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。零度以下的温度使永久冻土微生物群落不受上覆活土层过程的影响，并保护永久冻土的碳储量不受微生物转化的影响。然而，气候变暖增加了永久冻土融化的速度和程度，增加了有机碳的生物有效性和碳代谢率。这些变化将以二氧化碳和甲烷的形式释放大量的碳储量，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。在景观水平上，永久冻土群落是由同质选择形成的，由于永久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，永久冻土微生物群落在短空间尺度上可能发生变化，主要受扩散限制的影响，这限制了永久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征可能成为新融化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，变量选择将成为一个主导的生态过程，驱动群落对可变环境条件的响应，永久冻土上覆土壤中生物群落的当代空间格局将很好地预测解冻后群落特征和过程速率。然而，目前还没有研究在大空间尺度上考察永久冻土微生物群落与活动层土壤群落的模式，也没有研究试图模拟永久冻土融化时永久冻土与上覆土壤之间的相互作用将如何影响这些尺度上的群落结构和功能。拟议研究的目的是提高对影响加拿大北部环境中永久冻土和活动层土壤中微生物分布的生态过程的理解，并利用这些知识来预测这些生态系统将如何对永久冻土解冻作出反应。提出的研究将探讨以下问题：Q1)活动层和永久冻土微生物群落组成的模式是否可以用北极和亚北极景观的环境变化来解释？Q2)解冻前永久冻土微生物群落的特征在多大程度上影响对永久冻土解冻的响应？Q3)解冻前环境的各个方面是否可以用来预测解冻后微生物群落功能和碳循环动态？这项工作将提高对加拿大北部活土层和永久冻土微生物多样性的理解，塑造这些群落的生态过程，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.