Dispersing Microbial Communities Increases Variability in Methane Fluxes in Arctic Sweden

The Arctic is warming at more than twice the rate seen globally, and formerly intact permafrost is thawing. As permafrost thaws, soil carbon that was previously unavailable becomes available to methanogenesis. Predicting the rate of this process can be challenging in part due to complex community assembly processes shaping microbial communities. Stordalen Mire, Sweden is a permafrost-dominated wetland where thaw is accompanied by hydrologic change, leading to wetter conditions in thawed habitats. This hydrologic change creates an anoxic environment, allowing for methanogenesis to occur, as well as potentially affecting the dispersal of methanogens between thawed habitats. To understand the release of methane (CH4) in this hydrologically-dispersed microbial community, we established a dispersal experiment in which we observed microbial communities that were able to disperse via water into a sand filled microcosm. During this experiment we took eight flux measurements over four weeks in Stordalen Mire to compare CH4 flux from the natural community to the hydrologically-dispersed community. The first four measurements were taken by placing semi-permanent collars in three habitats across a hydrologic and thaw gradient found in the Mire; palsa (intact permafrost), bog (hydrologically isolated, intermediate thaw), and fen (hydrologically connected, fully thawed). The second set of four measurements were taken after the collar locations had been cored and filled with sand. We measured the change in CH4 flux before and after the sand treatment to understand how the hydrologically dispersed microbial community contributed to CH4 released. We found that the palsa microbiome released minimal CH4 both before and after sand has been introduced to the experiment, fen has no significant change in CH4, and bog had a significant downward trend in CH4 uptake post-sand. Microbial communities were sampled pre- and post-sand from the three habitats and were characterized via DNA sequencing. This data, paired with the CH4 flux data, gives insight into the effect of microbial dispersal on CH4 release in thawing permafrost. More broadly, this experiment helps characterize the uncertainty in CH4 flux introduced by microbial dispersal processes which challenge our ability to predict carbon release from the Arctic.