Biodiversity and ecology of microbial communities in Patterned Grounds

Patterned Grounds (PGs) are formed on permafrost soils as a result of cryoturbation. The mixing, heaving, and churning of soil that occurs during freeze-thaw cycles forms stripes, circles, polygons and nets with and without visible surface textural sorting. Although several studies described PG features and their formative processes, microbiological aspects are yet greatly unexplored. Microbial communities that develop in these ecosystems may play important roles in nutrient availability, dynamics and stabilization and therefore in plant colonization and ecosystem evolution. In this study, microbial community structure in circular PGs was assessed in terms of biodiversity and ecology from four areas, characterized by different lithotypes, in the Graian Alps (North-western Piedmont and Valle d’Aosta regions). Samples were subjected to phylogenetic fingerprint by Denaturing Gradient Gel Electrophoresis (DGGE). Moreover, abundance of bacterial, archaeal and fungal genetic markers and functional genes was measured by quantitative real-time PCR (qPCR) and correlated to chemical parameters. Results indicate that PGs are habitats composed by different ecological niches that allow the growth of phylogenetically and metabolically diverse microbial groups. Microbial populations show a clear concentric distribution, correlated to C:N ratio, influenced by lithology of parent material and coherent with trends of physicochemical parameters within PG circles. Several phylotypes, common to other PGs or cold edaphic environments were found. These first results, underlying the importance of cryoturbation phenomenon in shaping microbial community structure in seasonally frozen soils, seems to confirm the pertinence of PGs as small-scale models for studies on microbiological processes affecting the evolution of periglacial alpine ecosystems.