Soil formation and initial microbiological activity on a foreland of an Arctic glacier (SW Svalbard)

- Bacterial community richness increased along the chronosequence while the total cell count decreased.
- The biovolume and number of viable cells decreases across the chronosequence.
- Glacier supply increases the cultivable bacteria number and their species richness.
- Soil development is related to bacterial community composition, soil structure and available water.

The initial microbiological activity on the forefield of the continuously retreating Werenskiold glacier (West Spitsbergen) along the chronosequence was investigated using both culture-dependent and culture-independent approaches. The prokaryotic cell parameters: total cell number (TCN g−1 d.w.), biomass (μg C g−1 d.w.), average cell volume (ACV, μm3), morphological structure (% cocci, rods, curved cells in TCN) and the contribution of viable cells with intact membrane (% in TCN) were established. The number of opportunistic bacteria (CFU g−1 d.w.) was counted using plate culture methodology. The PCR-DGGE of amplified 16S rRNA gene fragments and sequencing were also used to analyse the total (native soil samples) and culturable (plate wash samples) bacterial community structure. A total of 33 partial 16S rRNA gene sequences were obtained from the excised DGGE bands, with the majority of the sequences closely related to Actinobacteria, Bacteroidetes, and Proteobacteria (β and γ) groups. A high proportion of cultured and uncultured Arthrobacter in the studied glacier foreland soil confirms their role in the initiation of soil formation processes. Changes in the structure of both the native soil samples and wash plate samples communities along the chronosequence indicated their participation in young soil formation. Although initial microbial activity is closely associated with a higher proportion of non-cultivated bacteria, less numerous cultivated bacterial strains also feature significantly in the biodiversity. The main factors positively affecting TCN, BB, CFU, and the contribution of viable cells were water, nitrogen, carbon and organic matter content in the soil. In our study we have shown that a large share of the finest-particle-size fractions in the soil (dust, clay) negatively affects the BB and CFU. The native soil samples number of operational taxonomic units (OTUs) was mostly dependent on the pore water composition, and the C:N ratio in the soil, the wash plate samples number of OTUs was mostly connected with organic matter and soil water content.