Soils of seasonally snow-covered ecosystems sequester an important pool of organic carbon, which is particularly sensitive to global changes. One concern is the biomineralisation of this carbon pool by micro-organisms, especially in relation with the dynamics of snow cover. Our aim was to study the influence of snow-induced soil temperature regime and litter quality on soil microbial communities in temperate alpine ecosystems. We compared two alpine meadows which strongly differ for their snow cover duration: an early snowmelt alpine meadow dominated by Kobresia myosuroides and a late snowmelt site dominated by Carex foetida. Soils of early snowmelt sites are frozen most of the winter, while the snowpack maintains the winter temperature of the late snowmelt soils around 0°C. We sampled soil cores seasonally and total DNA was extracted. Firstly, we analyzed both the prokaryotic (bacterial and chrenoarcheotal) and fungal communities using CE-SSCP molecular markers. The Edward’s distance of normalized SSCP profiles was calculated and distance trees were constructed by Neighbour Joining method. Microbial communities from early snowmelt sites strongly differed from those of late snowmelt sites. Marked seasonal variations were also detected within each site. However, similarities between both sites were noticeable for soils sampled under snowpack. Secondly, we constructed marker libraries for bacterial (16S ARN gene) and fungal (ITS1 and 28S) communities. At least 300 clones were sequenced for each sampling. Sequence analyses confirmed strong spatial and seasonal variations. Early snowmelt sites are particularly rich in Actinobacteria which is consistent with the presence of recalcitrant carbon sources. Late snowmelt sites are dominated by Acidobacteria and this is particularly striking for soils sampled under snowpack at the end of winter. To conclude, we discussed the relationships between diversity patterns and functioning of alpine soils. In particular, we attempted to articulate these diversity patterns with the results from a three-year litter bag experiment examining litter decomposition in the same early and late snowmelt sites.

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