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Fears of global climate change and its potential outcomes have stimulated intensive efforts to update current climate models. Nevertheless, most of the existing models lack inputs specific to peatlands and/or to microorganisms. Peatlands store up to 30% of the world’s soil carbon and contribute up to 30% of atmospheric methane, thus their response to climate change is of special interest. Peatlands are mostly found at northern high latitudes where nutrient poor conditions foster Sphagnum as a keystone plant species. My studies focus on understanding the response of peatland ecosystems to climate change at the Marcell Experimental Forest (MEF) in northern Minnesota, USA. At MEF, the U.S. DOE has created a unique multi-faceted large scale climate manipulation experiment known as SPRUCE (Spruce and Peatland Response Under Climatic and Environmental Change), initiated in June 2014. From June 2014 to June 2015, we evaluated the responses of microbial communities, both in structure and metabolic potential, to 5 soil warming treatments (+0°C; +2.25°C; +4.5°C; +6.75°C; +9°C). Methane flux was correlated with temperature in the treatments, suggesting that increases in soil temperature apparently drive the emission response. However, multiple lines of evidence, including laboratory incubations, indicate that CH4 emission increased due to surface processes and not degradation of deep carbon. Characterization of in situ microbial communities indicated no significant effect of temperature or time on community composition or function. Specifically, the potential activity of extracellular lignin oxidative enzymes showed that one year of soil warming had a limited effect on microbial activity. While the physiology and ecology of Sphagnum have been well-studied, the structure, function and response of their microbiome to climate change is less understood. Sphagnum-associated, nitrogen-fixing bacteria are thought to play a major role in plant functioning and the peatland nitrogen cycle. Therefore, we conducted intensive sampling of the S. magellanicum phyllosphere-associated microbial communities. Our results revealed a significant geographical effect on general and nitrogen-fixing microbial communities. Interestingly, the nitrogen-fixing core-microbiome contained only 2 members, taxonomically affiliated with Nostoc azollae (symbiotic Cyanobacteria) and Methyloferula stellate (an obligate methanotroph). Potentially synergistic interactions between these nitrogen-fixing bacteria not only provide the plant with sufficient nitrogen, but may also reduce methane emission from peatlands. Our observations of evolutionary conserved nitrogen-fixing bacteria among representative peatland sites further knowledge of the benefits of the microbiome to Sphagnum host fitness and to ecosystem function.