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Active layer characteristics and bacterial occurence across a latitudinal gradient in Victoria Land (continental Antarctica) as indicator of functional processes in permafrost environments and ecosystems

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Citation:
Cannone, N. , Guglielmin, M. , Wagner, D. and Hubberten, H. W. (2005): Active layer characteristics and bacterial occurence across a latitudinal gradient in Victoria Land (continental Antarctica) as indicator of functional processes in permafrost environments and ecosystems , Second European Conference on Permafrost, EUCOP 2005, PotsdamJune 2005. .
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Abstract:

Soil analyses have been carried out in permafrost environment in Victoria Land, Continental Antarctica, in 9 sites within the network of the sensitive system permafrost-vegetation for the assessment of climate change effects along a latitudinal and geographical transect (77° - 72°S). Within each site the samples have been collected in different ecological and environmental conditions concerning active layer thickness, vegetation type and coverage, substrata, occurrence of glacial and periglacial features. In each site the vertical profile of the ground have been described and the samples collected within the active layer representing all the layers with visible differences regarding texture, structure and color. Organic C and N show specific patterns allowing to discriminate: a) vegetated vs unvegetated sites; b) among the unvegetated sites, ground with and without disturbance processes, mainly represented by frost heave and salt concrections. The barren grounds with frost heave and/or salt efflorescences show highest values of organic C and N. In the vegetated sites, organic C and N show different patterns related to the vegetation type and to their ecological requirements in terms of nutrient regime. The higher values are associated in particular with moss communities and with ground colonized by nitrophytic epilithic lichens. On inundated grounds the content of both organic C and N increases respect to close sites with similar vegetation. On the contrary, bacteria have a wide range of variability (between complete sterile soils to a more than 100K of cells/g soil) with less clear patterns of spatial distribution. In the surficial layers (< 5cm) in the unvegetated sites the higher bacteria values couple with the higher values of Al and Fe, but not with the organic C and N. In these sites the higher bacteria values are always associated to the more xeric conditions while the only really sterile site is the true inland one (Cape Sastrugi). Although the vegetated sites show more abundant bacteria, the highest values have been found within unvegetated gelifluction terracettes soils. The vertical distribution of the measured parameters show regular patterns, with lower values at the surface, maximum at intermediate depth, and a decrease in the deeper parts of the profile, except for C and N in some sites with a progressive decrease with depth. These depths are consistent with the values of active layer thickness characterizing the different sites. The vertical profile of the bacteria are differentiated between vegetated soils and barren grounds, the former with the higher values in the upper layers, the latter with an opposite pattern. The relatively high values of bacteria in barren grounds and in strongly disturbed soils (as gelifluction terracettes) need further research especially because in literature these Antarctic environments have been considered sterile and therefore not particularly sensitive to the climate change.

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