Characterization of Buried Soil Organic Matter

Burial of topsoil soil organic matter (SOM) constrains its decomposition due to a combination of environmental conditions and physical and chemical processes, such as increased soil wetness, decreased aeration, as well as increased compaction and physical protection of the deposited organic matter within newly formed aggregates. The research proposed for this fellowship focuses on buried SOM in different ecosystems: agricultural systems in which SOM is buried by tillage or erosion, and Arctic systems in which SOM is buried by freezing (cryoturbation). Because different processes are involved in the burial of SOM, differences in the formed pools of buried SOM are expected. Four hypotheses will be tested during the proposed project concerning differences between physical and biochemical properties and labile proportions of buried SOM (hypotheses #1 and #2), and factors limiting decomposition of the labile proportions of buried SOM (hypotheses #3 and #4). Density fractionation in combination with particle-size and aggregate separation will be used to isolate labile and stable fractions of SOM which will be biochemically characterized; as well incubation experiments on whole soil and SOM fractions and water extracts will be used to characterize buried organic carbon and its stability. Some work will be directed towards characterizing soil light fractions because they are suggested to represent the labile carbon pools; hence they provide crucial information about a specific pool of SOM which may be quite vulnerable to alteration and/or mineralization. Incubation experiments will provide information about the biologically available carbon in the various fractions. Rock-Eval pyrolysis will provide information about thermal stability of SOM and about its fragments released during pyrolysis and amino sugar analyses will deliver information about accumulation of microbial residues. Furthermore, alkaline extracts of selected samples will be examined and determinations with KMnO4 will be applied to evaluate the labile SOM from a chemical perspective and to evaluate whether the information obtained is complementary to that provided by the biological assessments. Spectroscopic measurements with 13C-NMR, X-ray Absorption Near Edge Structures (XANES) and mid-infrared spectroscopy will provide molecular information on selected soil samples and fractions. The data obtained in this study together with some simple model calculations will help improve our understanding of the vulnerability of buried SOM to potential loss by management practices, land use change and a warming climate. Together with the completion of characterization of SOM (continuation of modelling, mid-infrared spectroscopy, alkaline extracts, determinations of labile proportions of SOM with KMnO4) the remaining time during the return phase will be used for the elaboration of a further proposal to apply the gained knowledge on a question located in Austria, for the report of the finished project and publishment of the obtained results in peer-reviewed scientific journals.