Plant-mediated CH4 transport and contribution of photosynthates to methanogenesis at a boreal mire: a 14C pulse-labeling study

Plant-mediated methane (CH4) transport and the contribution of recent photosynthates to methanogenesis were studied on two dominating vascular plant species - Eriophorum vaginatum and Scheuchzeria palustris - at three types of microrelief forms (hummocks - E. hummocks, lawns - E. lawns and hollows - S. hollows) of a boreal natural minerogenic, oligotrophic fen in Eastern Finland. C-14-pulse labeling of mesocosms with shoots isolated from entire belowground peat under controlled conditions allowed estimation of plant-mediated CH4 flux and contribution of recent (C-14) photosynthates to total CH4. The results showed (i) CH4 flux increased in the order E. hummocks <= E. lawns < S. hollows corresponding to the increasing water table level at the relief microforms as adjusted to field conditions. (ii) Plant-mediated CH4 flux accounted for 38, 31 and 51% of total CH4 at E. hummocks, E. lawns and S. hollows, respectively. (iii) Contribution of recent photosynthates to methanogenesis accounted for 0.03% for E. hummocks, 0.06% for E. lawns and 0.13% for S. hollows of assimilated C-14. Thus, microsites with S. palustris were characterized by higher rates of transported CH4 from the peat column to the atmosphere when compared to E. vaginatum of drier lawns and hummocks. Contribution of recent photosynthates to methanogenesis was dependent on the plant biomass within-species level (E. vaginatum at hummocks and lawns) but was not observed between species: smaller S. palustris had higher flux of (CH4)-C-14 as compared to larger E. vaginatum. Therefore, for the assessment of CH4 dynamics over meso-and macroscale as well as for the implication and development of the modeling of CH4 fluxes, it is necessary to account for plant species-specific differences in CH4 production, consumption and transport and the attribution of those species to topographic forms of microrelief.