G3: Plants and microorganisms as drivers of CH4 production and exchange in coastal fens
supervised by Jurasinski, Liebner, Koebsch, Rehder
Within this topic we want to assess the influence of variation in salinity and sulfate concentrations in space and time on the composition and activity of the micro-organismic community as well as on substrate supply, methane production and emission through the vegetation. We expect the microbial community composition to vary with site geochemistry, and being reflected in the methane emission patterns.
State of the art
In the last 30 years, over 30,000 hectares of fens have been rewetted in Germany to restore their ecological functioning and mitigate carbon dioxide emissions. Post-rewetting methane emissions, however, are often extremely high in minerotrophic fens. Although this methane is produced almost entirely by microbes, only few studies examine microbial community structure and function in these systems. Data are especially sparse in temperate rich fens and even more so if they are coastal.
We have shown that, in contrast to what is known about marshes, methane emissions from coastal fens may be high even when sulfate is abundant (Koebsch et al. 2015, Hahn et al. 2015). During the first cohort we found that at our main field site, nature reserve „Heiligensee und Hütelmoor“, geochemistry influences the microbial community composition with depth and across the landscape. Our analysis of repeated pore water sampling showed that high sulfate concentrations and high methane concentrations from surface to pore waters were spatially separated suggesting sulfate reduction and methanogenesis to happen in different depth zones and, thus, supporting the hypothesis that episodic flooding with seawater generates strong legacy effects in the biogeochemical cycling on land (Jurasinski et al. 2018). The development of a shallow methanogenesis zone above a zone of intense sulfur cycling may be a specific feature of episodically flooded coastal wetlands, especially when hydrological changes cause freshening of surface waters (Koebsch et al. 2019). In addition, we found a low abundance of methanotrophs and a high abundance of methanogens, represented in particular by Methanosaetaceae (Wen & Unger et al. 2018). This highlights the need for a more differentiated perspective on coastal ecosystems as commonly neglected methane sources. Not only methane production but also emission pathways are important for the realised methane emissions. Although the contribution of plants to the realised emissions is well investigated in peat bogs and fens, knowledge about the connection between root exudates, inhibition of methanogenesis by high sulfate concentration, and the role of microbial community composition and activity patterns on methane production and emissions is missing.
Using a combination of GHG measurements, pore water sampling and peat coring with subsequent analysis of microbial community and chemical parameters in different coastal peatlands we want to further our understanding of the role of the plant and microbial communities for methane emissions from these systems. Starting from the 2nd cohort we widen our approach and include two new sites in the field monitoring. This allows us to address variation along gradients of flooding intensity and salinity.
Koebsch F, Winkel M, Liebner S, Liu B, Westphal J, Schmiedinger I, Spitzy A, Gehre M, Jurasinski G, Köhler S, Unger V, Koch M, Sachs T, Böttcher ME (2019) Sulfate deprivation triggers high methane production in a disturbed and rewetted coastal peatland. Biogeosciences 16:1937–1953
Wen X, Unger V, Jurasinski G, Koebsch F, Horn F, Rehder G, Sachs T, Zak D, Lischeid G, Knorr K-H, Böttcher M, Winkel M, Bodelier PLE, Liebner S (2018) Predominance of methanogens over methanotrophs in rewetted fens characterized by high methane emissions. Biogeosciences 15:6519-6536
Jurasinski G, Janssen M, Voss M, Böttcher ME, Brede M, Burchard H, Forster S, Gosch L, Gräwe U, Gründling-Pfaff S, Haider F, Ibenthal M, Karow N, Karsten U, Kreuzburg M, Lange X, Leinweber P, Massmann G, Ptak T, Rezanezhad F, Rehder G, Romoth K, Schade H, Schubert H, Schulz-Vogt HN, Sokolova I, Strehse R, Unger V, Westphal J, Lennartz B (2018) Understanding the Coastal Ecocline: Assessing Sea-Land Interactions at Non-Tidal, Low-Lying Coasts through Interdisciplinary Research. frontiers in Marine Science doi: 10.3389/fmars.2018.00342
Hahn J, Glatzel S, Köhler S, Jurasinski G (2015) Greenhouse gas exchange in a coastal fen in the first year after flooding - a systems shift. PLOSone 10:e0140657
Koebsch F, Jurasinski G, Koch M, Hofmann J, Glatzel S (2015) Controls for multi-scale temporal variation in ecosystem methane exchange during the growing season of a permanently inundated fen. Agricultural and Forest Meteorology 204:94–105