C-N Isotope Coupling along the Vertical Profiles under Different Land Use in a Typical Karst Area, Guizhou, Southwest China

The soil stable carbon and nitrogen isotopic compositions characterize its fate and identify the different land use. In this study, carbon concentration and isotope component, nitrogen concentration and isotope component, and C/N ratios in soils collected from Puding, southwest of China were determined. The carbon and nitrogen content data range from 7.92% to o.48%, and 0.77% to 0.05%, respectively. Soil δ13C ranged from -25.49‰ to -17‰, soil δ15N varied from 1.11‰ to 9.46‰. The concentrations of SOC and SON decrease with depth along the vertical profiles. In addition, combined the SOC and δ13C or SON and δ15N could obtained the possibility of distinguish the replaced of C3 and C4 plants. However the pattern of distribution in soil organic δ13C is different from that in soil organic δ15N at the subsoil (deeper than 30 cm). With correlation analyses with C/N ratios and δ13C, it reveals that subsoil carbon microbial derived carbon due to root activity.