Effects of landscape age on soil organic matter processing in northern Alaska

Much of the previous research on arctic soil biogeochemistry has focused largely on the effects of climate, organisms, and relief rather than on geologic factors. However, a few studies of limited scope suggest that biogeochemical cycling in tundra soils may be significantly affected by variation in glacial history. To determine if variation in landscape age-related differences in geochemistry influence rates of organic matter decomposition in tundra soils, we conducted soil analyses and a 5-mo soil incubation study across a chronosequence of landscape ages in northern Alaska. Our results indicate that there were landscape-age related controls on microbial activity, with higher microbial biomass, rates of respiration, and production of dissolved organic C (DOC) and N (DON) in soils from the older landscape ages than in soils from younger, less weathered landscapes. This biological boundary corresponded to a chemical boundary, as older soils had lower pH (4.5-5 vs. 6.5) and exchangeablecation concentrations than the youngest soils. There were no differences among landscape ages in total C stocks in organic soils; however, total N stocks in the organic soil decreased with increasing landscape age. Differences among landscape ages in microbial activity due to geochemical variation may have important consequences for tundra C budgets because differences in soil pH and cation content exist throughout the circumpolar region.