Influence of microorganisms on initial soil formation along a glacier forefield on King George Island, maritime Antarctica

Abstract. Compared to the 1970s, the edge of the Ecology Glacier on King George Island, maritime Antarctica, is positioned more than 500 m inwards, exposing a large area of new terrain to soil-forming processes and periglacial climate for more than 40 years. To gain information on the state of soil formation and its interplay with microbial activity, three hyperskeletic Cryosols (vegetation cover of 0–80 %) in the recently (< 50 years) deglaciated foreland of the Ecology Glacier and a Cambic Cryosol (vegetation cover of 100 %) behind a lateral moraine deglaciated more than 100 years ago were investigated by combining soil chemical and microbiological methods. All soils are formed in the same substrate and have a similar topographic position. In the upper part of all soils, a decrease in soil pH was observed, but only the Cambic Cryosol showed a clear direction of pedogenic and weathering processes. Differences in the development of these initial soils could be related to different microbial community composition and vegetation coverage, despite the short distance among them. We observed – decreasing with depth – the highest bacterial abundances and microbial diversity at vegetated sites. All soils were dominated by bacterial phyla such as Proteobacteria, Actinobacteria, Bacteroidetes, Acidobacteria, Verrucomicrobia, and Chloroflexi. Multiple clusters of abundant OTUs were found depending on the site-specific characteristics as well as a distinct shift in the microbial community structure towards more similar communities at soil depths > 10 cm. In the foreland of the Ecology Glacier, the main soil-forming processes on a decadal timescale are acidification and accumulation of soil organic carbon and nitrogen, accompanied by changes in microbial abundances, microbial community compositions, and plant coverage, whereas quantifiable silicate weathering and the formation of pedogenic oxides occur on a centennial to a millennial timescale after deglaciation.