From death of a glacier to the beginning of life in soil: a case study in the Swiss Alps.

Pedogenesis starts just after deglaciation, with microbial primary succession playing a key role in soil ecosystem development. The progressively exposed moraines of the Morteratsch Glacier (Upper Engadine, Switzerland) offer a full time sequence, from 0 to 150 yrs [1]. We assessed geological, physico-chemical and microbiological parameters (microbial biomass, microbial community structure and selected soil enzyme activities) along the age gradient of the proglacial area. We set up a double-nested-PCR-DGGE approach on intracellular DNA extracted from the topsoil (0- 10 cm) to monitor bacterial and fungal succession along the chronosequence, capable to detect also low numbers of target sequences occurring in early stage soils. Increasing soil age was characterized by microbial biomass increase and, as expected, by a dynamic community succession. Both parameters displayed in turn a high positive correlation with SOM content (Ntot and Ctot) and pH decrease (0 yrs: pH 8.11 – 150 yrs: pH 5.64). High correlations with enzymes, biochemical markers reflecting soil activity, were also detected. Numbers of microbial phylotypes were lowest in the youngest soils (0-4 yrs), increased in the intermediate aged soils (4-110 yrs), and decreased again and plateaued in the oldest soils (110-150 yrs). Our findings confirm that soil microbiota undergo drastic variations both in terms of biomass and community composition according to substrate availability, with interactive adaptation to the differing stages of soil development.