Dissertation Research: The effects of precipitation change on microbial drivers of salt marsh greenhouse gas emissions

论文研究：降水变化对盐沼温室气体排放微生物驱动因素的影响

• 批准号: 1501721
• 负责人: Robinson Fulweiler
• 金额: $ 2.02万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1501721&HistoricalAwards=false
• 关键词: Dissertation; Research; effects; precipitation; change

It is predicted that, in the next several decades, Eastern North America will experience an overall increase in annual precipitation, as well as an increase in the intensity of precipitation events. Rainfall will be concentrated into fewer, larger storms punctuating longer periods of drought. The effects of this intensification may be especially important in ecosystems like salt marshes, that are already under water stress. Salt marshes provide critical ecosystem services including nursery habitat for fish and birds, and nutrient filtration. They also store vast amounts of organic carbon. Changes in precipitation may alter their ecology, and disrupt their nutrient filtration and carbon storage activities, much of which is mediated by salt marsh microorganisms. The objective of this research is to quantify the effects of precipitation intensification on on microbial processes in a New England salt marsh. This doctoral dissertation improvement grant research will also examine mechanisms behind patterns of greenhouse gas (CH4 and N2O) emissions and uptake by salt marsh microbes by studying microbial gene expression patterns in the environment. Precipitation changes, especially the intensification of precipitation events (e.g. longer droughtsand stronger storms) are an important aspect of anthropogenic global climate change. The impact of precipitation intensification may be especially great in ecosystems that are chronically water stressed, either from extremely dry conditions, or from extremely wet conditions that lead to anoxia in the sediment. As tidal wetlands, salt marshes are subject to a variety of stressors including high salinity and anoxia, making them potentially very sensitive to changes in rain and other freshwater inputs. Over the past year an experiment has been performed to test the effects of precipitation change onsalt marsh biogeochemistry. Rainout shelters have been used to intercept incoming rain, and deliver it to one of four precipitation treatments: ambient rainfall, doubled ambient rainfall, prolonged drought, or simulated intense drought with strong storms. Monthly measurements were made of greenhouse gases, the overall productivity and shoot:shoot allocation of marsh grasses, and the cycling of silica and other nutrients through plants, sediment, and porewater. Funding from this award will support the addition of a molecular component. The primary objectives will be to determine 1) whether climate-induced changes in precipitation (prolonged drought, doubled growing season totals, or alteration between the two) will alter salt marsh microbial community structure and species richness, and 2) to what degree changes in the expression of key functional genes by the microbial community can be linked to measured net rates of trace greenhouse gas flux. This research will test two hypotheses: (1) Prolonged drought and doubled precipitation rates will both lead to decreases in microbial species richness, but when drought and increased precipitation are combined this intensified precipitation regime will lead to an increase in microbial species richness, and (2) trace greenhouse gas fluxes (CH4 and N2O) are positively correlated with functional gene transcript copies for production and negatively correlated with those for consumption of each gas. Hypothesis 1 will be tested by determining microbial community composition and species richness with next-generation sequencing of genomic DNA in sediments at an ongoing field experiment. Hypothesis 2 will be tested by pairing high-sensitivity gas flux measurements with quantification of transcript copies of 6 functional genes (mcrA, pmoA, mxaF, nosZ, norB, and norZ) governing microbial production and consumption of CH4 and N2O. The proposed research will be integrated with new outreach activities. A Ph.D. student will work with the BU Upward Bound Math and Science program, which prepares low-income and first generation college bound students for a successful higher education experience. She will lead a one-day workshop with Upward Bound high school students on the importance of salt marshes, and the linkages between microbial communities and greenhouse gases. She will also host a summer Upward Bound high school student intern to work on this project. Second, the Ph.D. student will coordinate in a Citizen Science Outreach Program that leverages the experiment's high-visibility location in a frequently-visited area of a National Park to involve interested parties in the monitoring of the experimental treatments.

预计未来几十年，北美东部年降水量将全面增加，降水事件强度也将增加。降雨将集中为数量更少、规模更大的风暴，从而加剧干旱期的延长。这种集约化的影响对于盐沼等已经面临缺水压力的生态系统可能尤其重要。 盐沼提供重要的生态系统服务，包括鱼类和鸟类的繁殖栖息地以及营养物过滤。它们还储存大量的有机碳。 降水量的变化可能会改变它们的生态，并破坏它们的营养过滤和碳储存活动，其中大部分是由盐沼微生物介导的。 本研究的目的是量化降水加剧对新英格兰盐沼微生物过程的影响。 这项博士论文改进资助研究还将通过研究环境中的微生物基因表达模式来研究温室气体（CH4 和 N2O）排放模式和盐沼微生物吸收模式背后的机制。降水变化，特别是降水事件的加剧（例如更长的干旱和更强的风暴）是人为全球气候变化的一个重要方面。在长期缺水的生态系统中，降水加剧的影响可能尤其严重，无论是由于极端干燥的条件，还是由于极端潮湿的条件导致沉积物缺氧。作为潮汐湿地，盐沼受到各种压力源的影响，包括高盐度和缺氧，这使得它们对降雨和其他淡水输入的变化非常敏感。在过去的一年里，进行了一项实验来测试降水变化对盐沼生物地球化学的影响。防雨棚已被用来拦截即将到来的降雨，并将其输送到四种降水处理之一：环境降雨、环境降雨量加倍、长期干旱或模拟强烈干旱和强风暴。每月测量温室气体、沼泽草的整体生产力和芽与芽的分配，以及二氧化硅和其他营养物质通过植物、沉积物和孔隙水的循环。该奖项的资金将支持添加分子成分。主要目标是确定 1) 气候引起的降水变化（长期干旱、生长季总量翻倍或两者之间的变化）是否会改变盐沼微生物群落结构和物种丰富度，以及 2)微生物群落关键功能基因的表达可以与测量的痕量温室气体通量的净速率联系起来。这项研究将检验两个假设：（1）长期干旱和降水率加倍都会导致微生物物种丰富度下降，但当干旱和降水增加结合在一起时，这种强化的降水状况将导致微生物物种丰富度增加，并且（ 2) 微量温室气体通量（CH4 和 N2O）与生产的功能基因转录本拷贝数呈正相关，与每种气体的消耗的功能基因转录本拷贝数呈负相关。假设 1 将通过在正在进行的现场实验中对沉积物中的基因组 DNA 进行下一代测序来确定微生物群落组成和物种丰富度来进行检验。假设 2 将通过将高灵敏度气体通量测量与控制微生物产生和消耗 CH4 和 N2O 的 6 个功能基因（mcrA、pmoA、mxaF、nosZ、norB 和norZ）的转录本定量结合起来进行检验。拟议的研究将与新的外展活动相结合。博士学位学生将参与波士顿大学向上发展数学和科学项目，该项目为低收入和第一代大学学生准备成功的高等教育经历。她将与 Upward Bound 高中生一起主持为期一天的研讨会，讨论盐沼的重要性以及微生物群落与温室气体之间的联系。她还将接待一名暑期Upward Bound高中生实习生来从事该项目。第二，博士学位。学生将协调一项公民科学外展计划，该计划利用该实验在国家公园经常访问的地区的高可见度位置，让感兴趣的各方参与对实验治疗的监测。