Morten Dencker Schostag:
Permafrost affected soil systems represent 17% of the global land area. It has been shown that these soil systems contain a large amount of organic carbon that have the risk to be released as greenhouse gasses to the atmosphere by microbial processes. The active layer of soil overlaying permafrost in the Arctic is subjected to dramatic annual changes in temperature and soil chemistry, which may affect microbial community both in structure and activity. However there is only sparse knowledge on the responses of the microbial community where the soil is being thawed and frozen during seasonal change in the active layer permafrost.
The main focus of this thesis was therefore to investigate the microbial community composition in the active layer permafrost and the expressed functions during temperature changes, i.e. seasonal changes and a more refined analysis during thawing and freezing. The objective was further to investigate the turnover time for taxonomic marker 16S rRNA transcripts in soil at different temperature.
The findings of the thesis resulted in five manuscripts. Manuscript I investigated the microbial community and showed a distinct community for both winter and summer. The microbial community composition was more homogenous in the winter samples compared to summer samples. Manuscript II showed that contamination from top soil layer was detected in permafrost core samples. Therefore we developed a protocol for determining and avoiding contamination during post-drilling procedure to prevent contamination in future permafrost sampling. Findings from manuscript III and IV, showed a combination of initial stress response, decrease in potential fungal activity and grazing of bacteria by protozoa as the active layer thawed. This may indicate that the degradation of organic carbon from these soil systems is delayed. Finally manuscript V investigated the turnover time of bacterial 16S transcripts in soil at different temperatures. It was estimated that the half-life of rRNA transcripts was 7.1 and 25 days when incubated at 20 °C and 5 °C, respectively.