Evaluating carbon dynamics and microbial activity in arctic soils under warmer temperatures

• Published in: Canadian Journal of Soil Science
• Main Authors: Oelbermann, Maren, English, Michael, Schiff, Sherry L
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2008
• Subjects: Arctic; Daring Lake; Northwest Territories; Climate change; permafrost
• Online Access: http://dx.doi.org/10.4141/cjss07060; http://www.nrcresearchpress.com/doi/pdf/10.4141/CJSS07060

A large portion of carbon (C) is stored in the world’s soils, including those of peatlands, wetlands and permafrost. However, there is disagreement regarding the effects of climate change on the rate of organic matter decomposition in permafrost soils of the arctic. In this study it was hypothesized that soil exposed to a higher ambient temperature would have a greater flux of CO 2 as well as a change in the metabolic diversity of culturable soil microorganisms. To evaluate this hypothesis we determined soil C dynamics, soil microbial respiration and activity, and 13 C and 15 N fractionation in laboratory incubations (at 14 and 21°C) for an organic-rich soil (Mesic Organic Cryosol) and a mineral soil (Turbic Cryosol) collected at the Daring Lake Research Station in Canada’s Northwest Territories. Soil organic C (SOC) and nitrogen (N) stocks (g m -2 ) and concentration (%) were significantly different (P < 0.05) between soil horizons for both soil types. Stable isotope analysis showed a significant enrichment in δ 13 C and δ 15 N with depth and a depletion in δ 13 C and δ 15 N with increasing SOC and N concentration. In laboratory incubations, microbial respiration showed three distinct phases of decomposition: a phase with a rapidly increasing rate of respiration (phase 1), a phase in which respiration reached a peak midway through the incubation (phase 2), and a phase in the latter part of the incubation in which respiration stabilized at a lower flux than that of the first phase (phase 3). Fluxes of CO 2 were significantly greater at 21°C than at 14°C. The δ 13 C of the evolved CO 2 became significantly enriched with time with the greatest enrichment occurring in phase 2 of the incubation. Soil microbial activity, as measured using Biolog Ecoplates TM , showed a significantly greater average well color development, richness, and Shannon index at 21°C; again the greatest change occurred in phase 2 of the incubation. Principal component analysis (PCA) of the Biolog data also showed a change in the distinct ...