Carbon and nitrogen stable isotopes in forest soils of Siberia

Abstract

N) stableisotopes in various biological objects. Since most bio-logical processes discriminate isotopes, i.e., use lighterisotopes for fermentative reactions [10] and leaveheavier 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 assoil, 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 mostimportant factors that determine carbon and nitrogenisotopic compositions of soils. In this work, the distri-bution of carbon and nitrogen isotopes in the forestsoils of the Yenisei region of Siberia was investigatedfor the first time. It has been shown that these isotopesare good indicators of (a) the intensity of organic matter(OM) mineralization, (b) the contribution of nitrogenfixation to the nitrogen status of ecosystems, and (c) theprovision of ecosystems with moisture.The soil samples were taken in August 2003 fromtest sites of the Siberian IGBP transect set up by theSukachev Institute of Forestry, Siberian Division, Rus-sian Academy of Sciences within the framework of theInternational Geosphere–Biosphere Program (IGBP) [7].The sections were set up in the northern taiga forests(lower reaches of the Nizhnyaya Tunguska River) andat the boundary between the southern taiga and the for-est–steppe zone (Pogorel’sky Bor Station). Thixotropiccryosol (kriozem) and brown taiga soil (podbur) werestudied in the northern taiga. Two sections of gray for-est soil in the birch and larch types of forest were stud-ied at the boundary between the southern taiga and for-est–steppe zones. The soil types chosen for the investi-gation are the most typical of the northern taiga andforest–steppe zones. The ecological and genetic charac-teristics of these soils are given in [9, 10]. Some chem-ical properties of the soils are presented in the table.Three soil samples were taken from each soil horizon,followed by an average composite sample. The sampleswere dried outdoors and screened through a sieve of 1mm. Carbon and nitrogen concentrations and isotoperatios (