Dynamic Change of Soil Organic Carbon Density and Microbial Biomass Carbon during Natural Revegetation

Soil carbon density and soil microbial biomass carbon (SMBC) were studied based on the different chronosequence sites during the revegetation process on loess hilly-gully area in southern Ningxia. The results showed that soil organic carbon (SOC) and microbial biomass carbon in the soil profile were 0-5 cm soil layer5-10 cm soil layer10-20 cm soil layer. There were significant differences among layers of SOC and SMBC. During natural revegetation,the enrichment effects of SOC and SMBC in the soil surface were obvious. SOC and SMBC in each profile were logarithmically increased with vegetation restoration years. SOC and SMBC were greatly increased during 0~23 years of revegetation,but the change of SOC and SMBC were small during 23~75 years. In the 0-5 cm soil profile,SOC and SMBC increased 4.81% and 6.96% per year within 23 years respectively,but only 0.25% per year during 23 to 75 years. Soil microbial quotient (SMQ) changed in 2.113~4.375. The turnover rate of soil organic carbon within vegetation restoration of 12 years was faster than those 12 to 75 revegetation years,the accumulation of SOC was main in the surface. By correlation analysis,SOC was significantly positive correlated with SMBC (p0.01),it can explain that SMQ was more suit to represent SMBC than SOC during natural revegetation. Compared with the farmland,soil organic carbon density (SOCD) increased 85.23% within 23 years,but only 6.60% during 23 to 75 years of revegetation. The result showed vegetation natural restoration can improve soil organic carbon reservation,and promote soil carbon fixation.