Anaerobic Oxidation of Methane in Terrestrial Ecosystems (AOMTE): mechanisms and ecological relevance

甲烷厌氧氧化（AOM）是在缺氧条件下与各种终端电子受体（除氧外），如硫酸盐、硝酸盐、亚硝酸盐、某些金属（铁、锰）或有机化合物消耗甲烷（CH4）的微生物过程。AOM在海洋生态系统中很常见，微生物硫酸盐还原消耗了沉积物中产生的大部分CH4。尽管AOM具有全球意义，但其机制（特定电子受体、微生物群等）、最佳条件和AOM在陆地生态系统中的相关性几乎是未知的。因此，迫切需要对陆地生态系统中的AOM进行研究，特别是那些暴露于长期厌氧条件下的生态系统，如自然或恢复的泥炭地和稻田。本文主要研究了在大气候梯度条件下四个研究点（瑞典的一个天然泥炭地、德国的两个恢复泥炭地和中国的一个稻田）的AOM机制和强度。为了估计原位AOM率，将使用地下13C-CH4标记。AOM的产物（释放13CO2）与孔隙水电子受体的动力学将允许评估AOM强度并将其与每个地点的现有环境条件联系起来。在实地研究的同时，我们还将对所有研究地点的土壤进行一系列实验室实验，深入研究AOM的具体机制和微生物群。在计划的微观实验中，最常见的电子受体的一个广泛的浓度范围将与13C-CH4一起添加。应用新的电化学分析方法（测量电子受体的电子交换能力），在13CH4氧化产生的13CO2和PLFA和GDGT生物标志物（细菌和古菌群落的代理）中追踪13C，将揭示最高潜在AOM率的最佳条件，并确定负责AOM的微生物群。据我们所知，目前的建议是第一次尝试估计原位AOM率，并确定在欧亚大陆持续产生CH4的一系列生态系统中负责的微生物群。最后，对AOM机制的理解可能会改变陆地生态系统中CH4循环的现有概念，并将改进当前基于过程的区域和全球碳平衡模型。

Anaerobic oxidation of methane (AOM) is a microbial process of methane (CH4) consumption under anoxic conditions with various terminal electron acceptors (other than oxygen), e.g. sulfate, nitrate, nitrite, some metals (Fe, Mn) or organic compounds. AOM is common in marine ecosystems, where microbial sulfate reduction consumes most of the CH4 produced in sediments. Despite the global significance of AOM, the mechanisms (specific electron acceptors, microbial groups, etc.), optimal conditions and AOM relevance in terrestrial ecosystems are almost unknown. Therefore, there is a strong need for investigation of AOM in terrestrial ecosystems, especially those exposed to prolonged anaerobic conditions such as natural or restored peatlands and rice paddies. This proposal focuses on the AOM mechanisms and intensity within a large climate gradient in four research sites: one natural peatland in Sweden, two restored peatlands in Germany and one rice paddy field in China. To estimate the in situ AOM rate, the belowground 13C-CH4 labeling will be applied. The product of AOM (released 13CO2) together with the dynamics of porewater electron acceptors will allow to assess the AOM intensity and link it to existing environmental conditions at each of the sites. Along with the field studies, the specific mechanisms and the microbial groups driving AOM will be thoroughly investigated in a set of laboratory experiments with the soils from all research sites. In planned microcosms experiments, a broad concentration range of the most common electron acceptors will be added together with 13C-CH4. Application of novel methods of electrochemical analysis (measurement of electron exchange capacities of the electron acceptors), 13C tracing in 13CO2 produced by 13CH4 oxidation and in PLFA and GDGT biomarkers (proxies for bacterial and archaeal communities) will reveal the optimal conditions for the highest potential AOM rates and determine microbial groups responsible for AOM. To our knowledge, the current proposal is the first attempt to estimate the in situ AOM rate and to determine the responsible microbial groups in a range of ecosystems with sustained CH4 production on Eurasian continent. Finally, understanding of AOM mechanisms may change the existing concept of CH4 cycling in terrestrial ecosystems and will improve current process-based models of regional and global carbon balance.