Vast amounts of carbon are bound in both active layer and permafrost soils in the Arctic. As a consequence of climate warming, the depth of the active layer is increasing in size and permafrost soils are thawing. We hypothesize that pulses of biogenic volatile organic compounds are released from the near-surface active layer during spring, and during late summer season from thawing permafrost, while the subsequent biogeochemical processes occurring in thawed soils also lead to emissions. Biogenic volatile organic compounds are reactive gases that have both negative and positive climate forcing impacts when introduced to the Arctic atmosphere, and the knowledge of their emission magnitude and pattern is necessary to construct reliable climate models. However, it is unclear how different ecosystems and environmental factors such as drainage conditions upon permafrost thaw affect the emission and compound composition. Here we show that incubations of frozen B horizon of the active layer and permafrost soils collected from a High Arctic heath and fen release a range of biogenic volatile organic compounds upon thaw and during subsequent incubation experiments at temperatures of 10 degrees C and 20 degrees C. Meltwater drainage in the fen soils increased emission rates nine times, while having no effect in the drier heath soils. Emissions generally increased with temperature, and emission profiles for the fen soils were dominated by benzenoids and alkanes, while benzenoids, ketones, and alcohols dominated in heath soils. Our results emphasize that future changes affecting the drainage conditions of the Arctic tundra will have a large influence on volatile emissions from thawing permafrost soils - particularly in wetland/fen areas.

The forest-tundra interface is the world's largest ecotone, and is globally important due to its biodiversity, climatic sensitivity, and natural resources. The ecological communities which characterize this ecotone, and which provide local and global ecosystem services, are affected by environmental variation at multiple scales. We explored correlations between environmental variables and macroinvertebrate and soil prokaryote communities in the forest-tundra ecotone of the Yukon, Canada. We found that each tussock tundra site possessed a distinct community of macroinvertebrates and prokaryotes, and therefore represented a unique contribution to regional biodiversity. Prokaryote diversity increased with active layer depth, which could be an effect of temperature, or could be evidence of a species-area effect. Prokaryote diversity decreased with lichen cover, which could be due to antimicrobial properties of lichen. The macroinvertebrate community composition was affected by proximity to a human disturbance, the Dempster Highway. Both macroinvertebrate and prokaryote community compositions changed along the latitudinal transect, as the biome transitioned from taiga to tundra. We also found that the abundance of carnivores relative to herbivores decreased with latitude, which adds to recent evidence that predation decreases with latitude. Our survey yielded new insights about how macro- and microorganisms vary together and independently in relation to environmental variables at multiple scales in a forest-tundra ecotone.