Decomposition and Sequestration of Organic Matter in Fine-Sized Fractions Modified By Clay Mineral Composition.

The study of interactions between minerals, organic matter (OM) and microorganisms is essential for the understanding of soil functions such as OM turnover. Here, we present an interdisciplinary approach using artificial soils to study the establishment of the microbial community and the formation of macroaggregates as a function of the mineral composition by using artificial soils. The defined composition of a model system enables to directly relate the development of microbial communities and soil structure to the presence of specific constituents. Five different artificial soil compositions were produced with two types of clay minerals (illite, montmorillonite), metal oxides (ferrihydrite, boehmite) and charcoal incubated with sterile manure and a microbial inoculum derived from a natural soil. The so produced soil-like systems have OM dynamics comparable to the natural soil incubated in a laboratory experiment. After additional OM and longer incubation time we found a re-formation of macro-aggregates which was significantly higher when montmorillonite was present. Even though different bacterial communities were established depending on the artificial soil composition, the amount and quality of the OM did not show significant differences supporting the concept of functional redundancy. The decomposition of newly added plant litter was affected by the type of clay mineral that formed the artificial soils, as the montmorillonite-derived soil exhibited a slower mineralization and lower microbial biomass compared to the illite-soil. Although a high specific surface area (SSA) provides a high sequestration capacity for C and N, smaller amounts were sequestered in the montmorillonite soil with a higher SSA compared to the illte soil. We thus conlcude that a more intensive decomposition is associated with a higher microbial biomass leading to higher amounts of microbial products sequestered in the clay‐sized fraction. The effect of the clay minerals seemed to become evident only in developed artificial soil systems after several OM additions.