CH4 transport in wetland plants under controlled environmental conditions – separating the impacts of phenology from environmental variables

Background and Aims Methane (CH 4 ) fluxes at peatland plant surfaces are net results of transport of soil-produced CH 4 and within-plant CH 4 production and consumption, yet factors and processes controlling these fluxes remain unclear. We aimed to assess the effects of seasonality, environmental variables, and CH 4 cycling microbes on CH 4 fluxes from characteristic fen species. Methods Four species ( Carex rostrata , Menyanthes trifoliata , Betula nana , Salix lapponum ) were selected, and their CH 4 fluxes determined in climate-controlled environments with three mesocosms per growing season per species. Microbial genes for CH 4 cycling were analysed to check the potential for within-plant CH 4 production and oxidation. Two extra experiments were conducted: removal of C. rostrata leaves to identify how leaves constrain CH 4 transport, and a labelling experiment with S. lapponum to distinguish between plant-produced and soil-produced CH 4 in the plant flux. Results All species showed seasonal variability in CH 4 fluxes. Higher porewater CH 4 concentration increased fluxes from C. rostrata and M. trifoliata , decreased fluxes from S. lapponum , and did not affect fluxes from B. nana . Air temperature only and negatively affected CH 4 flux from C. rostrata . Light level did not impact CH 4 fluxes. Both methanogens and methanotrophs were detected in shoots of S. lapponum and M. trifoliata , methanotrophs in B. nana , and neither in C. rostrata . Conclusion Our study demonstrates that the seasonal phase of the plants regulates the CH 4 fluxes they mediate across species. The detection of methanogens and methanotrophs in herbs and shrubs suggests that microbial processes may contribute to their CH 4 fluxes.