Abstract: Soil organic carbon content plays an important role in the global ecosystem carbon stock revolution. By space replacing time series method, we chose two types of forests of mixed broadleaved Korean pine original forest and Betula costata secondary forest to measure the soil organic carbon(SOC) stock, soil nitrogen(TN) content, microbial biomass carbon(MBC) and other soil chemistry and physical properties. The SOC, TN, MBC contents are gradually decreased with the increase of the depth of soil layer, and finally to a stable value. On the contrary, the soil bulk density increases with the increase of depth of the soil layer. There is no significant difference in 0-10 cm soil layer’s SOC,TN content and 10-20 cm soil layer at original forest, but there are significant relations in e two soil layers at secondary forest. The soil organic carbon densities(SOCD) of original forest and secondary forest are 21.46 and 21.3 kg·m^-2, respectively. There is no significant difference between two forest types. The mean soil organic carbon contents of original forest and secondary forest are 35.79 and 28.6 g·kg^-1, respectively. Soil total nitrogen contents of original forest and secondary forest are 2.86 and 1.83 g·kg^-1, respectively. The liner correlation of microbial biomass carbon and soil organic carbon in secondary forest is higher than original forest. The soil fertility of original forest is more than secondary forest. It is better to plant mixed coniferous with pine species in the secondary forest, and have appropriate thinning in original forest to balance the underground carbon system.

Key words: soil carbon stock, soil microbial biomass carbon, soil organic carbon, Betula costata secondary forest, mixed broadleaved korean pine original forest