Abstract: In this study, we investigated the bulk density (BD), water content (WC), organic carbon (SOC), and stable carbon isotope composition (δ¹³C) of soils collected from different successional stages of steppe vegetation in Yunwu Mountain, Ningxia Province. The δ¹³C values of the dominant plants in the vegetation were also analyzed. Our aims were to compare the differences in these variables between different vegetation types and to understand the related environmental information. Results showed that the SOC in the surface layer (0-10 cm layer) was 71.7 g·kg^-1 in shrub land, being significantly higher than that in grassland (54.6 g·kg^-1). The SOC for the 0-20 cm layer in shrub land accounted for 58.1% of the SOC above 1 m, whereas in grassland the SOC in the 0-40 cm layer only accounted for 34.1% of the SOC above 1 m. The shortterm vegetation succession had a significant influence on the δ¹³C values of SOC in the 0-20 cm layer, particularly in the 0-10 cm layer. The vegetation succession from grassland to shrub land led to a negative shift of 1.4‰ in δ¹³C values, but there was no significant change below soil depth of 30 cm. Therefore, δ¹³C might be a useful tool for studying the changes of soil carbon stock and carbon cycle during shortterm vegetation succession of C₃ plants. The δ¹³C values became less negative from leaves to roots, with the deviation being 2.2‰ for shrubs and 1.9‰ for grass. Moreover, for plant roots from 0 to 40 cm depth, the δ¹³C values changed from -28.15‰ to -26.11‰ in shrub land and from -27.08‰ to -27.57‰ in grassland.

Key words: nitrogen efficiency, nitrogen fertilizer, management mode, light use efficiency