Microbial succession from ice to vegetated soils in response to glacial retreat

当冰川退缩时，它们的前田提供了一个独特的机会来研究土壤形成和微生物演替的初始阶段。随着冰层的消退，为微生物和植物的定居留下了空间，一些研究表明，在达到一定的土壤稳定性之前，与多年的暴露有关的各种微生物代理物，如固氮，微生物酶活性和多样性增加。令人惊讶的是，人们对北极栖息地微生物的遗传和功能多样性知之甚少。整个微生物种群的组成和代谢潜力可以通过使用宏基因组方法直接从环境中回收的遗传物质进行分离和表征来探索。每一个被分析的土壤栖息地样本都代表了不同微生物类型复杂混合的快照，某些类型的微生物比其他类型的微生物要丰富得多。例如，我们在本项目中预测，与光养C和N固定以及有氧C代谢相关的基因将在冰川消退后的土壤演替的初始阶段占主导地位，而更深的土壤样品将为厌氧C和N代谢的发展提供条件，包括产生和消耗甲烷，这是一种非常强大的温室气体。宏基因组学方法可以进一步与土壤的代谢速率和地球化学特征联系起来，这些因素中的许多因素相互之间具有很强的反馈作用。将微生物多样性与生态系统功能和关键元素（C、N、Fe）的地球化学循环联系起来的研究很少。该提案旨在采用这种综合方法，生成新的和独特的北极陆地代表性生境的遗传和功能多样性数据集。该项目将激发我们对陆地北极栖息地代谢途径的理解，以改善冰川退缩后土壤连续事件期间的生物地球化学模型和完整代谢包的量化。本项目将选择两个冰川的前地（一个在斯瓦尔巴特群岛，一个在格陵兰岛，分别代表一个小型极地系统和一个主要冰盖），因为它们提供了一系列不同大小、位置、植被和系统周围水的可用性的前地栖息地。用于宏基因组分析的样品将取自代表冰川退缩后不同暴露年龄的代表性土壤。我们的目标是生成比现有宏基因组管道最初设计处理的多几个数量级的初级序列数据。这种采样策略将为我们提供与关键元素（例如，C，N，Fe）的冰川前田栖息地，也使我们能够预测的变化，代谢途径和地球化学循环，以应对冰川退缩。该项目将促使我们对冰川北极陆地栖息地生物多样性的理解有一个飞跃，并提供一个数据库，可用于解释未来恢复的数据。这将最终为我们提供有关其他冰冷行星和卫星以及所谓的雪球地球中生命潜力的宝贵见解。该提案中产生的数据可纳入碳、氮、铁和硫循环模型。

When glaciers retreat, their forefields present a unique opportunity to investigate the initial phases of soil formation and microbial succession. As the ice retreats leaving space for microbial and plant colonisation, some studies show evidence of an increase in a variety of microbial proxies, such as nitrogen fixation, microbial enzymatic activity and diversity, in relation to years of exposure until certain soil stability is reached. Surprisingly, very little is known regarding the genetic and functional diversity of microbes in Arctic habitats. The composition and the metabolic potential of the entire microbial population can be explored by isolating and characterising their genetic material recovered directly from the environment using a metagenomic approach. Each sample of a soil habitat analysed represents a snapshot of the complex mixture of different microbial types and some types will be much more abundant than others. For instance, we predict in this project that genes associated with phototrophic C and N fixation and aerobic C metabolism will be predominant at the initial stages of succession in soil after glacial retreat, while deeper soil samples will provide conditions for anaerobic C and N metabolism to develop, include the production and consumption methane, which is a very powerful greenhouse gas. The metagenomic approach can be further linked to rates of metabolism and geochemical characteristics of soils, many of those factors have strong feedbacks with each other. There have been few integrated studies which link microbial diversity to ecosystem function and the biogeochemical cycling of key elements (C, N, Fe). This proposal aims to employ such integrated approach to generate new and uniquely datasets of genetic and functional diversity of representative terrestrial Arctic habitats. The project will instigate a step jump in our understanding of metabolic pathways of terrestrial Arctic habitats to improve biogeochemical models and quantification of the full metabolic package during successional events in soils after glacial retreat. The forefields of 2 glaciers (one in Svalbard and one in Greenland, which represent one small polar system and one major ice sheet, respectively) will be chosen for this project because they provide a range of forefield habitats of different sizes, locations, vegetation and availability of water surrounding the system. Samples for the metagenomic analyses will be taken from representative soils representing different ages of exposure after glacial retreat. We aim to generate several orders of magnitude more primary sequence data than existing metagenome pipelines were originally designed to deal with. This sampling strategy will give us a high-resolution picture of the microbial genetic and metabolic diversity associated with key elements (e.g., C, N, Fe) of glacial forefield habitats, also allowing us to PREDICT changes in metabolic pathways and biogeochemical cycles in response to glacial retreat. The project will instigate a step jump in our understanding of the biodiversity of glacial Arctic terrestrial habitats and provide a database that may be used to interpret data recovered during future. This will ultimately give us valuable insights in relation to the potential for life in other icy planets and moons and during the so called Snowball Earth. Data generated in this proposal can be incorporated into models of carbon, nitrogen, iron and sulphur cycling.