Effect of temperature on the microbial community responsible for methane production in alkaline NamCo wetland soil

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 CH 4 production. However, it remains unknown how CH 4 production and microbial processes in such wetlands respond to climate warming. Therefore, we anaerobically incubated soil slurries at 10, 20, 30 and 45 °C for 100 days to investigate the effects of temperature on CH 4 production and microbial community structure in the wetland soil next to NamCo, an alkaline lake on the Tibetan plateau. Rates and pathways of CH 4 production were determined by measuring accumulation of CH 4 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 °C enhanced CH 4 production, but at 45 °C it almost ceased and the methanogenic precursor acetate accumulated. At lower temperatures, acetate accumulated only if acetoclastic CH 4 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. Alphaproteobacteria became increasingly abundant with time of incubation (up to 100 days) and temperature increasing from 10 to 30 °C. At 45 °C, however, Firmicutes became the dominant bacterial phylum. While about >70% of CH 4 was produced from acetoclastic methanogenesis at 10–30 °C, hydrogenotrophic methanogenesis was the dominant (>82%) pathway at 45 °C. The acetoclastic genus Methanoseata was the main methanogen at low (10 °C) and moderate (20 °C and 30 °C) temperatures, but the hydrogenotrophic genera Methanoregula and Methanomassiliicoccus dominated at high temperature (45 °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.