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%.

Permafrost soils and carbon cycling

“…The northern circumpolar region contains about 30-40 % of the global soil carbon pool to a depth of 3 m, yet the region covers just 15 % of the global land surface and supports only 10-20 % of the global vegetation carbon pool (Jobbágy and Jackson, 2000;McGuire et al, 2009;Hugelius et al, 2014;Köchy et al, 2014). The disproportionate ratio of soil carbon to plant biomass carbon in the permafrost region is due to the slow decomposition rates for organic matter under the low temperatures and often saturated (thus reducing) conditions in these soils (Hobbie et al, 2000;Davidson and Janssens, 2006;Ping et al, 2008bPing et al, , 2010. However, in permafrost soils, other processes, such as crystal and massive ice formation, freeze cracking, freeze jacking, diaparism, and gelifluction can result in deformation and displacement of soil materials within the profile.…”

“…This work led to the creation of the subgroup of "Ruptic-Histic" in the US taxonomic system (Soil Survey Staff, 1975). Later, more detailed pedological studies in Arctic Alaska asserted that cryoturbation is the primary factor controlling the amount of carbon sequestered in the soils of tundra dominated by nonsorted circles Ping et al, 1998Ping et al, , 2008bBockheim and Hinkel, 2007). Thus, the presence/absence of cryoturbated features was adopted as differentia for the Turbel suborder of Gelisols in US taxonomy Tarnocai, 1998, Ahrens et al, 2004) and for the prefix of Cryosols in the WRB (IUSS Working Group WRB, 2014).…”

“…Redistribution of organic matter within the soil profile due to cryoturbation is most common in the Arctic, where patterned ground processes are active -such as sorted and nonsorted circles and ice-wedge polygons (Washburn, 1973;Michaelson et al, 2008;Walker et al, 2008;Kanevisky et al, 2011;Zubrzycki et al, 2013;Ping et al, 2008bPing et al, , 2014. In early studies, SOC stocks were measured only at shallower depths -mostly limited to the rooting zones at depths less than 50 cm, due to logistics (Brown, 1969;Everett and Brown, 1982).…”

“…However, as concerns about global warming increased, this raised fears that the organic carbon stored in permafrost-region soils might become a source of rather than a sink for atmospheric carbon (Oechel et al, 1993). Consequently, a series of studies was conducted in the northern circumpolar regions to explore the depth distribution of stored biogenic carbon in Gelisols (Michaelson et al, 1996Ping et al, 1998Ping et al, , 2008bBockheim and Hinkel, 2007;Bockheim et al, 1999;Tarnocai et al, 2009;Hugelius et al, 2010Hugelius et al, , 2013aStrauss et al, 2012Strauss et al, , 2013. Generally, on gentle to moderate slopes of glaciated uplands, SOM was cryoturbated to depths of mostly 80 to 120 cm.…”

“…But, in the poorly drained valleys or basins among the hilly uplands, thick organic horizons (> 40 cm) can build up due to fen or bog formation, and these soils are classified as Histels (Cryic Histosols) (Ping et al, , 2005a. Ping et al (2008b) measured SOC stores along a northsouth transect through five bioclimatic subzones from the High Arctic to the boreal regions in North America as part of a larger study investigating the interrelationships between patterned ground formation and vegetation zonation . As the patterned ground transitioned from simple frost cracking in the High Arctic to well-formed nonsorted circles in the Low Arctic, the land-cover types changed from polar desert to tundra to shrub tundra, with increased dominance of vascular plants in the south .…”