δ13CPLFA Analysis of the Microbial Community Composition within Peat Depth Profiles in Response to Deep Peat Warming and Environmental Conditions

Abstract

Peatlands represent a critical and unique natural resource, especially in their role as carbon sinks. As much of the world’s peatlands are located in Northern ecosystems where the climate is changing at a rapid pace, there is great interest and concern with how the changing climate will influence them. The microbial community is a crucial aspect of the peatland ecosystem in terms of mediating biogeochemical cycling. 13CPLFA analysis was used to characterize the microbial community and provide isotopic information about microbial carbon use through peat depth profiles taken from the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) Project; an extensive study of the response of peatlands to climatic manipulation in the Marcell Experimental Forest in northern Minnesota. This analysis took place just before, and during, deep peat warming (at 2 meters) with temperature treatments (+0.0, +2.25, +4.5, +6.75, +9.0). Pre-warming sampling occurred in June 2014, with warming stabilizing around September 2014. These sampling dates were used to characterize the microbial community. The June 2015 sampling date was used to determine if the microbial community and carbon use responded to the deep peat warming. Strong vertical stratification indicates that depth is the biggest determining factor in natural peatlands on the microbial community composition and carbon use. There was also considerable natural variation of the microbial community over time, which will prove challenging in determining treatment effects. The surface of the peat profile had the most change over time, and had the strongest correlation with environmental variables, suggesting that the microbial community in the surface of the peat profile is more responsive to external conditions than deeper peat. The analysis of microbial communities before treatment initiation revealed that there were significant relationships of the microbial community with temperature, mostly related to depth under natural conditions. The deep peat warming enhanced that existing sensitivity. The fungal community in particular responded to the warming treatment, with increased relative abundance and use of newer carbon under higher temperatures. Decreased anaerobic bacterial relative abundance and actinomycete abundance in the top 20cm in response to warming indicates a microbial community shift towards fungal abundance, especially in the surface of the peat profile. In summary, fungal communities, and surface microbial communities in general could be the main drivers of change in peatlands under warming. This will have an especially big impact on nutrient cycling within the peatland ecosystem.