Carbon Stores and Biogeochemical Properties of Soils under Black Spruce Forest, Alaska

Abstract

Fifty‐two soils under black spruce [Picea mariana (Mill.) Britton et al.]‐dominated forest communities were examined and assessed for their organic C (OC) stores in relation to soil characteristics. Study sites were located on a variety of parent materials, landscape positions, and drainage conditions. Results indicate that soils at most sites were weakly developed, commonly with organic (O) horizons ranging from 3 to 39 cm (≥100 cm occasionally). Organic C stores tended to increase as drainage changed from somewhat excessive and well to very poorly drained (average to 1 m: 12.6–50.9 kg OC m−2, respectively). The lowest OC store for an individual site was 7.1 kg OC m−2 in a well‐drained soil on an outwash plain and the highest was 109 kg C m−2 in a very poorly drained soil. Surface organic horizons contained 13 to 100% of the total pedon OC stores. In Gelisols, permafrost sequestered an average of 9, 19, and 39% of SOC stores for the somewhat poorly, poorly, and very poorly drained soils, respectively. The presence of permafrost in poorly drained sites increased average OC stores from 27.8 to 50.1 kg OC m−2 over those without permafrost. Soil bulk density, cation exchange capacity, and extractable acidity assessed in relation to OC stores of genetic horizons illustrate the significant impact of OC on soil properties. In previous ecological studies in Alaska, OC was determined for only the surface horizons; our data suggest that such shallow sampling may underestimate total OC stores by an average of 26% and up to 68%.