Abstract. Contribution of recent photosynthates to methanogenesis and plant-mediated methane (CH4) transport were studied on two dominating vascular plant species – Eriophorum vaginatum and Scheuchzeria palustris – at three microform types (hummocks, lawns and hollows) of a boreal natural minerogenic, oligotrophic fen in Eastern Finland. Measurements of total CH4 flux, isolation of shoots from entire peat and 14C-pulse labeling of mesocosms under controlled conditions allowed estimation of plant-mediated CH4 flux and contribution of recent (14C) photosynthates to total CH4. The obtained results showed (i) CH4 flux increases in the order E. hummocks ≤ E. lawns < S. hollows corresponding to the increasing water table level of the microforms as derived from in situ measurements. (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 14C. Thus, S. palustris microsites are characterized by a higher efficiency for transporting CH4 from the peat column to the atmosphere when compared to E. vaginatum of drier lawns and hummocks. Contribution of recent plant photosynthates to methanogenesis was not depended on the amount of plant biomass: smaller S. palustris had higher 14CH4 as compared to larger E. vaginatum. Therefore, for the assessment of CH4 production and emission over meso- and macroscales as well as for the implication and development of C modeling of CH4 fluxes, it is necessary to account for plant species-specific processes including CH4 production, consumption and transportation and the attribution of those species to topographic microforms.
Contribution of recent plant photosynthates of <i>Eriophorum vaginatum</i> and <i>Scheuchzeria palustris</i> to methanogenesis and CH<sub>4</sub> transport at a boreal mire: a <sup>14</sup>C pulse-labeling study