Organic matter composition and dynamic in polygonal tundra soils

• Main Author: Höfle, Silke Tamara
• Format: Doctoral or Postdoctoral Thesis
• Language: German; English
• Published: 2015
• Subjects: ddc:550; Arctic; Global warming; lena delta; permafrost; Tundra
• Online Access: https://kups.ub.uni-koeln.de/6184/; https://kups.ub.uni-koeln.de/6184/4/Promotion_Hoefle_2015-07-14.pdf

Arctic permafrost regions are postulated to be most strongly affected by the on-going global warming resulting in longer summer seasons and higher temperatures. This may cause the degradation of permafrost and increase the thickness of the annual superficial thawing layer (active layer) of permafrost soils. Thereby permafrost soils may turn from carbon sinks into carbon sources for the atmosphere as large, previously frozen carbon pools become available for microbial degradation, a key factor in the soil organic matter (OM) degradation. The aim of this thesis was to investigate soil organic matter of permafrost soil to identify stabilization mechanisms, soil bacterial communities and carbon pools preferably metabolised by soil bacteria using bulk, molecular lipid-biomarker, physical fractionation and radiocarbon analysis. In temperate soils stabilization mechanism of OM, mainly organo-mineral associations and soil aggregations, are well studied by separating the OM into functional pools with different turnover rates, which are determined by their chemical properties and bioavailability. However, little is known about the quality of the soil OM, its stability and its accessibility for the microbial community in permafrost soils. The most important location for microbial metabolic activity in permafrost soils is the active layer. Therefore, this thesis concentrated on investigating different soil horizons of the active layer and the still frozen permafrost top layer of the polygonal tundra in the Siberian Lena Delta, Russia. Soil samples were predominantly taken from Samoylov Island and for the characterisation of soil bacterial communities additional samples from Kurungnakh Island were also analysed. The results show that the OM of both different cryogenic structures (polygon rim and centre) on Samoylov Island is dominated by little-decomposed, higher plant-derived material as indicated by the dominance of long-chain lipid biomarkers (n-alkanes and n-fatty acids) and high C/N ratios (16-51). The bulk soil OM of ...