Bacterial and fungal community responses to reciprocal soil transfer along a temperature and soil moisture gradient in a glacier forefield

The influence of soil physicochemical properties on microbial communities can be large, especially in developing soils of glacier forefield chronosequences. However, small-scale expositional differences in bare soils and their impacts on soil microbial communities have so far been largely neglected. Here we studied the changes of microbial communities in three deglaciated unvegetated sites along a soil moisture and temperature gradient near a glacier terminus. In order to elucidate the driving forces for these changes, fine granite sediment was reciprocally transferred and regularly sampled during 16 months to determine microbial activities and the bacterial and fungal community structures and compositions using T-RFLP profiling and sequence analysis. Microbial activities only responded to soil transfer from the warmer and drier site to the colder and moister site, whereas the bacterial and fungal community structures responded to transfer in both directions. Bacterial phylotypes found to react to soil transfer were mainly the Acidobacteria, Actinobacteria, alpha- and beta-Proteobacteria. The common fungal phylogenetic groups Pezizomycetes and mitosporic Ascomycetes also reacted to soil transfer. It seemed that the soil moisture was the limiting factor for the microbial activities. We concluded that for the microbial community structures transferring soil from a colder to a warmer site induced a higher rate of change due to a higher microbial activity and faster species turnover than the reverse transfer.

► Different microbial community structures with changing soil moisture and temperature.
► Different microbial activities with changing soil moisture and temperature.
► In a glacier forefield the exposition to the sun determines the microbial activity and structure.
► Microbial activities react less to environmental changes than community composition.
► Soil moisture determines microbial activities and composition in bare soil.