Understanding the variability of stable carbon isotopic composition of organic matter in Cambisols, one of the most widespread soils in the temperate zone, can shed light on the response of forest soils to changes in environmental conditions. 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 here was established. Investigated soils are one of the isotopically lightest soils of 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‰). The 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, there is a significant intrasoil gradient of δ13С values (4–5‰). An 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 isotope profile of the studied Cambisols is formed under the influence of microbial utilization of organic matter, which manifests itself with 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.
