Effects of hummocky microrelief on organic carbon stocks of permafrost-affected soils in the forest-tundra of northwest Canada

抄録

We analyzed the effects of hummocky microrelief on soil organic carbon (SOC) stocks of permafrost-affected soils (or Gelisols) in northern Canada. We compared the microrelief and SOC stocks in black spruce forests on clayey and sandy sediments in Mackenzie upland area. Hummock formation was maximal in clayey soils at the middle position of upland with a shallow permafrost table, where the soils were seasonally flooded by spring snowmelt and summer permafrost thawing. The higher water content due to poorer drainage, rolling permafrost table, and freeze-thaw cycles can promote greater hummock formation in the clayey soils. The soils on the strongly-developed hummocky microrelief have greater SOC stocks than those on weakly-developed microrelief. This can be explained by the retardation of microbial decomposition by summer flooding and accumulation of recalcitrant lichen and moss litters on strongly-developed hummocky microrelief. The concentration of oxalate-extractable short-range-order iron oxides in soils, which are enriched through redox cycles by seasonal flooding, can serve as a rough proxy for predicting local variation in SOC stocks in the mineral soils in black spruce forests on permafrost.