Collaborative Research: Shifting pathways toward methane in nutrient impacted tropical and sub-tropical wetlands

淡水湿地是大气中甲烷的最大单一来源。甲烷是一种强有力的温室气体(大约是二氧化碳的24倍)，因此控制湿地甲烷生产的途径具有全球影响。大多数湿地，包括佛罗里达大沼泽地，都受到人类来源的营养物质添加的影响。这项研究的目标是确定增加营养投入，特别是磷酸盐，对甲烷产量的促进作用。磷酸盐和其他营养物质导致植物衍生有机物质的输入增加，然后在缺氧湿地土壤中发酵成一系列小分子，最终转化为甲烷。微生物形成甲烷的主要途径有两条。全球淡水湿地产生的甲烷中，约70%来自醋酸盐发酵途径，30%来自二氧化碳还原。初步数据表明，产甲烷途径受到邻近农田磷素径流的影响。指导这项工作的假设是，除了增加植物的有机质生产外，过量的磷酸盐还会导致甲烷产生速率更高，这是因为影响这些途径的另外两个因素：与有机生产无关的固氮提供额外的氢底物；以及一组不寻常的细菌--合养乙酸酯氧化菌--将乙酸盐甲烷产生的甲烷分流到乙酸酯的发酵中。这种分流有利于二氧化碳还原途径，该途径具有较高的甲烷生成率，对竞争性电子受体(如硫酸盐)不太敏感，对磷酸盐和铵的抑制较不敏感，并且受温度升高的影响不同。因此，基于温带湿地的甲烷排放预测可能无法准确预测气候变暖的甲烷排放。将采用微生物学、同位素和生物地球化学相结合的方法来确定这些途径如何受到营养污染的影响。将对佛罗里达州南部和巴拿马的湿地进行检查。该项目的一个重要组成部分是对美国和国外未来科学家和中学生的教育。调查人员长期参与科学教育，从高中到本科生、研究生和博士后教育。高中生将被介绍到各种湿地，包括那些含有食肉植物的湿地。该项目不仅将帮助培养佛罗里达大学和佛罗里达州立大学的下一代科学家，还将吸引以非裔美国人为主的小型学院白求恩-库克曼学院和当地高中的学生参与。

Freshwater wetlands are the largest single source of methane to the atmosphere. Methane is a potent greenhouse gas (approximately 24 times more potent than carbon dioxide), such that the pathways that control the production of methane in wetlands have global implications. Most wetlands, including the Florida Everglades, are affected by human-derived nutrient additions. The goal of this research is to determine the enhancement of methane production caused by increased nutrient inputs, particularly phosphate. Phosphate and other nutrients result in increased inputs of plant derived-organic matter, which is then fermented to an array of small molecules in anoxic wetland soils, which are eventually converted to methane. There are two main pathways by which microbes form methane. Approximately 70% of global freshwater wetland-produced methane arises from the acetate fermentation pathway and 30% comes from reduction of carbon dioxide. Preliminary data indicate that pathways for methanogenesis are affected by phosphorus runoff from adjacent agricultural lands. Guiding this work is the hypothesis that in addition to increasing organic matter production by plants, excess phosphate also results in higher rates of methane production due to two additional factors affecting these pathways: provision of additional supply of hydrogen substrate from nitrogen fixation that is unrelated to organic production; and shunting of methane production from acetate-derived methane to fermentation of acetate by an unusual group of bacteria, the syntrophic acetate oxidizers. This shunting benefits the carbon dioxide reduction pathway which has higher rates of methane production, is less sensitive to competitive electron acceptors (such as sulfate), is less sensitive to phosphate and ammonium inhibition, and is affected differently by increased temperature. Thus predictions of methane emissions based on temperate wetlands may not accurately forecast methane emissions from warmer climates. A combination of microbiological, isotopic and biogeochemical approaches will be employed to determine how these pathways are affected by nutrient pollution. Wetlands in South Florida and Panama will be examined. An important component of this project is the education of future scientists and secondary school students in the United States and abroad. The investigators have long records of involvement in science education ranging from high schools to undergraduate, graduate and post doctoral education. High school students will be introduced to a variety of wetlands including those containing carnivorous plants. The project will aid not only in training the next generation of scientists at the University of Florida and Florida State University, but will also will involve students from Bethune-Cookman College, a small predominantly African American college, and local high schools.