CH4 and CO2 production below two contrasting peatland micro-relief forms: An inhibitor and delta C-13 study

Two peatland micro-relief forms (microforms) - hummocks and hollows - differ by their hydrological characteristics (water table level, i.e. oxic-anoxic conditions) and vegetation communities. We studied the CH4 and CO2 production potential and the localization of methanogenic pathways in both hummocks and hollows at depths of 15, 50, 100, 150 and 200 cm in a laboratory incubation experiment. For this purpose, we measured CH4 and CO2 production rates, peat elemental composition, as well as delta C-13 values of gases and solids; the specific inhibitor of methanogenesis BES (2-bromo-ethane sulfonate, 1 mM) was aimed to preferentially block the acetoclastic pathway. The cumulative CH4 production of all depths was almost one fold higher in hollows than in hummocks, with no differences in CO2. With depth, CO2 and CH4 production decreased, and the relative contribution of the hydrogenotrophic pathway of methanogenesis increased. The highest methanogenic activity among all depths and both microforms was measured at 15 cm of hollows (91%) at which the highest relative contribution of acetoclastic vs. hydrogenotrophic pathway (92 and 8%, respectively) was detected. For hummocks, the CH4 production was the highest at 50 cm (82%), where relative contribution of acetoclastic methanogenesis comprised 89%. The addition of 1 mM BES was not selective and inhibited both methanogenic pathways in the soil. Thus, BES was less efficient in partitioning the pathways compared with the delta C-13 signature. We conclude that the peat microforms - dry hummocks and wet hollows - play an important role for CH4 but not for CO2 production when the effects of living vegetation are excluded. (C) 2017 Elsevier B.V. All rights reserved.