Soil fungal community assembly in a primary successional glacier forefront ecosystem as inferred from rDNA sequence analyses

Soil fungal community assembly in nonvegetated areas on the forefront of a receding glacier was analyzed by cloning of the PCR-amplified partial small subunit (18S) of the ribosomal RNA genes (rDNA) from soil DNA samples. Fungal sequences obtained from areas adjacent to the present glacier terminus (young substrate) represented three fungal phyla, whereas those obtained adjacent to the terminal moraine (old substrate) were distributed among Ascomycetes and Hymenomycetes. The cloned sequences from both substrates represented mainly filamentous ascomycetes or basidiomycetes with a likely affinity to Agaricales. Unexpected biotrophic fungi with affinities to Taphrinomycetes, Urediniomycetes (the rust fungi) and Ustilaginomycetes (the smut fungi) plus an unknown, likely chytridiomycetous group were detected exclusively in the young substrates. These observations of biotrophic fungi are attributed to an aerially deposited, dormant spore bank, which may also be present in the older substrate but is masked by larger active mycelial biomass. This study underlines the importance of stochastic events and airborne spore deposition in the assembly of early fungal communities.