Methane oxidation associated with submerged brown mosses reduces methane emissions from Siberian polygonal tundra

Summary 1.  Methane (CH 4 ) oxidation (methanotrophy) associated with submerged brown moss species occurs in polygonal tundra environments of the Siberian Arctic. Methanotrophic bacteria living in close association with mosses are thus not restricted to Sphagnum species and low‐pH peatlands. 2.  Moss‐associated methane oxidation (MAMO) can be an effective buffer for CH 4 emissions from permafrost‐affected tundra, a region that is of high importance for the global greenhouse gas budget. Combining biogeochemical and molecular approaches revealed that MAMO in polygonal ponds exceeds methanotrophic activity in terrestrial sites by up to two orders of magnitude. 3.  Moss‐associated methane oxidation is not only promoted by submerged conditions but also by light exposure. Polygonal ponds covered by the brown moss Scorpidium scorpioides became a net sink for atmospheric CH 4 (−1.7 mg CH 4  m −2  day −1 ) when exposed to sunlight but a CH 4 source (21.6 mg CH 4  m −2  day −1 ) in the absence of light. 4.  Based on stable isotope probing with 13 CH 4 , carbon deriving from CH 4 was incorporated into the bacterial fatty acids 16:1ω7 and 18:1ω9/ω7 common in methanotrophs and into plant phytol, sitosterol and stigmastanol, all of which are highly abundant in moss biomass. 5.   Synthesis . A mutualistic symbiosis between methanotrophic bacteria and brown mosses reduces CH 4 emissions from Arctic polygonal tundra by at least 5%. Both partners benefit from this association: the moss from the additional CO 2 supplied through methane oxidation and the methane‐oxidizing bacteria from the oxygen produced through photosynthesis. Considering that submerged mosses are widely abundant in the polar region, MAMO may have a major impact on carbon turnover rates in Arctic freshwater environments.