Soil fungi exhibit taxon-specific preferences for distinct particle size fractions

Soil particle size fractions (PSFs), i.e. clay, fine silt, coarse silt, and sand together with particulate organic matter (POM), differ in their mineralogical and organic composition and thereby in their sorption and desorption of biotic and abiotic compounds. Utilizing a soil fractionation protocol based on gentle ultra-sonication, wet-sieving and centrifugation, previous studies on soil variants from a long-term fertilization field study demonstrated the preference of most dominant soil bacteria to be associated with a specific soil PSF, which was not altered by soil modifications induced by long-term fertilization. In this study the same experimental set-up was used to analyse the fungal preference for PSFs. Fungal diversity was analysed by qPCR and high-throughput sequencing of the internal transcribed spacers from soil DNA. Fungal community composition retrieved from the non-fractionated soil and the pooled data of the different PSFs only differed by a maximum of 6.4 %, indicating that the fractionation protocol was sufficiently accurate to recover most fungi. The diversity of fungal taxa differed significantly between the PSF. The sand/POM fraction enriched for several species of Dethideomycetes and Cadophora. Several members of Sordariomycetes had their highest abundance in fine silt and Penicillium and Mucoraceae were most abundant in the clay fraction. In contrast clay was depleted in sequences of Sordariales, and Mortierella was less abundant in the sand/POM fraction. Despite uncertainties related to cross-contamination of PSF and anticipated simultaneous interactions of fungal hyphae with different PSF, our data suggest that a majority of dominant soil fungal taxa show clearly pronounced, environmentally stable preferences for specific PSF.