Soil carbon inventories and carbon-13 on a latitude transect in Siberia

Abstract

We present soil organic carbon (SOC) inventories and carbon isotope compositions from over 900 samples collected in areas of minimally disturbed mature vegetation on freely drained soils (excluding peatlands) on a 1000 km transect along the Yennisey River, central Siberia. Carbon inventories over 0-30 cm depth range widely from 1.71 to 7.05 kg m-2. While an effect of changing climate or vegetation along the transect cannot be ruled out, the observed differences in SOC inventories are largely the result of variations in mineral soil texture, with inventories in fine-textured soils being approximately double those in coarse-textured soils. The δ13C values of SOC in the 0-5 cm interval ranged from -26.3 to -28.0‰, with δ13C values for the 5-30 cm interval being 0.9 ± 0.8‰ (1σ) enriched in 13C relative to the 0-5 cm samples. The average δ13C value for the 0-5 cm interval for all samples was -27.1 ± 0.6‰ (1σ) and for the full 0-30 cm interval the average was -26.5 ± 0.5‰ (1σ). In general, δ13C values were higher in coarse-textured soils and lower in fine-textured soils. The results of detailed sampling of soils in Pinus sylvestris forest growing on sand near the Zotino flux tower suggest an SOC inventory in these soils of 2.22 ± 0.35 kg m-2 over 30 cm and an average δ13C value of -26.3 ± 0.2‰ over the 0-5 cm depth interval and -25.9 ± 0.3‰ over 0-30 cm. Recent burning had no effect on SOC inventories, but clearing has led to an average 25% decrease on SOC inventories from 0-30 cm over 12 yr. Neither burning nor clearing had a discernible effect on the δ13C value of SOC.