Predicting permafrost microbial community responses to thaw based on pre-thaw ecosystem characteristics

永久冻土环境是地球上最重要的碳库之一。零度以下的温度将冻土微生物群落与上覆的活性层过程隔离开来，并保护冻土碳储存免受微生物转化的影响。然而，气候变暖正在增加冻土融化的速度和程度，增加有机碳的生物利用度和碳代谢率。这些变化将释放大量的碳储存，如二氧化碳和甲烷，增加对气候变暖的积极反馈。这些变化的速率和幅度取决于微生物过程，受控制微生物群落动态的生态过程的影响。在景观层面，永冻土群落是由同质选择塑造的，由于永冻土环境的共同选择压力，这使得群落看起来更加相似。然而，多年冻土微生物群落可以在短的空间尺度上变化，主要是受扩散限制的影响，限制了多年冻土微生物群落的混合。这表明，随着扩散限制的解除，上覆土壤的生物和物理化学特性可能成为新解冻的永久冻土中微生物群落结构和功能的重要驱动因素。如果是这样的话，变量选择将成为一个主导的生态过程，驱动社区的变化，以应对多变的环境条件下，和当代的空间格局的生物群落覆盖多年冻土层的土壤将是很好的预测后-解冻社会的特点和过程速率。然而，还没有研究探讨模式的冻土微生物群落沿着与活跃层土壤群落在大的空间尺度或试图模拟冻土和上覆土壤之间的相互作用将如何影响在这些尺度上的群落结构和功能的冻土解冻。拟议的研究的目的是提高认识的生态过程影响微生物分布在冻土和活性层土壤在加拿大的北方环境，并利用这些知识来预测这些生态系统将如何应对冻土融化。拟议的研究将调查以下问题：Q1）北极和亚北极景观的环境变化能否解释活动层和永久冻土微生物群落组成的模式？解冻前冻土微生物群落的特征在多大程度上影响冻土解冻的反应？Q3）解冻前环境的各个方面可以用来预测解冻后微生物群落功能和碳循环动态吗？这项工作将提高对加拿大北方活动层和永久冻土的微生物多样性的理解，塑造这些社区的生态过程，以及它们对加拿大北极加速变暖的潜在反应。

Permafrost environments are among the most important carbon reservoirs on Earth. Sub-zero temperatures isolate permafrost microbial communities from overlying active layer processes, and protect permafrost carbon stores from microbial transformations. However, climate warming is increasing the rate and extent of permafrost thaw, increasing organic carbon bioavailability and carbon metabolism rates. These changes will liberate vast carbon stocks as carbon dioxide and methane, increasing positive feedbacks on climate warming. The rate and magnitude of these changes are dependent on microbial processes, influenced by the ecological processes that govern microbial community dynamics. At the landscape level, permafrost communities are shaped by homogeneous selection, which drives communities to look more similar as a result of shared selective pressures of the permafrost environment. However, permafrost microbial communities can vary over short spatial scales, influenced primarily by dispersal limitation which limits mixing of permafrost microbial communities. This suggests that, as dispersal constraints are relieved, biological and physicochemical characteristics of the overlying soils may become important drivers of microbial community structure and function in newly thawed permafrost. If so, variable selection will become a dominant ecological process, driving community variation in response to variable environmental conditions, and contemporary spatial patterns of biological communities in soils overlying permafrost will be good predictors of post--thaw community characteristics and process rates. However, no studies have examined patterns of permafrost microbial communities along with active layer soil communities over large spatial scales or attempted to model how interactions between permafrost and overlying soils will influence community structure and function at these scales as permafrost thaws. The objective of the proposed research is to improve understanding of the ecological processes influencing microbial distributions in permafrost and active layer soils across Canada's northern environments, and to use this knowledge to predict how these ecosystems will respond to permafrost thaw. The proposed research will investigate the following questions: Q1) Can patterns of active layer and permafrost microbial community composition be explained by environmental variation across Arctic and Subarctic landscapes? Q2) To what degree do characteristics of the pre--thaw permafrost microbial community influence responses to permafrost thaw? Q3) Can aspects of the pre-thaw environment be used to predict post--thaw microbial community function and carbon cycling dynamics? This work will improve understanding of the microbial diversity of active layer and permafrost soils across northern Canada, the ecological processes shaping these communities, and their potential responses to the accelerated warming of Canada's Arctic.