Effect of local environmental factors on the stable carbon isotopic composition of soils in Olkhon region

Abstract

We studied spatial and vertical variation in stable carbon isotopic composition of soil organic matter in the central part of the western coast of Lake Baikal. This area is characterized by a contrasting landscape structure and significant climatic variability, which has a strong effect on the soil stable carbon isotopic composition. The δ13С values of organic matter and litter are in the range from –27,93 to –18,19 ‰ and indicate the predominance of C3-pathway vegetation. However, in the steppe landscapes, single plants with C4 and CAM photosynthesis were noted. The δ13С values increase in the direction from the forest soils of the foothills of the Primorsky Range to the steppe soils of the Pre-Olkhon Plateau. This trend reflects a decrease in humidity which is the main limiting factor in the soil development in the Olkhon region. Insufficient moisture determines the stable carbon isotopic composition of soil organic matter through 13C discrimination in plant tissues. Regardless of the soil-forming conditions the soils of the study area are characterized by a decrease in δ13С values with depth. However, the degree of manifestation of such a gradient is determined by local combinations of environmental factors. More intensive carbon turnover is assumed in the soils of coastal landscapes, negative landforms, and on the slopes of northwestern exposures based on the differences of soils in terms of the regression between log-transformed carbon content and δ13C depth-profile (β). Under such conditions the influence of air masses from Lake Baikal causes a significantly lower drying of the soil profile in summer and provides a more favorable water and temperature regime for microbiological activity. At the same time, β variations are not accompanied by significant fluctuations in C:N and pH values, which may indicate an insignificant role of edaphic factors and overlapping of their influence by the effect of moisture deficiency on the carbon turnover intensity in the soils of the Olkhon region.