Variations in the Stable Carbon Isotopic Composition of Soil Organic Matter in Mountain Depressions of the Cis-Baikal Region

Depth-profile and spatial variations of the stable carbon isotopic composition of soil organic matter is analyzed to identify the main factors that determine the dynamics of organic carbon in the mountain-depression environments of the Baikal Region. Soil organic matter is characterized by δ13С values from –29.6 to –24.9‰. Variations in δ13C in the altitudinal profile correlate well with changes in landscapes and reflect the influence of climatic factors on 13C discrimination during photosynthesis of C3 plants. Soils of subalpine and steppe landscapes are characterized by the heaviest stable carbon isotopic composition. Taiga soils are depleted of the isotopic composition by 13C. To compare the soil carbon turnover intensity, δ13C values were linearly regressed against log-transformed carbon contents yielding absolute values of these slopes (β). The distribution of β values in the altitudinal profile suggests a reduced intensity of carbon turnover in the soils of steppes and the subalpine belt due to insufficient moisture and temperature, respectively. Under the taiga conditions characterized by a more favorable ratio of temperatures and humidity, the dynamics of soil organic matter is mainly controlled by the litter quality and the nitrogen availability.