Abstract. The behavior of tundra ecosystems is critical in the global carbon cycle due to their wet soils and large stores of carbon. Recently, cooperation was observed between methanotrophic bacteria and submerged Sphagnum, which reduces methane emissions in this type of vegetation and supplies CO2 for photosynthesis to the plant. Although proven in the lab, the differences that exist in methane emissions from inundated vegetation types with or without Sphagnum have not been linked to these bacteria before. To further investigate the importance of these bacteria, chamber flux measurements, microbial analysis and flux modeling were used to show that methane emissions in a submerged Sphagnum/sedge vegetation type were 50% lower compared to an inundated sedge vegetation without Sphagnum. From examining the results of the measurements, incubation experiments and flux modeling, it was found that it is likely that this difference is due to, for a large part, oxidation of methane below the water table by these endophytic bacteria. This result is important when upscaled spatially since oxidation by these bacteria plays a large role in 15% of the net methane emissions, while at the same time they promote photosynthesis of Sphagnum, and thus carbon storage. Future changes in the spread of submerged Sphagnum, in combination with the response of these bacteria to a warmer climate, could be an important factor in predicting future greenhouse gas exchange from tundra.
Uncertainty analysis of eddy covariance CO<sub>2</sub> flux measurements for different EC tower distances using an extended two-tower approach