Microbial iron cycling in permafrost peatlands affected by global warming - Impact on carbon mobilization and greenhouse gas emissions

• Main Author: Patzner, Monique Sézanne
• Other Authors: Kappler, Andreas (Prof. Dr.)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Tübingen 2023
• Subjects: 500; 550; 570; Auftauender Permafrost; Moore; Eisen; organischer Kohlenstoff; Abisko; Arktik; peatlands; iron; soil organic carbon; Arctic; Thawing permafrost; Stordalen; Global warming; Ice; Northern Sweden; palsa; permafrost; Subarctic
• Online Access: http://hdl.handle.net/10900/121085; https://doi.org/10.15496/publikation-62452; http://nbn-resolving.de/urn:nbn:de:bsz:21-dspace-1210854

Northern Hemisphere peatlands store vast amounts of carbon, particularly in permafrost regions where low temperatures inhibited organic matter decomposition since the last glacial ice age. With high latitudes warming faster than anywhere else on the planet, there is urgent concern about the impact of permafrost thaw on the stability of this carbon sink. It has been shown that iron(III) (oxyhydr)oxides can trap organic carbon in soils, underlain by intact permafrost, which may limit carbon mobilization and thus its degradation. Therefore, it is considered as a so-called rusty carbon sink. However, controls on the stability of iron-carbon associations in permafrost peatlands and their response to warming temperatures are poorly understood. Only little is known about the microbial iron cycle in permafrost peatlands and how it is impacted by global warming. Its consequences for carbon mobilization and ultimately greenhouse gas emissions such as carbon dioxide and methane prevail unexplored. Aiming to fill these knowledge gaps, we characterized the dynamic interactions between iron and carbon in a subarctic thawing permafrost peatland (Stordalen mire) in Abisko, Northern Sweden. Here, in the discontinuous permafrost zone, oxic palsa mounds with ice-rich cores are rapidly collapsing into acidic bogs before they ultimately transform into ice-free fen-type wetlands. We show that reactive Fe minerals such as iron(III) (oxyhydr)oxides bind significant quantities of organic carbon (up to 20% of total organic carbon) in areas of intact permafrost. However, these iron-carbon associations are not stable during permafrost thaw. Iron(III)-reducing bacteria, such as e.g. Geobacter spp., reductively dissolve iron(III) (oxyhydr)oxides coupled to carbon oxidation, and release aqueous iron (iron(II)) and the previously iron-bound, aliphatic-like organic carbon that becomes mobilized. The microbially driven iron(III) reduction thus directly contributes to greenhouse gas emissions such as carbon dioxide by iron(III) reduction coupled ...