用硝酸盐来帮助降解有机物，生态系统中储存的碳就会减少，这可能会影响沼泽跟上海平面上升的能力。为了研究影响盐沼中硝酸盐命运的环境和微生物控制，将在普拉姆岛河口进行实验室和现场实验。该项目的重点是硫氧化细菌，这是一组特别重要的化学合成微生物，它们利用沉积物中硫化合物中捕获的能量来生产能量，从而有助于碳储存。拟议的研究旨在（1）识别盐沼草、互花米草密集的沉积物中存在的硫氧化剂，并检查它们在不断变化的环境条件下与硫和硝酸盐加工相关的基因表达； (2) 将这些分子信息与沉积物中发生的生物地球化学反应的速率和特征的测量相结合，以检测与硫氧化剂相关的 DNRA（从而在生态系统中保留氮）或反硝化（从而从生态系统中损失氮气）是否在特定环境条件下占主导地位。更广泛的影响。这项多学科研究将生物地球化学过程测量与分子分析相结合，并将与普拉姆岛生态系统长期生态研究（PIE-LTER）站点正在进行的研究产生协同作用。盐沼为人类提供了多种生态系统服务，包括营养物去除和风暴防护，但它们面临着沿海开发和海平面上升的压力。对沼泽微生物功能的详细了解可能有助于恢复工作，特别是如果沼泽中存在的硫的形式可以预测污染物氮是否很可能会随着时间的推移而消失（作为氮气）或保留。项目人员将作为研究主管或教师参加 MBL 年度秋季环境科学学期，该学期每年都会吸引大多数来自文理学院本科生的女性参加严格的课堂学习和个体生态系统研究。一名博士后也将在这种跨学科氛围中接受培训，PIE-LTER 和马萨诸塞州奥杜邦协会之间的合作为研究人员提供了一个渠道，让研究人员向中学生和高中生传授陆地上人类活动产生的氮负荷及其对当地河口的影响。