Composition and content of soil organic carbon in Pinus massoniana pure forest in the Three Gorges Reservoir Area of central China.

Taking Pinus massoniana pure forest and P. massoniana-Quercus fabri mixed forest in Ruxi River Watershed in the Three Gorges Reservoir Area of central China as the research objects, we compared the soil organic carbon and soil respiration intensity of the two kinds of P. massoniana forests. The results showed that the content of total organic carbon, soil microbial biomass carbon (SMBC), readily oxidized organic carbon (ROOC) and water soluble organic carbon (WSOC) in three soil layers (0 -20 cm,20 - 40 cm,40 -60 cm) under P. massoniana-Q. fabri mixed forest were all significantly higher than that of P. massoniana pure forest. The soil respiration rates in each soil layer of the mixed forest were respectively 18.4%, 14.7% and 17.3% higher than that of pure forest, while the allocation proportion of CO2-C released by soil respiration in total organic carbon per day under mixed forest was lower than that of pure forest on the whole. Moreover, there was a significant correlation between soil organic carbon and soil respiration rate in both forest stands. Accordingly, compared with P. massoniana pure forest, the soil of P. massoniana-Q. fabri mixed forest has higher organic carbon storage, and demonstrates stronger carbon sequestration capacity.