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%) deglaciated after 1979 in the foreland of the Ecology Glacier and a Cambic Cryosol (vegetation cover of 100%) distal to the lateral moraine deglaciated before 1956 were investigated by combining soil chemical and microbiological methods. 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, such as initial silicate weathering indicated by a decreasing Chemical Index of Alteration with depth. Differences in the development of these initial soils could be related to different microbial community compositions and vegetation coverage, despite the short distance among them. We observed—decreasing with depth—the highest bacterial abundances and microbial diversity at vegetated sites. Multiple clusters of abundant amplicon sequence variants 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.
Highlights
Retreating glaciers in polar and mountainous regions reveal proglacial terrain that is exposed to soil formation and subsequently colonized by microorganisms and p lants[1,2,3,4]
A recent study in the foreland of the Ecology Glacier on King George Island demonstrated that the diversity and properties of microorganisms in recently deglaciated areas are related to age and to differences in soil stability within the upper centimeters due to the influence of cryoturbation[39]
The complete surface of KGI D was covered with Deschampsia antarctica, Polytrichum spec., Colobanthus quitensis, and Usnea antarctica. 14C dating showed that the humin fraction of soil organic matter in profile KGI C was formed after the melting of the glacier in 1979 (92.2% 1992–1995 cal AD (− 43 to − 46 cal BP); 3.2% 1957 cal AD (− 8 cal BP)), whereas the humin fraction of the upper 3 cm in profile KGI D is much older (95.4% 1954–1956 cal AD (− 5 to − 7 cal BP)) (Supplementary Table S3)
Summary
Retreating glaciers in polar and mountainous regions reveal proglacial terrain that is exposed to soil formation and subsequently colonized by microorganisms and p lants[1,2,3,4]. By substituting space with time, chronosequences of proglacial environments are an important tool to understand primary succession and soil forming processes[5], and were used to study the succession of soil microbial communities and their influence on initial soil formation in the past[6,7,8]. Such microbial populations with different abundances, community structures and diversities are among the first organisms to colonize recently deglaciated areas[9,10,11]. We combined grain size and pedochemical analyses with DNA-based molecular biological analyses, including high-throughput sequencing and quantitative PCR, to determine the diversity, distribution, and abundance of microbial communities
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