Bacterial and fungal communities in depths of the Damma soil chronosequence

Spatial patterns of microbial communities have been extensively surveyed in well-developed soils, but few studies investigated the vertical distribution of microorganisms in newly developed soils after a glacier retreat. We used 454-pyrosequencing to assess whether bacterial and fungal community structures differed between stages of soil development characterized by an increasing vegetation cover from 0 (barren), 13 (sparsely-vegetated), 60 (transient) to 95% (vegetated) (10, 60, 80 and 110 years) and depths (surface, 5 and 20 cm) along the Damma glacier forefield (Switzerland). Soil age significantly influenced the bacterial and fungal community structures. Barren soils were characterized by metabolically versatile bacteria (e.g. Geobacter) and psychrophilic yeasts (e.g. Mrakia). Vegetated soils were characterized by higher root biomass and bacteria able to degrade complex organic compounds (e.g. Candidatus Solibacter), ligno-cellulolytic Ascomycota (e.g. Geoglossum) and ectomycorrhizal Basidiomycota (e.g. Laccaria). Soil depth influenced the bacterial and fungal communities in the barren and sparsely-vegetated soils, partly due to more silt and higher soil moisture in the surface. In both soil ages, the surface was characterized by OTUs affiliated to Phormidium and Sphingobacteriales. In lower depths, however, bacterial and fungal community compositions differed between both soil ages. Lower depths of sparsely-vegetated soils consisted of OTUs affiliated to Acidobacteria and Geoglossum whereas depths of barren soils were characterized by OTUs related to Gemmatimonadetes. Overall, our study shows that microbial communities vary with soil depth in barren soils while they do not differ between depths in vegetated soils indicating that plant establishment might also drive the vertical distribution of microbial community structures in recently deglaciated soils.