Influence of sand burial on cultivable micro-fungi inhabiting biological soil crusts

We examined the influence of sand burial of 0.5-mm and 10-mm depths on micro-fungal communities inhabiting moss-dominated and mixed biocrusts in the vicinity of the Shapotou Research Station in the Tengger Desert, China. The buried communities were compared with those in unburied crusts, as well as with the sandy below-crust and topsoil communities. We isolated 65 fungal species belonging to 43 genera using the soil dilution plate method. Compared to the unburied communities, the buried crust communities were characterized by lower abundance of melanin containing species, especially those with large many-celled conidia, but higher abundance of species producing small light-colored and one-celled conidia, mainly mesophilic Penicillium spp. Sand deposition also caused reduction of isolate density that was more pronounced in the mixed crusts. Diversity characteristics of micro-fungal communities and isolate densities varied in the two crust types in response to the same level of sand burial. This difference between the mixed and moss-dominated crusts was less expressed when the communities had been subjected to the deep sand burial. Below-crust sandy communities showed a more significant decrease both in isolate density and species richness compared to buried crust communities, which was accompanied by the substitution of dominant species - the thermotolerant Aspergillus fumigatus in the subcrust sandy layers instead of melanized species with large multicellular conidia in the crusts. On the whole, the influence of sand burial on crust micro-fungal communities was likely associated with the shielding effect of sand layer which might protect the crust layer from evaporation and UV-radiation. Whereas sand deposition in the crusts partly changed the substrate quality and microclimatic conditions for soil micro-fungi, transition from the crust to the below-crust sandy layer much more substantially altered the environmental situation (mainly in nutrient status, from the comparatively rich organic crust layer to the poor mineral sandy layer) thus leading to the more significant changes in the micro-fungal communities.