Radial oxygen loss by the cushion plant Eriocaulon schimperi prevents methane emissions from an East‐African mountain mire

Groundwater-fed fens are known sources of methane (CH₄ ) emissions to the atmosphere, and these are known to be mediated by the vegetation. In a fen located in the Bale Mountains, Ethiopia, we assessed the effects of a cushion plant (Eriocaulon schimperi) and a sedge (Carex monostachya) on rhizosphere biogeochemistry. Methane and CO₂ concentrations and pH were measured in pore-water at different depths in the profile. Redox potentials and NaCl-extractable element concentrations were analysed in soil samples from sites dominated by either E. schimperii or C. monostachya. Nutrient and element concentration were analysed in plant tissues. At Carex-dominated sites, CH₄ concentrations increased from 70 μmol·l⁻¹ at a depth of 10 cm to 130 μmol·l⁻¹ at a depth of 100 cm. CH₄ concentrations at Eriocaulon-dominated sites were almost zero (<1 μmol·l⁻¹ ) to a depth of 100 cm. Simultaneously, soil redox potentials and CO₂ concentrations were higher at Eriocaulon-dominated sites, indicating a low potential for CH₄ production and a high potential for CH₄ oxidation. Eriocaulon schimperi displayed a root investment strategy to cope with the harsh environment, similar to the cushion plant Astelia pumila in Patagonian bogs. This strategy is characterised by high root/shoot ratios, high root porosity and density under high redox conditions. Both cushion plant species create an aerobic rhizosphere through radial oxygen loss from deep roots, which strongly reduce CH₄ fluxes to the atmosphere.