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

在全球范围内，土壤所含的碳比所有植被和大气汇的总和还要多。然而，这种储存的碳并不是永久保留的，可以通过生物和非生物机制（一种称为通量的过程）容易地释放回大气。在土壤系统中，微生物群落是碳的主要回收者，包括将土壤碳转化为气体，如甲烷（CH 4）。这一转换至关重要，因为甲烷是第二大温室气体，在过去40年中在大气中的浓度一直在上升。不幸的是，北极土壤的甲烷释放率似乎在增加，这一点很重要，因为北极过程造成了大气中25%以上的甲烷。因此，迫切需要了解和量化影响北极CH 4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，我们量化了2010年斯瓦尔巴群岛Ny-Alesund附近13个不同高北极地区的CH 4通量，并测量了近地表土壤中的58个地球化学和生物学参数（工作重点是厌氧-好氧界面）。然而，统计分析显示，关键的近地表微生物群体之间的相关性很弱（即，消耗甲烷的甲烷氧化菌和产生甲烷的甲烷菌）、地球化学条件和检测到的CH 4通量。事实上，数据表明，土壤剖面更深处的现象，包括深层甲烷生成以及融化的永冻层释放的气体和碳，可能比以前认为的对北极土壤的甲烷净释放更为重要。我们现在假设，如生物活性区（BAZ）以上的永久冻土的深度的因素;非生物永久冻土的贡献;和厌氧与好氧土壤层的比例厚度可能占主导地位观察到的CH 4释放速率。具体而言，如果BAZ较深，厌氧层相对于好氧层较厚，CH 4的产生将超过CH 4的消耗，导致CH 4向大气的通量升高。在这个项目中，我们将通过以下活动来测试这个备择假设：1。在2012年夏末返回纽约州-埃克塞特，在具有已知和对比CH 4通量的特定地点取芯进入BAZ和BAZ以下。在这些核心，我们将量化绝对产甲烷菌和甲烷氧化菌丰度与深度在每个站点;确定相关的地球化学条件，甲烷和氧气配置文件，永冻层深度，永冻层甲烷和碳含量;并测量甲烷通量，以关联土壤和永冻层条件与甲烷释放到大气中在每个站点; 2。统计比较每个站点CH 4平衡的估计生物与非生物贡献者，包括永久冻土CH 4和与融化相关的碳释放的影响; 3.通过测量从核心站点辐射出去的邻近站点的CH 4通量，将当地CH 4通量估计扩展到纽约州周围的景观水平，以更准确地估计不同类型景观对区域CH 4通量的相对贡献;与美国研究人员保持成功的国际合作，研究北极甲烷氧化菌-产甲烷菌的关系，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10天将在位于纽约州的NERC北极研究站进行。工作将在夏末进行，这是最大的永久冻土融化期，也是NERC现场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资助机构的更大提案。

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.