Collaborative Research: Microbial processes and carbon transformation in the thawing permafrost

由于全球变暖，北极生态系统已经达到了一个“新常态”，其特征是海冰消失，冰川退缩，以及广泛的永久冻土开始融化。永久冻土（即，永久冻土）含有大量的碳，其中大部分以植物碎屑的形式存在。零度以下的温度保护了这种植物来源的碳免受微生物分解。暖化融化消除了这种保护，使永冻层碳暴露于微生物群落的作用下，这些微生物群落将使其降解，并将全球大量的二氧化碳和甲烷（温室气体）“呼吸”到大气中。这种永久冻土碳释放到大气中可能导致更快和更大的气候变化。这将如何发挥作用的细节尚不清楚。这项研究的目的是了解微生物群落如何在冻土融化过程中发挥作用和降解碳。为了实现这一目标，将通过将永久冻土移植到覆盖永久冻土的土壤中来模拟解冻，并在夏季每年解冻。将在多个时间尺度（周、月和年）采集样本。微生物群落和土壤碳化学将在移植前后进行评估，以确定群落在解冻过程中如何变化，功能和降解碳。该研究项目将产生的知识对于了解永久冻土融化产生的温室气体如何有助于未来的气候变化至关重要。除了培养一名研究生和博士后研究员外，该项目还将实施一项新颖的“采用微生物”计划，作为本科实验室课程的一部分。据估计，永久冻土含有全球土壤碳库总量的25-50%。由于全球变暖，到世纪末，高达40%的北方纬度永久冻土可能因融化而消失。永冻层解冻将释放之前冻结的碳，使其易于微生物群落分解。数千年的有机物将转化为二氧化碳和甲烷。由此产生的全球大量CO2和CH 4有可能造成一个放大气候变化影响的正反馈循环。这项研究的总体目标是通过了解解冻永冻土中微生物群落组成、功能和碳周转的规则，更精确地确定这种微生物介导的反馈回路的大小。为了解决这一问题，将进行一系列新的原位解冻实验。将不同年龄的冻土（从全新世和更新世）移植到活动层（每年冻结和解冻的冻土上的土壤）中以模拟解冻。在移植之前，将对土壤进行消毒，然后用来自活性层、来自不同年龄的永久冻土或来自群落组合的微生物群落进行接种，然后在不同的时间间隔进行采样。将评价群落结构（分类标记基因）、功能潜力（宏基因组）、功能（元转录组）和土壤化学（FT-ICR MS，理化测量）。这项研究的结果将是一个综合的概念模型，涉及社区组装和功能，在多个时间尺度解冻过程中的碳周转。该项目将包括本科生、研究生和博士后水平的微生物生态系统生态学研究培训。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

As a result of global warming, arctic ecosystems have reached a ‘new normal’ characterized by the loss of sea ice, retreating glaciers, and the beginning of widespread permafrost thaw. Permafrost (i.e., permanently frozen soil) contains an enormous amount of carbon, much of it in the form of detrital plant material. Subzero temperatures have protected this plant-derived carbon from microbial decomposition. Warming thaw removes this protection, exposing permafrost carbon to the action of microbial communities that will degrade it and ‘breathe’ globally significant amounts of carbon dioxide and methane (greenhouse gases) into the atmosphere. This release of permafrost carbon into the atmosphere could lead to even faster and greater climate change. Details of how this will play out are not well understood. The goal of this research is to understand how microbial communities function and degrade carbon during permafrost thaw. To achieve this goal, thaw will be simulated by transplanting permafrost into soil that overlays the permafrost and thaws annually during the summer months. Samples will be harvested at multiple time scales (weeks, months, and years). Microbial communities and soil carbon chemistry will be evaluated before and after transplantation to determine how communities change, function, and degrade carbon during thaw. The knowledge that will be generated by this research project is critically important to understanding how greenhouse gas production from thawing permafrost will contribute to future climate change. In addition to training a graduate student and postdoctoral researcher the project will also implement a novel "adopt a microbe" program as part of an undergraduate lab course. Estimates are that permafrost contains 25-50% of the total global soil carbon pool. As a result of global warming, up to 40% of northern latitude permafrost may disappear due to thaw by the end of the century. Permafrost thaw will unlock previously frozen carbon making it amenable to microbial community decomposition. Millennia-old organic matter will get converted to CO2 and CH4. The resulting production of globally significant quantities of CO2 and CH4 is likely to cause a positive feedback loop amplifying the effects of climate change. The overarching goal of this research is to more precisely determine the magnitude of this microbe-mediated feedback loop through understanding the rules governing microbial community composition, function, and carbon turnover in the thawing permafrost. To address this a series of novel, in situ thaw experiments will be performed. Permafrost of different ages (from the Holocene and Pleistocene) will be transplanted into the active layer (soil overlaying the permafrost that freezes and thaws annually) to simulate thaw. Prior to transplantation, soils will be sterilized and then inoculated with microbial communities from the active layer, from permafrost of different ages, or from a combination of communities and then sampled at different time intervals. Community structure, (taxonomic marker genes), functional potential (metagenomes), function (metatranscriptomes), and soil chemistry (FT-ICR MS, physicochemical measurements) will be evaluated. The outcome of this research will be an integrated conceptual model that relates community assembly and function to carbon turnover during thaw at multiple time scales. The project will include training in microbial ecosystem ecology research at the undergraduate, graduate and postdoctoral levels.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.