Description: The microbial process of methane (CH4) production during the back-freezing of permafrost soils in autumn and the future fate of produced CH4 in the thawing phase of the following spring are not well understood. Long-term CH4 flux studies in the Lena Delta (Siberia) indicate that back-stored CH4 adds to the emission of newly-produced CH4 at the beginning of the vegetation period. Further field analysis shows that microbial CH4 production already occurs at in situ temperatures of around 1°C in the bottom layer of the soil. Therefore, a permafrost microcosm was developed to simulate the influence of the annual freezing-thawing cycles on the CH4 fluxes in the active layer of permafrost soils. Two cryostats ensure independent freezing and thawing the top and the bottom of the microcosm to simulate different field conditions. The CH4 concentration (Rhizon soil moisture samplers), the soil temperature (film platinum resistance temperature detectors [RTDs]) and the soil water content (time domain reflectometry) are analysed in different depths of the microcosm during the simulation in addition to the concentration of emitted CH4 in the headspace of the microcosm. The data obtained contribute to the understanding of microbial processes and CH4 fluxes in permafrost environments in the autumn and early winter.

Description: The bacterial community composition of the active layer (0–45 cm) of a permafrost-affected tundra soil was analysed by fluorescence in situ hybridisation (FISH). Arctic tundra soils contain large amounts of organic carbon, accumulated in thick soil layers and are known as a major sink of atmospheric CO2. These soils are totally frozen throughout the year and only a thin active layer is unfrozen and shows biological activity during the short summer. To improve the understanding of how the carbon fluxes in the active layer are controlled, detailed analysis of composition, functionality and interaction of soil microorganisms was done. The FISH analyses of the active layer showed large variations in absolute cell numbers and in the composition of the active microbial community between the different horizons, which is caused by the different environmental conditions (e.g., soil temperature, amount of organic matter, aeration) in this vertically structured ecosystem. Universal protein stain 5-(4,6-dichlorotriazin-2-yl)aminofluorescein (DTAF) showed an exponential decrease of total cell counts from the top to the bottom of the active layer (2.3 × 109–1.2 × 108 cells per gram dry soil). Using FISH, up to 59% of the DTAF-detected cells could be detected in the surface horizon, and up to 84% of these FISH-detected cells could be affiliated to a known phylogenetic group. The amount of FISH-detectable cells decreased with increasing depth and so did the diversity of ascertained phylogenetic groups.

Description: The soil characteristics and the bacterial community of the active layer (0-45 cm) of a permafrost affected tundra soil were analysed. The composition of the bacterial community was investigated by fluorescence in situ hybridisation (FISH) while BIOLOG Ecoplates were used to characterize microbial communities by determining the ability of the communities to oxidize various carbon sources. Arctic tundra soils contain large amounts of organic carbon, accumulated in thick soil layers and are known as a major sink of atmospheric CO2. These soils are totally frozen throughout the year and only a thin active layer is unfrozen and shows biological activity during the short summer. To improve the understanding of how the carbon fluxes in the active layer are controlled, detailed analysis of composition, functionality and interaction of soil microorganisms was done. The FISH analyses of the active layer showed large variations in absolute cell numbers and in the composition of the active microbial community between the different horizons, which is caused by the different environmental conditions (e.g. soil temperature, amount of organic matter, aeration) in this vertically structured ecosystem. Results obtained by universal protein stain 5-(4,6-dichlorotriazin-2-yl)aminofluorescein (DTAF) showed an exponential decrease of total cell counts from the top to the bottom of the active layer (2.3 × 109 to 1.2 × 108 cells per g dry soil). By using FISH, up to 59% of the DTAF-detected cells could be detected in the surface horizon, and up to 84% of these FISH-detected cells could be affiliated to a known phylogenetic group. With increasing depth the amount of FISH-detectable cells decreased as well as the diversity of ascertained phylogenetic groups. The turnover of substrates offered on the BIOLOG Ecoplates was slower and less complete in the deeper soil horizons. Especially in the upper 5 cm the turnover of some of the polymeric substances and some carbohydrates was much better than in deeper parts of the soil. The interaction of important soil parameters (water table, nutrient availability, roots) leads to a larger and more diverse community in the upper 20 cm of the soil, which again cause a faster and more complete turnover in this part of the active layer.