Minerals provide reactive surfaces in soils to which organic matter and nutrients can bind and are thereby protected from decomposition, mineralisation, and leaching. Many soil microorganisms are living attached to mineral surfaces, where they form a unique habitat, the so-called mineralosphere. The interplay of microbial colonization, and sorption and release of organic matter and nutrients cause continuous changes and transformations within the mineralosphere, with immediate consequences for carbon and nutrient storage and availability in soil. How land use and associated changes in biodiversity affect these interactions and resulting differences in soil carbon and nutrient stocks are hardly understood.
Therefore we installed mineral bags filled with pure, carbon-free mixtures of sand and illite (clay mineral) or goethite (iron oxide) at 5 cm depth at all experimental sites (EPs) of the Biodiversity Exploratories in 2015. At all very intensive sites, additional bags were installed at 25 cm depth and for forests also directly below the litter layer to determine the role of soil depth.
After five years of field incubation, the bags are now being retrieved as well as surrounding soil. We aim at exploring the co-occurrence of mineral-associated microbial communities, organic matter, and nutrients in a coordinated, interdisciplinary approach. We hypothesize that type and intensity of land use and biodiversity affect: (1) the accumulation and quality of mineral-associated organic matter, (2) the contribution of plant and microbial sources to mineral-associated organic matter, (3) the patterns of microbial communities emerging in the mineralosphere, (4) the preservation mechanisms of mineral-associated organic matter, (5) the nutrient accumulation in the mineralosphere, and (6) the soil depth-related differences in mineralosphere.
The mineral and soil samples will be analyzed complementary with a suite of state-of-the-art surface-sensitive, biogeochemical, isotopic, mineralogical, and microbiological methods. This collaborative approach will allow for the first time in-depth insight into developing mineralospheres under natural environmental conditions and real land use intensities.