Impact of methanotrophs, methanogens and geochemical conditions on net methane flux to the atmosphere from Arctic soils

在全球范围内，土壤中的碳含量超过了所有植被和大气汇的总和。然而，这种储存的碳不是永久保留的，可以通过生物和非生物机制(称为助熔剂的过程)很容易地释放回大气中。在土壤系统中，微生物群落是碳的主要循环者，包括将土壤碳转化为甲烷(CH4)等气体。这种转化是至关重要的，因为甲烷是第二大温室气体，在过去40年里一直在大气中上升。不幸的是，北极土壤中CH4的释放率似乎在增加，这一点很重要，因为北极过程造成了大气CH4的25%。因此，迫切需要了解和量化影响北极甲烷通量的因素和机制，这将使我们能够更好地预测未来的气候条件。作为背景，我们在2010年量化了斯瓦尔巴特群岛NY-Alesund附近13个不同北极高地的CH4通量，同时测量了近地表土壤的58个地球化学和生物参数(工作重点是厌氧-好氧界面)。然而，统计分析表明，关键的近地表微生物群(即消耗甲烷的甲烷氧化菌和产生甲烷的产甲烷菌)、地球化学条件和检测到的甲烷通量之间的相关性很弱。事实上，数据表明，土壤剖面中更深的现象，包括深层的甲烷生成以及永久冻土融化释放的气体和碳，可能比之前认为的北极土壤净释放CH4更关键。我们现在假设，永久冻土上方生物活动区(BAZ)的深度、非生物永久冻土层的贡献以及厌氧和好氧土层的比例厚度等因素可能会主导观测到的CH4释放速率。具体地说，如果Baz很深，厌氧层相对于有氧层较厚，CH4的产生将超过CH4的消耗，导致CH4进入大气的通量增加。在这个项目中，我们将通过以下活动检验这一替代假设：1.2012年夏末返回纽奥勒索德，以已知和对比CH4通量的特定地点为核心进入巴兹湖及其下方。在这些岩芯中，我们将量化每个地点甲烷和甲烷菌的绝对丰度与深度；确定相关的地球化学条件、CH4和氧气剖面、永冻层深度、永冻层CH4和碳含量；并测量CH4通量，以将土壤和永冻土条件与每个地点释放到大气中的CH4联系起来；2.统计比较每个地点CH4平衡的生物和非生物因素，包括永久冻土CH4和与融化相关的碳释放的影响；3.通过测量远离核心站点的近端站点的CH4通量以更准确地估计不同类型的景观对区域CH4通量的相对贡献，将本地CH4通量估计扩展到NY奥勒苏德周围的景观水平；与一位研究北极甲烷生物-产甲烷菌关系的美国研究人员保持成功的国际合作，以提高当前和未来工作的能力。上述活动将通过为期8个月的研究计划完成，其中包括在纽奥勒索德的NERC北极研究站工作10天。工作将在夏末进行，这是永久冻土融化的最大时期，也是NERC实地站往往未得到充分利用的时候。这一努力的一个核心非技术目标将是获得足够的数据，以支持一项针对欧盟和其他国际融资机构的更大规模的提案。

On a global scale, soils contain more carbon than all vegetation and atmospheric sinks combined. However, this stored carbon is not permanently retained and can be readily released back to the atmosphere by biological and non-biological mechanisms (a process known as flux). In soil systems, microbial communities are the primary recyclers of carbon, including the conversion of soil carbon to gases, such as methane (CH4). This conversion is critical because CH4 is the second most significant greenhouse gas and has been rising in the atmosphere over the past forty years. Unfortunately, rates of CH4 release from Arctic soils appear to be increasing, which is significant because Arctic processes are responsible for > 25% of atmospheric CH4. As such, an urgent need exists to understand and quantify factors and mechanisms that influence Arctic CH4 flux, which will allow us to better predict climate conditions in the future. As background, we quantified CH4 flux at 13 differing high Arctic sites near Ny-Alesund, Svalbard in 2010 in conjunction with the measurement of 58 geochemical and biological parameters in near-surface soils (work focused on the anaerobic-aerobic interface). However, statistical analyses showed only weak correlations among key near-surface microbial groups (i.e., methane-consuming methanotrophs and methane-producing methanogens), geochemical conditions, and detected CH4 flux. In fact, data suggest that phenomena deeper in the soil profile, including deep methanogenesis and gas and carbon releases from melting permafrost, may be more critical than previously thought to net CH4 release from Arctic soils. We now hypothesize that factors such as the depth of the biologically active zone (BAZ) above the permafrost; non-biological permafrost contributions; and the proportional thickness of anaerobic vs. aerobic soil layers may dominate observed CH4 release rates. Specifically, if the BAZ is deep and the anaerobic layer thick relative to the oxic layer, CH4 production will overwhelm CH4 consumption, resulting in elevated CH4 flux to the atmosphere. In this project, we will test this alternate hypothesis via the following activities: 1. Return to Ny-Ålesund in late summer 2012 to core into and below the BAZ at specific sites with known and contrasting CH4 fluxes. Within these cores, we will quantify absolute methanogen and methanotroph abundances versus depth at each site; determine associated geochemical conditions, CH4 and oxygen profiles, permafrost depths, and permafrost CH4 and carbon content; and measure CH4 flux to correlate soil and permafrost conditions with CH4 released to atmosphere at each site; 2. Statistically compare estimated biological vs. non-biological contributors to the CH4 balance at each site, including the influence of permafrost CH4 and carbon releases associated with melting; 3. Extend local CH4 flux estimates to landscape levels around Ny-Ålesund by measuring CH4 flux at proximal sites radiating away from cored sites to more accurately estimate the relative contributions of different types of landscapes to regional CH4 flux; and4. Sustain a successful international collaboration with a USA researcher examining methanotroph-methanogen relationships in the Arctic to increase the capacity of current and future work. The above activities will be fulfilled via an eight-month research plan, including 10 days based at the NERC Arctic Research Station in Ny-Ålesund. Work will be performed in the late summer, which is the period of maximum permafrost thaw, and also a time when the NERC field station tends to be underutilized. A central non-technical goal of this effort will be to gain enough data to support a larger proposal aimed at EU and other international funding agencies.