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种“新常态”，其特征是海冰减少，冰川退缩，永久冻土开始广泛融化。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不被微生物分解。变暖的解冻消除了这种保护，使永久冻土中的碳暴露在微生物群落的作用下，微生物群落将其降解，并将全球大量的二氧化碳和甲烷（温室气体）“呼吸”到大气中。永久冻土中的碳释放到大气中可能会导致更快、更大的气候变化。这将如何发挥的细节尚不清楚。这项研究的目的是了解微生物群落如何在永久冻土融化期间发挥作用并降解碳。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，并在每年的夏季解冻。样品将在多个时间尺度（周、月、年）采集。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。这项研究项目将产生的知识对于理解永久冻土融化产生的温室气体如何影响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人员外，该项目还将实施一项新颖的“采用微生物”计划，作为本科生实验课程的一部分。据估计，永久冻土包含全球土壤碳库总量的25-50%。由于全球变暖，到本世纪末，多达40%的北纬永久冻土可能会因融化而消失。永久冻土解冻将释放先前冻结的碳，使其易于微生物群落分解。几千年前的有机物会转化成二氧化碳和甲烷。由此产生的全球大量二氧化碳和甲烷很可能造成一个正反馈循环，放大气候变化的影响。本研究的总体目标是通过了解融化的永久冻土中微生物群落组成、功能和碳周转的规则，更精确地确定微生物介导的反馈回路的大小。为了解决这个问题，将进行一系列新颖的原位解冻实验。不同年代的永久冻土（从全新世到更新世）将被移植到活动层（覆盖在每年冻结和融化的永久冻土上的土壤）来模拟解冻。在移植之前，将对土壤进行灭菌，然后用来自活动层、不同年龄的永久冻土或群落组合的微生物群落接种，然后在不同的时间间隔取样。将对群落结构（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）进行评估。本研究的结果将是一个综合的概念模型，该模型将在多个时间尺度上将群落组装和功能与解冻期间的碳周转联系起来。该项目将包括对本科生、研究生和博士后进行微生物生态系统生态学研究的培训。该奖项反映了美国国家科学基金会的法定使命，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.