Carbon and nitrogen stable isotopes in forest soils of Siberia
The labeled atoms of carbon and nitrogen are widely used in biology, biochemistry, and soil science. Both radioactive (14C) and stable (12C, 13C,15N) isotopes are used as such labels. Recently, an increase in mass spec-trometry sensitivity made it possible to study natural ratios of carbon (13C/12C) and nitrogen (15N/14N) stableisotopes in various biological objects. Since most bio-logical processes discriminate isotopes, i.e., use lighterisotopes for fermentative reactions  and leave heavier isotopes in substrate, the study of isotopic com-positions of various habitats of organisms yields infor-mation on intensity and direction of biological pro-cesses. However, the interpretation of carbon and nitro-gen isotopic compositions in complex objects, such as soil, meets difficulties because of the far too great num-ber of factors that control isotope fractionation [2, 6,11, 13]. The forest soils of the Yenisei meridian signif-icantly vary in terms of environmental factors, and thisvariability opens up possibilities to reveal the most important factors that determine carbon and nitrogen isotopic compositions of soils. In this work, the distri-bution of carbon and nitrogen isotopes in the forestsoils of the Yenisei region of Siberia was investigated for the first time. It has been shown that these isotopes are good indicators of (a) the intensity of organic matter (OM) mineralization, (b) the contribution of nitrogen fixation to the nitrogen status of ecosystems, and (c) the
provision of ecosystems with moisture.