Methanogenic Pathways in Pürgschachen Moor

Microbially mediated methanogenesis is a considerable source of methane (CH4) and has a major role in the global carbon cycle. In peatlands, acetate, CO2 and methylated compounds are precursors for CH4 and different substrates are used by different microorganisms. CH4 may be produced by a) acetate disproportionation (acetoclastic/acetotrophic methanogenesis), b) reduction of carbon dioxide by dihydrogen (hydrogenotrophic methanogenesis), and c) using methylated compounds (methylotrophic methanogenesis). As different methane sources have different carbon isotopic ratios, those signatures may be used to divide emissions from different sources, although these can vary temporally and spatially. Here, we hypothesize that CH4 production pathways from Sphagnum peat with clipped vascular vegetation (Callluna Vulgaris) significantly differs from CH4 production pathways from peat cores with vascular plant cover.

In order to test this hypothesis, six undisturbed peat mesocosms from Pürgschachen Moor were sampled to determine the CO2 and CH4 efflux and its 12C/13C signature for four weeks. Three control cores were left unclipped as control and in three cores, vascular vegetation was clipped to assess the significance of vascular vegetation to CH4 emissions. Ancillary parameters examined were dissolved organic carbon and acetate concentrations in peat pore water as well as hot water soluble carbon from peat.

CO2 fluxes ranged in clipped cores between 2.4 to 12.2 g m-2 h-1 and in control cores between 4.13 to 14.6 g m-2 h-1. CH4 fluxes ranged from 0.058 to 0.16 g m2 h-1 in the clipped cores and from 0.046 to 0.751 g m2 h-1 in the control group. For both CO2 and CH4, treatment had a significant effect on the fluxes.  δ13C for CH4 values in the experiment group (-55.6 ± 2.45‰) were in the same range as the control group, whereas after the clipping the experiment group values slightly decreased to -54.1 ± 2.65‰. For the control group, δ13C values were -55 ± 2.2‰. δ13CO2 was -11.2 ± 0.72‰ before and -10.8 ± 0.67‰ after clipping in the experiment group. In the control group, the average was -11.2 ± 0.71‰.

Taking into consideration the aforementioned results and other parameters measured throughout this study, it can be acclaimed that the presence of vascular vegetation changes the ability of the peat profile to produce and emit both CO2 and CH4. Even though no significant difference found between the control and the experiment group for δ13CH4, it can be acclaimed that in Pürgschachen Moor the hydrogenotrophic pathway is dominant, with average δ13CH4 values of -55 ± 2 ‰, although both pathways coexist.