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，人们对北极条件的变化非常关注。与此同时，我们对冻土带/冻土微生物学和元素循环的理解也存在重大差距。填补这些知识空白将有助于更好地全面了解冻土带，并可以提供有关这一全球重要但脆弱的生态系统将如何应对变化的关键信息。这项研究将填补的特殊知识缺口集中在铁和控制其可获得性的细菌方面。铁是动物、植物和微生物必不可少的微量营养素。它也是某些细菌群体的生长底物，其中许多细菌固定二氧化碳来生长。其中一些细菌与其他产生或消耗甲烷的微生物群体直接竞争，甲烷在大气中的浓度正在继续增加。了解北极二氧化碳和甲烷的动态尤为重要，因为永久冻土中储存了大量有机碳，可以转化为这两种气体。研究小组包括一名在铁循环细菌方面拥有丰富经验的微生物生态学家；一名将量化不同微生物过程的相对影响的数学建模人员；以及一名在永久冻土环境中元素循环方面拥有丰富经验的冻土生态学家。该项目将首次对阿拉斯加S北坡冻土带/永久冻土中负责铁循环的微生物群落进行系统的表征和量化，并加深我们对这些微生物如何通过抑制甲烷产生而与碳循环相互作用的理解。这项研究的基本假设是，北极的条件有利于活跃的铁循环，因为浅层永久冻土层阻止富含铁的水渗入深层含水层(从温带生态系统去除铁的常见途径)。此外，凉爽的水温减缓了铁的化学氧化，而短暂但激烈的生长季提供了一种不稳定碳的来源，有助于促进铁的还原。这些想法将通过在阿拉斯加北坡的图利克野战站进行实地和实验室研究来检验。以前的工作表明，该地区存在与微生物铁垫有关的广泛的铁氧化和铁还原细菌种群，但总的来说，人们对它们的多样性或功能知之甚少。这项工作将利用与栽培无关的、基于扩增的群落分析和元基因组学来进一步表征这些化学合成群落的群落多样性和功能。该研究小组将测量铁循环频率较高的冻土带地点的甲烷产量，并将这些地点与水文和地形相似但铁循环频率较低的地点进行比较，以评估铁循环对甲烷生产和消费的直接影响。这些地点的微生物群也将使用分子分析进行比较。除了这些实地测量，研究人员还将建造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。这将允许受控条件模拟铁和甲烷循环在铁和氧浓度等关键参数可以控制的条件下的相互作用。根据现场和实验室数据，将使用一系列动力学方程建立基于反应的模型。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，这项工作将为培训本科生、研究生以及博士后研究员提供独特的机会，将实地、实验室和基于模型的科学结合起来，以填补我们对冻土带生态系统知识的一个重要空白。为了扩大公众影响力，两位艺术家将被聘请来创造一个独特的艺术-科学对话，这将拓宽对项目结果的解释，并提供博物馆级的创意作品，可以在科学或艺术展览中展示。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.