Can iron-metabolizing bacteria control the fate of carbon during permafrost thaw?

• Applicant: Professor Dr. Andreas Kappler
• Subject Area: Soil Sciences
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448755787

High latitude permafrost peatlands store around 14% of Earth’s soil carbon stocks despite covering only around 3% of the land surface. These large organic carbon stores make high latitude peatlands disproportionately important for climate feedback mechanisms, especially considering that the northern hemisphere is experiencing above average rates of warming. There is much concern that permafrost thaw may release stored organic carbon and allow it to be emitted as CO2 and CH4, potentially further exacerbating climate warming. Additionally, hydrological changes associated with permafrost thaw eventually lead to waterlogged soils under which high methane emissions are observed. It has been observed by us and others, that reactive soil minerals may play a key role in carbon stabilization in intact permafrost as is observed across many different soil and sediment environments. Indeed, in our previous work we have shown that up to 20% of carbon in certain soil horizons in our model field site, a Swedish permafrost peatland, could be bound to reactive, poorly crystalline Fe(III) (oxyhydr)oxides. However, this “rusty carbon sink” is rapidly de-stabilized during permafrost thaw due to microbial mineral reduction. This raises many unanswered questions regarding how the dynamics of Fe and C cycling change during permafrost thaw, and the effect of iron mineral formation and dissolution on carbon sequestration and greenhouse gas emissions which we will address in this proposal. Specifically, in a first step we will determine the amount, identity, quality and bioavailability of carbon (organic compounds) associated with iron minerals at different thaw stages and we will identify, quantify and isolate the iron(II)-oxidizing and Fe(III)-reducing microorganisms involved in formation and destruction of carbon-binding iron minerals. In a second step we will then quantify the extent to which formation and destruction of iron minerals, and thus carbon release and increased bioavailability, influences greenhouse gas emissions (CO2 and CH4).

• DFG Programme: Research Grants