Surface Soil Organic Matter Qualities of Three Distinct Canadian Arctic Sites

Cryosolic soils store large amounts of carbon (C) because soil organic matter (SUM) decomposition is slower than plant growth. The response of arctic SOM to climate change is likely to depend not only on temperature, but also upon complex interactions between soil properties and SOM chemistry. We hypothesized that organic surface soils (>17% carbon) have more labile SUM than mineral surface soils (<17% carbon). Furthermore, we hypothesized that high arctic soils have more labile SUM than soils from the Low Arctic and subarctic. This study was conducted in 3 arctic ecosystems: subarctic (Churchill, Manitoba; n = 138), Low Arctic (Daring Lake, Northwest Territories; n = 60), and High Arctic (Truelove Lowlands, Nunavut; n = 54). The 0-10 cm depth of several different Cryosolic soils was sampled. The results from density fractionation and solid-state C-13 cross polarization and magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy showed that organic surface soils contained relatively more labile C than mineral surface soils. Organic soils contained about 13% more O-Alkyl-C and 30% less Aromatic-C than mineral soils. Furthermore, for Churchill, Daring Lake, and Truelove organic soils, 53, 73, and 20% of the C was included in the light fraction of SUM [LF (LF < 1.55 g mL(-1))], whereas 24, 19, and 14% of the C was included in the LF of mineral soils, respectively. Organic surface soils of subarctic and low arctic sites contained relatively more labile C than the high arctic site. Results showed that the subarctic and low arctic sites store about 15% more O-alkyl-C and 35% less Aromatic-C than high arctic organic soils (P < 0.001).