CH4 transport in wetland plants under controlled environmental conditions: untangling the impacts of phenology

O_LIMethane (CH4) fluxes at plant surfaces are the net result of transport of soil-produced CH4 and within-plant CH4 production and consumption, yet factors and processes controlling these fluxes remain unclear. C_LIO_LIWe conducted high-frequency automated CH4 flux measurements from shoots of Carex rostrata (sedge), Menyanthes trifoliata (forb) and shrubs (Betula nana, Salix lapponum) during early, high and late summer in a climate-controlled environment to assess the effects of environmental variables, seasonality and CH4 cycling microbes in the CH4 flux. Measurements were conducted from intact plant-soil samples collected throughout growing seasons 2020 and 2021 from Lompolojankkafen, northern Finland. C_LIO_LIAll studied species showed seasonal variability in CH4 fluxes. The CH4 fluxes were not impacted by light level, while out of the studied species, porewater CH4 concentration increased fluxes from all but B. nana. Air temperature only and negatively affected CH4 flux from C. rostrata. Both methanogens and methanotrophs were detected in aboveground parts of S. lapponum and M. trifoliata, methanotrophs in B. nana, while neither were detected in C. rostrata. C_LIO_LIOur study demonstrates that the seasonal phase of the plants regulates CH4 flux they mediate across species, which was not observed in the field. The detection of methanogens and methanotrophs in herbs and shrubs suggests that microbial processes may contribute to their CH4 flux. C_LI