Comparison of soil active organic carbon fractions in different vegetation zones in purple-soil of hill slope

To explore the effect of vegetation restoration on soil carbon cycle and fractions of soil organic carbon pool on purple-soil hill slope in Hengyang City of Hunan Province, China was selected. The soil samples of 0 10 and 10 20 cm soil layers under three types of vegetation, i.e., grassland zone (GZ), grassland-forest zone (GFZ) and forest zone (FZ). The dynamics of soil active organic carbon (SAOC) fractions to provide theory basis for the influence of soil carbon cycle and different vegetation zones on the fractions of organic carbon pool and its stability. Results show: Microbial biomass carbon and easily oxidizable organic carbon exhibited a decreasing pattern: FZ, GZ, GFZ (p < 0.05); Dissolved organic carbon exhibited a decreasing pattern: FZ, GFZ, GZ (p < 0.05); Light fraction organic carbon was the highest in FZ (p < 0.05), and the second in GZ and GFZ; The availability of active organic carbon in 0 10 cm soil layer was higher than that of 10 20 cm soil layer (p < 0.05); In comparison with GFZ, the herb in GZ could increase the contents of active organic carbon. Introduction Soil active organic carbon (SAOC), the active part of soil organic carbon (SOC), is considered as the organic carbon of high availability which is easy to be decomposed and mineralized by microorganism and directly supply nutrients to plants (Vieira et al. 2007). Some workers believe that the content of SOC is the result of the balance between the accumulation of organic carbon and its mineralization decomposition. Thus it cannot appropriately reflect the change in soil quality (Dodla et al. 2012). Although SAOC accounts for only a small part of the total SOC, it plays an important role in maintaining land productivity and reflecting the soil carbon storage variation, and is more sensitive to the micro-environment change of various vegetation than SOC. SAOC directly takes part in the process of soil biochemical conversion, and also acts as the energy for soil microbial activities and the driving force of soil nutrients (Wander et al. 1994). It reflects better availability of SOC and the soil quality (Boone et al. 1998, Wang et al. 2005). So, the investigation of SAOC is an important element for the research of dynamics and regulation mechanism of vegetation-soil carbon pool. Purple-soil hilly slope land, covering an area of 1.625×10 hm, is one of the poorest areas in ecological environment in Hengyang city of Hunan Province, and also a typical area frequently hit by ecological disasters. The purple soil, with a short period of development, is extremely vulnerable to water erosion and infertile. Together with its strong heat absorptivity for its dark color, intensive evaporation for the heat on ground in summer, regional unbalanced allocation of water and heat resources and irrational development, the region has been faced with problems like sparse vegetation, severe water and soil erosion and seasonal draughts for a long time. The deteriorated ecological environment has seriously curbed the local rural economic development. Author for correspondence: <yangning8787@sina.com>.