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

摘要

Plant-mediated methane (CH_4) 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. 14C-pulse labeling of mesocosms with shoots isolated from entire belowground peat under controlled conditions allowed estimation of plant-mediated CH_4 flux and contribution of recent (~(14)C) photosynthates to total CH_4. The results showed (i) CH_4 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 CH_4 flux accounted for 38, 31 and 51 % of total CH_4 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 ~(14)C. Thus, microsites with S. palustris were char-acterized 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 photosyn-thates 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 ~(14)CH_4 as compared to larger E. vagina-turn. 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 C1-14production, consumption and transport and the attribution of those species to topographic forms of microrelief.