Plant community composition explains spatial variation in year-round methane fluxes in a boreal rich fen

Abstract. Climate change is expected to impact the methane (CH4) budget of boreal peatlands, highlighting the need to understand the factors that influence methane cycling, including plant community structure. In northern peatlands, the majority of methane is transported through plants, and the magnitude of this process is strongly linked to plant community composition. Therefore, detailed information about the role of plants in regulating year-round methane fluxes is highly valuable. This paper explores the causes of spatial variability in plot-scale methane fluxes in a northern boreal rich fen. Methane fluxes were measured using the manual chamber technique in the context of fine-scale biomass variations in plant community composition from 36 study plots over 232 d throughout a full year. The mean methane flux rates for snow-free and snow seasons were 2.55 and 0.21 mg CH4 m−2 h−1, respectively. We found a significant correlation between methane fluxes and a plant community type associated with the presence of sedge Carex rostrata during three studied periods: year-round, snow-free, and snow season. C. rostrata was present at 13 out of 36 plots, and these 13 plots contributed 44 %–49 % of the total measured methane fluxes. The biomass of vascular plants, sedges, and C. rostrata, as well as the ratio of vascular plant to bryophyte biomass, was also significantly correlated with methane fluxes in year-round and snow-free seasons. By identifying vegetation-driven emission hotspots, these results can enhance efforts to upscale emission predictions and improve ecosystem-scale methane modeling. Thus, our findings provide valuable insights for predicting realistic future changes in peatland methane emissions throughout the year.