Stable Carbon composition of Methane in Eurasian Peatlands: CH4 production, transport and oxidation
Final Report Abstract
Understanding key mechanisms of the methane (CH4) turnover in terrestrial ecosystems and specifically in boreal peatlands as one of the largest pools of CH4 globally, is one of the critical tasks for broad scientific community. Methane together with CO2 are two most potent greenhouse gases which increase in the atmosphere trigger the climate change. The current project attempted to fill the existing knowledge gaps and using the stable C isotope signature in both gases as a tool, to identify the processes of CH4 production, transport and oxidation. Evidence obtained from field studies and set of laboratory incubation experiments demonstrated the conservative conditions of the deepest peat layers (below 0.5 m), where methanogenesis occurred predominantly through hydrogenotrophic (CO2-reduction) pathway as revealed through the most depleted 13C-CH4 and most enriched 13C-CO2 signatures. In contrast, the top peat layers (0.2-0.5 m) were the dynamical environment where the isotope signatures of gases were affected by number of processes. Here, a peatland’s microtopographical units – elevated and less moist hummocks, depressed and wet hollows, and intermediate lawns – had the most pronounced effects on CH4 and CO2 dynamics mainly through the dominated vascular plant communities and the position of water table. As a result, the identification of acetoclastic pathway of methanogenesis which supposed to dominate in top peat layers with the highest availability of recent plant-derived deposits was hindered mainly by the processes of CH4 oxidation, whereas diffusion and plant-mediated transport appeared to have lesser effect on δ13C of CH4 and CO2. Interestingly, the commonly applied concept of the high CH4 oxidation potential of the hummocks’ topsoil was disproved in one of the incubation experiments, where neither mass-based oxidation nor the incorporation of new 13C-CH4 to the total organic matter, nor its ratio to microbial biomass carbon revealed the pronounced CH4 oxidation at 0.2 m depth of hummocks. Furthermore, 0.5 m was found as the optimal depth below hummocks and lawns for living and activity of microorganisms as depicted by the profiles of DNA-extracted microbial biomass and catalytic efficiency of key extracellular enzymes. Distribution and activity of microorganisms in peat profile was best correlated with the soil P content highlighting this nutrient, and to the lesser extend N or S, as an important regulating factor for C turnover in boreal peatlands. Surprisingly, the observed changes of δ13C-CH4 and δ13C-CO2 signatures at the deepest anaerobic peat horizons (0.5-2.0 m) followed the CH4 oxidative pattern after the top aerobic layers (0.2-0.5 m). This finding gave the first ideas to consider a phenomenon of so-called anaerobic methane oxidation. Based on the preliminary information from an incubation experiment where anaerobic methane oxidation was quantitatively measured, a new DFG Individual Grant Program was successfully applied. The upcoming research is going to answer the main questions, whether the process of anaerobic methane oxidation is ecologically relevant for the terrestrial ecosystems (natural and re-established peatlands and rice paddies) and which main mechanisms are involved.
Publications
- (2015). Evidence on Anaerobic Methane Oxidation (AOM) in a boreal cultivated peatland with natural and added electron acceptors. Geophysical Research Abstracts 17, EGU2015-11003-1
Dorodnikov, M., Silvennoinen, H., Martikainen, P., Dörsch, P.
- (2016). Effects of nitrate and sulfate on greenhouse gas emission potentials from microform derived peats of a boreal peatland: A 13C tracer study. Soil Biology and Biochemistry, 100, 182-191
Lozanovska, I., Kuzyakov, Y., Krohn, J., Parvin, S., Dorodnikov, M.
(See online at https://doi.org/10.1016/j.soilbio.2016.06.018) - Microform-related belowground CH4 concentrations and stable carbon isotope signatures as proxies for determination of CH4 turnover processes in a boreal peatland. In: “Ecosystem of a Mesooligotrophic Peatland in Northwestern Russia: development, structure, and function”, eds. S. Zagirova and J. Shneider, Chapter 12, S. 121-131. Syktyvkar, Russia, 2016. ISBN 978-5-89606-562-3
Dorodnikov, M, Knoblauch, C., Zagirova, S., Sivkov, M., Wilmking M.
- Microtopography matters for CH 4 formation in a peat soil: a combined inhibitor and 13C study
Krohn, J., Lozanovska, I., Kuzyakov Y., Dorodnikov, M.
(See online at https://dx.doi.org/10.5194/bg-2016-162-RC2)
