Soils Associated with Biotic Activity on Frost Boils in Arctic Alaska

Frost boils occur extensively across arctic tundra ecosystems, and biotic crusts form on the mineral soils exposed in centers of boils. These center areas of the frost boils eventually become completely covered by tundra vegetation. We studied the biogeochemistry of the surface soils (0- to 10-cm depth) on frost boils at nine sites across a soil pH gradient in arctic Alaska. Soils under biotic crusts were compared with adjacent bare and fully vegetated areas within the centers of the same boil. Near the sea coast we found segregation of Na salts to the bare surface areas of boils and concentration of Ca under adjacent crusted areas within the boils. In contrast, inland coastal plain soils with non-acidic tundra showed Ca accumulation under both crusted and vegetated areas within the boils. Nonacidic soils rich in inorganic C were effective at buffering pH changes with organic carbon (OC) accumulations of up to 200 g kg(-1). Soil water-soluble OC (OCws) stocks of nonacidic boil sites correlated well with soil total OC (R-2 = 0.62, p < 0.01), while OCws for boils formed in acidic soils was correlated to total soil N stocks (R-2 = 0.69, p < 0.01), consistent with there being different limitations to soil biological activity for soils across the soil pH gradient. Although there were differences in quantity of accumulated organic matter across the soil pH gradient, soil nutrient pools increased as OC accumulated under crusted and then vegetated soils across all sites.