Importance of lichen and moss litters to soil carbon storage in black spruce forests on permafrost

Abstract Aims Climate warming is predicted to increase permafrost degradation and soil carbon (C) loss, while changes in microrelief and vegetation cover can also influence soil C storage at local scale. Black spruce forests develop lichen/moss-covered organic mounds on permafrost. Recalcitrance of lichen and moss litters, as well as cold climate, is hypothesized to increase C storage in hummocky soils. Methods We compared the decomposition rates of lichen and moss litters, spruce root litter, and cellulose at hummocky clayey soils, non-hummocky clayey soils, and non-hummocky sandy soils in northwest Canadian subarctic. Results Lichen/moss-covered hummocky clayey soils display greater C stocks than non-hummocky clayey and sandy soils. Lichen and moss litters decomposed more slowly than did spruce root litter and cellulose. Recalcitrant litter inputs of lichen and moss contribute to greater C stocks of hummocky clayey soils, compared to non-hummocky clayey and sandy soils. Lower temperature dependency of lichen and moss litter decomposition, compared to vascular plant litter, suggests stronger resistance of lichen and moss litters to decomposition. Conclusion Permafrost degradation by climate warming would reduce hummocky microrelief covered by lichen and moss, major contributors to soil C, and decrease the high potential for C storage of black spruce forests on permafrost.