How is carbon stored in boreal forest soils? - A method development which investigates at what protein concentration ferrihydrite and goethite are saturated.

Abstract: Boreal forests store the majority of their carbon in the soil and play an important role in the global carbon cycle. However, the mechanisms that control carbon storage in boreal soils are not well understood. In recent studies, there has been a specific focus on how ectomycorrhizal (ECM) fungi influence carbon dynamics in boreal forests, particularly through their nitrogen acquisition. A major part of the nitrogen in boreal forests is present in organic form, as proteins, and adsorbed on soil minerals. However, it is generally unknown whether the ECM fungi can access this nitrogen. In this study, a laboratory method development was carried out. This provided useful information for future studies which can investigate if ECM fungi can acquire nitrogen from proteins adsorbed on two common iron oxide minerals in boreal forests. Concretely, the maximum adsorption of the protein Bovine serum albumin (BSA) on ferrihydrite and goethite was investigated. The result of this study showed that goethite is saturated at 0,58 mg BSA/ml goethite and ferrihydrite at approximately 1,25-1,3 mg BSA/ml ferrihydrite. This result was consistent with the hypothesis which stated that ferrihydrite, with its larger surface area compared to goethite, would have a greater capacity to adsorb proteins. These results can subsequently be used to create films with different protein loadings on minerals which then can be used to study if ECM fungi can acquire nitrogen from protein-mineral complexes. By studying this, we can increase our understanding of soil carbon storage and tree growth in boreal forests, as nitrogen is a limiting nutrient for tree growth.