Artificial soil studies reveal domain-specific preferences of microorganisms for the colonisation of different soil minerals and particle size fractions.

Artificial soils were used in this study to analyse the importance of different mineral compositions for the diversity of soil microorganisms. Variants containing montmorillonite (MT), illite (IL) and illite + ferrihydrite (IL+FH) were compared to each other. Bulk material and their particle size fractions, as obtained by ultracentrifugation and wet-sieving, were characterised for abundance and diversity of Bacteria, Archaea and Fungi. Samples were analysed 6 and 18 months after inoculation with sterilised manure and a soil-extracted microbial community. Generally, IL, and even more pronouncedly IL+FH, supported the growth of more Bacteria, Archaea and Fungi, than MT. This trend was most pronounced in the finest fraction (< 20 μm). The structural diversity of Fungi responded more strongly to the different mineral compositions than the Bacteria, for which particle size fractions were more important. Archaea established a specific community in the finest fraction and showed no response to the different mineral compositions. Overall, this study demonstrates that the mineral composition and the particle size fractions have specific and different selective effects on the three domains and, thus, suggests that these factors strongly contribute to niche separation and the high diversity of microbial communities in natural soils with complex mineral compositions.