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

据预测，未来几十年，北美东部的年降水量将全面增加，降水事件的强度也将增加。降雨将集中在更少、更大的风暴中，不时出现更长时间的干旱。这种加剧的影响在已经处于水分压力下的盐沼等生态系统中可能尤其重要。盐沼提供关键的生态系统服务，包括鱼类和鸟类的苗圃栖息地和营养过滤。它们还储存了大量的有机碳。降水的变化可能会改变它们的生态，扰乱它们的营养过滤和碳储存活动，其中很大一部分是由盐沼微生物调节的。这项研究的目的是量化降水强化对新英格兰盐沼微生物过程的影响。这项博士论文改进拨款研究还将通过研究环境中微生物的基因表达模式，研究温室气体(CH4和N2O)排放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特别大，无论是在极端干燥的条件下，还是在导致沉积物缺氧的极端潮湿条件下。作为潮汐湿地，盐沼容易受到各种压力因素的影响，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，以测试降水变化对盐沼生物地球化学的影响。雨棚被用来拦截即将到来的降雨，并将其提供给四种降水处理之一：环境降雨、环境降雨加倍、长期干旱或模拟强烈干旱和强风暴。每月测量温室气体、总体生产力和新梢：沼泽草的新梢分配，以及二氧化硅和其他养分在植物、沉积物和孔隙水中的循环。来自该奖项的资金将支持增加一个分子成分。主要目标将是确定1)气候引起的降水变化(长期干旱、生长季节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，2)微生物群落关键功能基因表达的变化在多大程度上可以与测量的微量温室气体通量净速率联系起来。本研究将验证两个假设：(1)长期干旱和加倍的降雨率都会导致微生物物种丰富度下降，但当干旱和降水增加相结合时，这种强化的降水状况将导致微生物物种丰富度的增加。(2)微量温室气体通量(CH4和N2O)与生产功能基因转录本呈正相关，与每种气体的消耗呈负相关。假设1将通过正在进行的野外实验中通过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检验。假设2将通过将高灵敏度气体通量测量与6个控制微生物生产和消耗CH4和N2O的功能基因(MCRA、pmoA、mxaF、nosZ、Norb和norZ)的转录拷贝的定量相结合来验证。拟议的研究将与新的外联活动结合起来。博士生将参与北卡罗来纳大学上行数学和科学项目，该项目为低收入和第一代大学毕业生提供成功的高等教育经历。她将领导一个为期一天的研讨会，与向上的高中生一起讨论盐沼的重要性，以及微生物群落和温室气体之间的联系。她还将主持一个暑期向上的高中生实习生来做这个项目。其次，博士生将在公民科学外联计划中进行协调，该计划利用实验在国家公园经常参观的区域的高能见度位置，让感兴趣的各方参与对实验治疗的监测。

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.