| 29 Jan 2026
Plant belowground traits indicate increased plant-mediated methane transport along a peatland permafrost thaw gradient
Abstract. Permafrost thaw in subarctic peatlands alters ecosystem methane (CH4) fluxes. Collapsing permafrost palsas change hydrology, interstitial oxygen availability, and vegetation composition, and each of these factors contribute to net CH4 flux by influencing CH4 production, consumption and transport. However, changes in plant-mediated CH4 fluxes have mostly been estimated using aboveground characteristics, such as biomass and leaf area, leaving belowground parts (roots and rhizomes) understudied despite their direct contact to depth-dependent CH4 flux processes. Here, we explored the potential of using root and rhizome traits as proxies for plant-mediated CH4 cycling along a peatland permafrost thaw gradient in subarctic Sweden. We investigated changes in root and rhizome biomass, surface area (SA), diameter, tissue density (TD), and specific root length (SRL) along the permafrost thaw gradient, and how these traits relate to early-, middle-, peak- and season median CH4 fluxes. We utilized chamber CH4 flux and pore water CH4 concentration and isotopic measurements during the productive season. Shrub SRL, diameter and isotopic data suggested increased plant-mediated carbon substrates available for acetoclastic methanogenesis across the thaw gradient. Root TD, proxy for root porosity, decreased with thaw and had negative correlations with CH4 fluxes throughout the season. Simultaneously, herbaceous rhizome SA-CH4 flux correlations were positive and pore water CH4 concentrations were lowest in the fully thawed stage. These results indicated increasing herbaceous plant-mediated transport of acetoclastically-produced CH4 with thaw. Our study demonstrates that integrating plant belowground traits with environmental and biogeochemical data can help improve CH4 flux predictions in thawing landscapes and revealed key mechanistic insights regarding the interplay between substrate availability for methanogenesis and gas transport.
