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Abstract:
The Tibetan plateau is a cold environment at high altitude and is very sensitive to global climate change. Wetlands on this plateau are among the major sources of the important greenhouse gas methane, and temperature is an important factor in controlling CH4 production. However, it remains unknown how CH4 production and microbial processes in such wetlands respond to climate warming. Therefore, we anaerobically incubated soil slurries at 10, 20, 30 and 45 degrees C for 100 days to investigate the effects of temperature on CH4 production and microbial community structure in the wetland soil next to NamCo, an alkaline lake on the Tibetan plateau. Rates and pathways of CH4 production were determined by measuring accumulation of CH4 and stable isotope fractionation, respectively. The microbial community structures were investigated by Illumina sequencing of bacterial and archaeal 16S rRNA and methanogenic mcrA genes and/or transcripts. Increasing the temperature from 10 to 30 degrees C enhanced CH4 production, but at 45 degrees C it almost ceased and the methanogenic precursor acetate accumulated. At lower temperatures, acetate accumulated only if acetoclastic CH4 production was inhibited with methyl fluoride. The abundance of bacterial and archaeal 16S rRNA genes and mcrA genes were generally around 10(8) g(-1) dry weight soil or higher. Aaproteobacteria became increasingly abundant with time of incubation (up to 100 days) and temperature increasing from 10 to 30 degrees C. At 45 degrees C, however, Firmicutes became the dominant bacterial phylum. While about > 70% of CH4 was produced from acetoclastic methanogenesis at 10-30 degrees C, hydrogenotrophic methanogenesis was the dominant ( > 82%) pathway at 45 degrees C. The acetoclastic genus Methanoseata was the main methanogen at low (10 degrees C) and moderate (20 degrees C and 30 degrees C) temperatures, but the hydrogenotrophic genera Methanoregula and Methanomassiliicoccus dominated at high temperature (45 degrees C). Bathyarchaeota, with unknown function, dominated next to methanogenic Euryarchaeota the archaeal community, especially on DNA level. The methanogenic archaeal community composition of NamCo soil resembled that of alkaline lake sediments from the Tibetan Plateau. Structure and function of the methanogenic microbial community in alkaline wetlands and their temperature response seem to be different from those found in neutral paddy soil or acidic peatland soil.
