Soil bacterial and fungal communities along a soil chronosequence assessed by fatty acid profiling

Microbial communities are important components of terrestrial ecosystems. The importance of their diversity and functions for natural systems is well recognized. However, a better understanding of successional changes of microbial communities over long time scales is still required. In this work, the size and composition of microbial communities in soils of a deglaciation chronosequence at the Damma glacier forefield were studied by fatty acid profiling. Soil fatty acid concentrations clearly increased with soil age. The abundances of arbuscular mycorrhizal fungi (AMF), bacteria and other soil fungi, however, were more affected by abiotic soil parameters like carbon content and pH than by soil age. Analysis of ratios of the different microbial groups (AMF, fungi, bacteria) along the soil chronosequence indicated that: i) the ratios of AMF to bacteria and AMF to fungi decreased with soil age; and ii) the ratio of fungi to bacteria remained unchanged along the soil chronosequence. These two pieces of evidence suggest that the evolution of this ecosystem proceeds at an uneven pace over time and that the role of AMF is less important in older, more organic and acidified soils than in mineral soils. In contrast to other studies, no successional replacement of bacteria with fungi in more acidified and organic soil was observed.