Abstract: To investigate the impact of short-term vegetation replacement on the distribution of organic carbon in soil and the mechanism of soil carbon cycle, five types of 0-110 cm mountain soil profiles with Quercus trees, shrubs, grass alterations are collected in Qujing, Yunnan Province, China. Each type of soil profile is divided into 6 layers. Stable carbon isotope ratios (δ¹³C values), total organic carbon (TOC) data and carbon density are measured. Results show that: (1) Changes of δ¹³C values after shrubs replaced by Quercus trees and grass are between 2.28‰ and 5.08‰. (2) Vegetation replacement has the greatest impact on ¹³C in SOM (soil organic matter) in the 0-10 cm soil layer. δ¹³C value in the soil layer of 30-50 cm depth is not sensitive to vegetation replacement, thus the leached layer can serve as a reference profile. (3) Short-term vegetation replacements (around 10 years) significantly influence δ¹³C values in the 0-30 cm soil layer. In the 0~50 cm soil layer, enrichment of ¹³C decreases as the depth increases. In addition, δ¹³C values have negative correlation with TOC. Change of atmospheric δ¹³C is not related to ¹³C enrichment in the 0-50 cm soil layer in the forest. (4) Soil organic carbon density in the 0-30 cm layer has changed by 2.30 kg/m² and -1.00 kg/m² in 10 years after replacement of shrub vegetation by oak plantings and herbaceous vegetation, respectively. (5) Planted oak forest has significant impact on short-term soil carbon diversity and storage increase. In 10 years after the change from shrubs to planted oaks, the annual carbon density has increased by 0.23 kg/m². This paper concludes that δ¹³C can be used to distinguish C3 from C4, and even among the different C3 plant (such as arbor, shrubs and herbaceous) changes, hence widely used in the study of soil carbon storage turnover and carbon cycle.

Key words: ¹³C enrichment, carbon density, soil profile, stable carbon isotope, vegetation replacement