Abstract Northern peatland methane (CH4) budgets are important for global CH4 emissions. This study aims to determine the ecosystem CH4 budget and
specifically to quantify the importance of Phalaris arundinacea by using different chamber techniques in a temperate wetland. Annually, roughly 70±35% of
ecosystem CH4 emissions were plant-mediated, but data show no evidence of significant diurnal variations related to convective gas flow regardless of
season or plant growth stages. Therefore, despite a high percentage of arenchyma, P. arundinacea-mediated CH4 transport is interpreted to be predominantly passive. Thus, diurnal variations are less important in
contrast to wetland vascular plants facilitating convective gas flow. Despite of plant-dominant CH4 transport, net CH4 fluxes were low (–0.005–0.016 µmol m-2 s-1) and annually less than 1% of the annual C-CO2 assimilation. This is considered a result of an effective root zone oxygenation resulting in increased CH4 oxidation in the rhizosphere at high water levels. This study shows that although CH4, having a global warming potential 25 times greater than CO2, is
emitted from this P. arundinacea wetland, less than 9% of the C sequestered counterbalances the CH4 emissions to the atmosphere. It is concluded that P.
arundinacea-dominant wetlands are an attractive C-sequestration ecosystem.