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），因此控制湿地甲烷产生的途径具有全球影响。包括佛罗里达大沼泽地在内的大多数湿地都受到了人类营养添加物的影响。本研究的目的是确定增加营养物质投入，特别是磷酸盐，引起的甲烷产量的提高。磷酸盐和其他营养素导致植物来源的有机物的输入增加，然后在缺氧的湿地土壤中发酵成一系列小分子，最终转化为甲烷。微生物形成甲烷有两条主要途径。全球约70%的淡水湿地产生的甲烷来自乙酸发酵途径，30%来自二氧化碳的还原。初步数据表明，甲烷生成的途径受到磷径流从邻近的农田。指导这项工作的假设是，除了增加植物的有机质产量外，过量的磷酸盐还导致甲烷产量的增加，这是由于影响这些途径的两个额外因素：从与有机生产无关的固氮中提供额外的氢底物供应;以及通过一组不寻常的细菌，互养乙酸盐氧化剂，将乙酸盐衍生的甲烷生产分流到乙酸盐发酵。这种分流有利于二氧化碳还原途径，该途径具有更高的甲烷产生率，对竞争性电子受体（例如硫酸盐）不太敏感，对磷酸盐和铵的抑制不太敏感，并且受到温度升高的不同影响。因此，基于温带湿地的甲烷排放预测可能无法准确预测温暖气候的甲烷排放。将采用微生物、同位素和生物地球化学方法相结合的方法来确定这些途径如何受到营养物污染的影响。将对南佛罗里达和巴拿马的湿地进行检查。该项目的一个重要组成部分是美国和国外未来科学家和中学生的教育。调查人员有长期参与科学教育的记录，从高中到本科，研究生和博士后教育。高中学生将被介绍到各种湿地，包括那些含有食肉植物。该项目不仅将帮助培训佛罗里达大学和佛罗里达州立大学的下一代科学家，而且还将涉及白求恩-库克曼学院（一所以非洲裔美国人为主的小型学院）和当地高中的学生。

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.