The influence of Carex aquatilis and Juncus balticus on methane dynamics: A comparison with water sourced from a natural and a constructed fen

•Constructed fen water limits CH4 emissions and pore water concentration.•Carex aquatilis may increase labile carbon root exudates in peat.•Juncus balticus may increase oxygen transport to the root zone (radial oxygen loss).•Higher CH4 concentration and potential production found from C. aquatilis columns.