Abstract: Soil samples were collected from the Eucalyptus  plantations in the north, east, and west Guangdong and Pearl River Delta region to study their organic carbon content and density, and the main factors affecting the organic carbon density. In the plantations, the soil organic carbon content and density in A and B horizons were significantly different, with the values of (23.94±2.97) g·kg^-1and (9.68±1.05) g·kg^-1, and (27.64±7.72) t·hm^-2 and (108.36±9.37) t·hm^-2, respectively. In 0-50 cm soil layer, the organic carbon density was 66.72±6.53 t·hm^-2, being slightly higher than that in Masson pine and Chinese fir plantations in Guangdong. In both A and B horizons of Eucalyptu plantations, soil organic carbon density was significantly positively correlated with altitude, soil total porosity, capillary porosity, capillary moisture capacity, and total nitrogen content. Soil capillary porosity, capillary moisture capacity, and pH value were the main factors affecting the soil organic carbon density.

Key words: Eucalyptus plantation, soil organic carbon, soil organic carbon density, Guangdong Province, intensive management, Phyllostachys heterocycla stand, N₂fixing bacteria, denaturing gradientgel electrophoresis (DGGE), real-time quantitative PCR.