低温湿地甲烷古菌及其介导的甲烷产生途径

甲烷是重要的温室气体,低温湿地是大气甲烷的重要来源,因为湿地土壤中生活着大量的微生物包括甲烷古菌,它们将有机物降解转化为甲烷.本文总结了近年来低温湿地甲烷古菌群落组成、甲烷产生途径及其与环境的关系.研究显示,乙酸是低温湿地中主要的产甲烷物质,氢产甲烷过程主要发生在中温地区或酸性泥炭土中,而在盐碱水域中甲醇、甲胺是甲烷的重要底物.位于我国青藏高原的若尔盖湿地具有高海拔但低纬度的地理特征,我们的前期研究却显示甲醇在该湿地的甲烷排放中具有重要贡献.相应地,低温湿地中的甲烷古菌主要是利用甲基类化合物/乙酸的甲烷八叠球菌目和氢营养型的甲烷微球菌目.然而不同类型湿地甲烷排放途径及甲烷古菌的差异主要与环境的土壤类型、pH及植被类型相关,如刚毛荸荠生长的若尔盖湿地土壤中来源于甲醇的甲烷占全部甲烷的l7％；而木里苔草土壤中乙酸是产甲烷的主要前体物质.尽管已知冷适应的甲烷古菌在低温湿地的甲烷排放中发挥重要作用,但目前获得培养的嗜冷甲烷古菌却很少.冷响应的组学研究显示甲烷古菌的冷适应涉及到全局性生物学过程.

Methanogenic archaea and their mediated methanogenic pathways in cold wetland

Cold wetlands contribute great portion of the global methane. This is attributed to the inhabited diverse microbes including methanogenic archaea, where they convert the organic materials to methane. This review summarized the recent studies on the diversity of methanogenic archaea, and methane emission pathways in the cold wetlands and their correlation with environmental parameters. The so-far studies indicated that acetate is the main methanogenic precursor in the wetlands located in cold regions, hydrogenothophic methanogenesis occurs mainly in wetlands located in the warm regions and acidic peat, while methanol- and methyl amine-derived methanogensis restricts in ocean and saline water. Zoige wetland situates on Qinghai-Tibet Plateau locating in the low latitude region but at high altitude. Our previous study indicated the significant methanogenic contribution of methanol in this wetland. Accordingly, the methylotrophic and aceticlastic Methanosarcinales and hydrogenotrphic Methanomicrobiales constitute the predominant wetland archaeal community. However, methanogenic pathways and methanogen community structures vary with the wetland soil types and their pH as well as the vegetations, like methanol-derived methane accounting for 17% total methane flux in Eleocharis valleculosa growing soil, while acetate contribute the main methane in Carex muliensis planted soil in Zoige wetland. Though playing an important role in methane emission of cold wetlands, the so-far cultured cold-adaptive methanogenic strains are very few. The low-temperature-responsive genomics analyses show that a global gene reperpoire may involve in cold adaptation in methanogenic archaea.