NNA: Collaborative Research: Interactions of the Microbial Iron and Methane Cycles in the Tundra Ecosystem

由于环境变化正在影响冻土带及其下面的永久冻土，人们对北极不断变化的条件非常关注。与此同时，我们对冻土带/永久冻土微生物学和元素循环的理解存在重大差距。填补这些知识空白将使人们能够更好地全面了解冻土带，并可以提供关于这一具有全球重要性但脆弱的生态系统将如何应对变化的关键信息。这项研究将填补围绕铁和控制其可用性的细菌的特定知识空白。铁是动物、植物和微生物必需的微量营养素。它还可以作为某些细菌群的生长基质，其中许多细菌可以固定二氧化碳来生长。其中一些细菌直接与产生或消耗甲烷的其他微生物群竞争，大气中甲烷的浓度正在持续增加。了解北极地区二氧化碳和甲烷的动态变化尤为重要，因为永久冻土中储存着大量的有机碳，可以转化为这两种气体。研究团队由一名在铁循环细菌方面具有丰富经验的微生物生态学家组成；一个数学建模者，他将量化不同微生物过程的相对影响，一个冻土带生态学家，在永久冻土环境中元素循环方面有丰富的经验。该项目将首次系统地描述和量化阿拉斯加冻土带/永久冻土中负责铁循环的微生物群落。并增加我们对这些微生物如何通过抑制甲烷产生与碳循环相互作用的理解。本研究的基本假设是，北极的条件有利于活跃的铁循环，因为浅层深度的永久冻土阻止含铁的水渗透到深层含水层（温带生态系统中铁去除的常见途径）。此外，凉爽的水温减缓了铁的化学氧化，短暂但强烈的生长季节提供了一种有助于铁还原的不稳定碳的来源。这些想法将通过在阿拉斯加北坡的图里克野外站进行实地和实验室研究来验证。先前的研究表明，该地区存在大量与微生物铁垫相关的铁氧化和铁还原细菌，但总的来说，对它们的多样性或功能知之甚少。本研究将利用培养不依赖、基于扩增子的群落分析和宏基因组学进一步表征这些化学合成群落的多样性和功能。研究小组将测量铁循环率高的冻土带地区的甲烷产量，并将这些地区与水文和地形相似但铁循环率较低的地区进行比较，以评估铁循环对甲烷生产和消耗的直接影响。这些地点的微生物组也将使用分子分析进行比较。除了这些实地测量之外，研究人员还将构建一个实验室微观世界，可以用从Toolik收集的土壤和微生物铁垫播种。这将允许在控制条件下模拟铁和甲烷循环的相互作用，其中关键参数如铁和氧浓度可以控制。根据现场和实验室数据，将利用一系列动力学方程建立一个基于反应的模型。这些将构成一个预测模型的基础，该模型可以估计铁循环对甲烷产生的抑制作用。就更广泛的影响而言，这项工作将为培养本科生、研究生以及博士后研究人员提供独特的机会，将实地、实验室和基于建模的科学结合起来，填补我们对冻土带生态系统知识的重要空白。为了扩大公众宣传，两位艺术家将参与创造一个独特的艺术与科学对话，这将扩大对项目结果的解释，并提供博物馆质量的创造性作品，可以在科学或艺术展览中展示。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。

There is great concern about changing conditions in the Arctic due to environmental transformations that are impacting tundra and its underlying permafrost. At the same time there are major gaps in our understanding of tundra/permafrost microbiology and elemental cycling. Filling these knowledge gaps will enable a better overall understanding of the tundra, and can provide crucial information about how this globally important, but fragile ecosystem will respond to change. The particular knowledge gap this research will fill centers around iron and the bacteria that control its availability. Iron is an essential micro-nutrient for animals, plants, and microbes. It also serves as a growth substrate for certain groups of bacteria, many of which fix carbon dioxide to grow. Some of these bacteria directly compete with other groups of microbes that produce or consume methane, the atmospheric concentration of which is continuing to increase. It is particularly important to understand the dynamics of carbon dioxide and methane in the Arctic because there is a large amount of organic carbon stored in permafrost that could be converted into these two gases. The research team consists of a microbial ecologist with considerable experience in iron cycling bacteria; a mathematical modeler who will quantify the relative impacts of different microbial processes, and a tundra ecologist with extensive experience in elemental cycling in permafrost environments. This project will, for the first time, systematically characterize and quantify microbial communities responsible for iron cycling in the tundra/permafrost of Alaska?s North Slope, and increase our understanding of how these microbes interact with the carbon cycle by suppressing methane production. The basic supposition of this research is that conditions in the Arctic are beneficial to an active iron cycle because the shallow depth permafrost prevents ferrous iron-laden waters from percolating into deep aquifers (a common route for iron removal from temperate ecosystems). Furthermore, cool water temperatures slow the chemical oxidation of iron, and a short, but intense growing season provides a source of labile carbon that helps fuel iron reduction. These ideas will be tested by conducting field and laboratory studies at the Toolik Field Station on the North Slope of Alaska. Previous work has revealed there are extensive populations of iron-oxidizing and iron-reducing bacteria associated with microbial iron mats in this region, but in general, little is known about their diversity or function. This work will utilize cultivation-independent, amplicon-based community analysis and metagenomics to further characterize community diversity and function among these chemosynthetic communities. The team will measure methane production at tundra sites with high rates of iron cycling and compare these to sites that are similar in terms of hydrology and landform, but have lower rates of iron-cycling to assess the direct impact of the iron cycle on methane production and consumption. The microbiomes of these sites will also be compared using molecular analysis. In addition to these field measurements, the researchers will construct a laboratory microcosm that can be seeded with soils and microbial iron mats collected from Toolik. This will allow controlled conditions to simulate interactions of the iron and methane cycles under conditions where key parameters such as iron and oxygen concentrations can be controlled. From both field and laboratory data a reaction-based model will be developed using a series of kinetic equations. These will form the basis for a predictive model that can estimate the suppressive effects of iron cycling on methane production. In terms of broader impacts, the work will provide unique opportunities for training undergraduate, and graduate students, as well as a postdoctoral researcher, in combining field, laboratory, and modelling based science to fill an important gap in our knowledge of the tundra ecosystem. To broaden public outreach two artists will be engaged to create a unique art-science dialog that will broaden the interpretation of the project results, and provide museum quality creative work that can be displayed in either science or art exhibits.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.