陆地生态系统甲烷产生和氧化过程的微生物机理

陆地生态系统存在许多常年性或季节性缺氧环境,如:湿地、水稻土、湖泊沉积物、动物瘤胃、垃圾填埋场和厌氧生物反应器等。每年有大量有机物质进入这些环境,在缺氧条件下发生厌氧分解。甲烷是有机质厌氧分解的最终产物。产生的甲烷气体可通过缺氧-有氧界面释放到大气,产生温室效应,是重要的温室气体。产甲烷过程是缺氧环境中有机质分解的核心环节,而甲烷氧化是缺氧-有氧界面的重要微生物过程。甲烷的产生和氧化过程共同调控大气甲烷浓度,是全球碳循环不可分割的组成部分。对陆地生态系统甲烷产生和氧化过程的微生物机理研究进展进行了概要回顾和综述。主要内容包括:新型产甲烷古菌即第六和第七目产甲烷古菌和嗜冷嗜酸产甲烷古菌的发现;短链脂肪酸中间产物互营氧化过程与直接种间电子传递机制;新型甲烷氧化菌包括厌氧甲烷氧化菌和疣微菌属好氧甲烷氧化菌的发现;甲烷氧化菌生理生态与环境适应的新机制。这些研究进展显著拓展了人们对陆地生态系统甲烷产生和氧化机理的认识和理解。随着新一代土壤微生物研究技术的发展与应用,甲烷产生和氧化微生物研究领域将面临更多机遇和挑战,对未来发展趋势做了展望。

Microbial mechanisms of methane production and oxidation in terrestrial ecosystems

Terrestrial ecosystems consist of oxic and anoxic environments. Anoxic environments can be permanent or temporary, and they include natural wetlands, paddy field soils, lake and river sediments, rumens, landfills, and anaerobic bioreactors. Large amounts of organic matter are released into these environments annually. Under anoxic conditions, organic matter is decomposed anaerobically, with methane (CH₄) as the final product. CH₄ can diffuse through the anoxic-oxic interface and enter the atmosphere, and can become a potent greenhouse gas. Methanogenesis appears to be the core process of organic matter decomposition in anoxic environments. Methane oxidation takes place actively in the anoxic-oxic interface through which CH₄ diffuses. Microbial production and oxidation of CH₄ in terrestrial ecosystems together regulate the atmospheric concentration of CH₄ and contribute to a crucial part of global carbon cycling. In this review, we report the recent advances in the mechanistic understanding of microbial CH₄ production and oxidation in terrestrial ecosystems. The major topics include: discovery of novel methanogens, particularly of the psychrophilic and acidophilic methanogens, and the 6^th and 7^th orders of methanogens; syntrophic interaction and direct interspecies electron transfer in the methanogenic oxidation of short-chain fatty acids; the discovery of novel methanotrophs, including anaerobic and aerobic verrucomicrobial methanotrophs; and the novel ecophysiological properties of methanotrophs. These advances have greatly increased our understanding of microbial CH₄ production and oxidation in terrestrial ecosystems, and with the development of new methods and technologies, more breakthroughs are expected. We also propose a few perspectives for future studies.