Elucidating the role of natural organic matter in the methane producing and consuming microbial processes in northern peatlands

• Applicant: Professor Dr. Andreas Kappler
• Subject Area: Soil Sciences
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530188224

Peatlands are the largest reservoirs of organic carbon on Earth. 80% of the global peatland area is in the northern hemisphere; thus, northern peatlands constitute the primary natural source of carbon-based greenhouse gases (GHGs), such as CH4 and CO2. CH4 is of particular relevance, given that it possesses ~28 times the potential to cause global warming compared to CO2. The amount of CH4 released by peatlands is defined by aerobic and anaerobic microbial processes. An understudied part of the CH4 cycle in northern peatlands are anaerobic CH4-oxidizing processes (AOM) to mitigate CH4 emissions. Particularly, AOM processes of recent discovery, such as those dependent on the reduction of organic electron acceptors such as natural organic matter (NOM), namely NOM-dependent AOM (NOM-AOM), have never been studied in these sites despite the evidence showing significant amounts of NOM and CH4 emissions coexisting in peatland areas. Here we therefore developed a strategy to discern the role of NOM in determining the emission of CH4 towards the atmosphere by means of several mechanisms of CH4 production and consumption prompted by fractions of in-situ NOM found in the Stordalen mire (Abisko, Sweden), a model field site for permafrost-thaw affected northern peatlands. The overall goal of this proposal is to dissect the role of dissolved and particulate fractions of NOM (DOM and POM) in fueling or suppressing the production and consumption of CH4 in bog and collapsing palsa areas. Such sites have previously been detected as spots possessing significant amounts of organic matter coexisting with substantial CH4 emissions. In work package 1 (WP1), bulk peat will be collected together with in-situ geochemical data. The sampled peat will be used to isolate DOM and POM fractions, with the purpose of performing an in-depth physicochemical characterization employing state-of-the-art analytical techniques, including DOC and TOC determination, FTIR characterization, and electron exchange capacity measurements. In WP2, isotopic tracing experiments will be performed in microcosms inoculated with peat and enriched with isolated DOM or POM to discern their role in prompting or suppressing acetoclastic and hydrogenotrophic methanogenesis, as well as fueling the consumption of CH4 in NOM-AOM. In WP3, the identity and relative abundance of the microorganisms involved in the studied CH4-cycling processes, as well as the functional genes involved, will be analyzed by means of DNA- and RNA-based molecular techniques, such as 16S high-throughput sequencing and quantification of transcripts related to methanogenesis and methanotrophy. We foresee that depending on its physicochemical properties, NOM may both contribute but also mitigate the emission of CH4 in permafrost thaw affected peatlands.

• DFG Programme: Research Grants