VERTICAL PATTERNS OF STABLE CARBON ISOTOPE IN SOILS AND PARTICLE-SIZE FRACTIONS OF KARST AREAS, SOUTHWEST CHINA

Abstract

Taking limestone soil and yellow soil, the two major soil types in karst areas as examples, analyzing stable carbon isotope composition (δ13C value) of soil organic matter (SOM) in bulk soils and particle-size fractions of four soil profiles under three vegetable forms, the following results are reached: in the limestone soil profile, soil organic carbon contents are all above 1.0%, the highest value is 7.1% in the surface soil; however, they are between 0.3% and 4.6% in the three yellow soil profiles. From the surface to the bottom of the soil profiles, the variation of δ13C value of soil organic carbon for limestone soil profile is only between −24.1‰ and −23.0‰, however, it’s between −24.8‰ and −21.1‰ for yellow soil profiles. The variation range of δ13C value of soil organic carbon associated with particle-size separates is slight for limestone soil but is considerable for yellow soil. The contrast research indicates that the changes between the contents and the δ13C value of soil organic carbon with depth are complex. The vertical patterns of stable carbon isotope in soil organic matter have a distinct regional characteristic in karst areas.