Composition of Stable Carbon Isotopes in Organic Matter of Cambisols of the Eastern Sayan Foothills

Assessing the variability of stable carbon isotope composition in Cambisol organic matter is important for understanding the response of forest soils to environmental changes. The studies were carried out in the foothills of the northeastern macroslope of the Eastern Sayan Ridge. For the first time, the formation of Cambisols was proved there. Investigated soils are among the isotopically lightest soils in the Baikal region, which is most associated with favorable moistening conditions for the vegetation that forms soil organic matter (δ13С values of the dominant species vary from –32.6 to –27.8‰). Variations in δ13С values from site to site do not exceed 1‰ (–25.81…–26.81‰) for the organic matter of surface soil horizons despite significant differences in the input and subsequent transformation of organic matter. At the same time, a significant soil profile gradient of δ13С values (4–5‰) is registered. The analysis of differences in the intensity of carbon turnover expressed through the slope of the linear regression (β) between δ13C values and log-transformed content of total carbon in the soil, which varies with depth, showed that, most likely, the isotopic depth-profile of the studied Cambisols is formed under the influence of microbial utilization of organic matter, which is manifested having different intensity depending on the composition of organic-rich horizons. The increased intensity of mineralization of labile components of plant material in the upper part of the organic profile of soils with developed litter and organic-accumulative horizons can lead to a noticeable increase in δ13С values and a more pronounced β, in contrast to soils with a predominance of mineral horizons in the organic profile.