Assessing patterns and biogeochemical impacts of shrubification in sedge fens of the Hudson Bay subarctic tundra

Abstract

Mean annual air temperatures in Arctic regions have increased by about 2–3°C over the past 50 years. As a result, the abundance and maximum height of woody shrub species has increased (shrubification) at sites around the circumpolar Arctic. This paper examines the extent and impact of shrubification on relevant nutrient cycling, soil microbial community and GHG production potential at a fen environment in the Hudson Bay Lowlands near Churchill, MB. Greening during 1984-2017 was analyzed using Google Earth Engine, a 10-year litterbag study was conducted to compare nutrient release patterns between a sedge and shrub dominated site, soil microbial DNA was extracted from sites and compared, and active layer samples were incubated to determine potential GHG production. We found that greening was extensive in the area, methane production was lower in soils from shrub-dominated sites and shrub litters decomposed significantly slower than sedge litters in the first year. These results suggest that it is unlikely that permafrost is sustainable where shrubs encroach, yet the effects of permafrost thaw on carbon cycling could be in part offset by lower microbial methane production associated with shrubs in near surface soils.