Contents and factors Influencing Soil Organic Carbon of Three Forest Types in the Lower Reaches of Chishui River

The soil organic carbon, carbon density and the vertical distributions were studied and the influences of the soil nutrients on the soil organic carbon were tested in the Chinese fir forests, masson pine forests and bamboo forests in the lower reaches of Chishui River, Guizhou province. The results showed that the average contents of soil organic carbon in the 0~ 80 cm deep soil profile from large to small in order were in the bamboo forests(15.46 g / kg), Chinese fir forests(13.78 g / kg) and Masson pine forests(9.72 g / kg) with obvious difference between them. The organic carbon density from large to small in order was in the Chinese fir forests(12.87 kg / m2), bamboo forests(11.73 kg / m2) and Masson pine forests(8.21 kg / m2) with obvious difference between them. In all three forest types, the contents of soil organic carbon and the carbon density both deceased gradually with the deepening of the soil profiles. The contents of organic carbon were the highest in the 0~10 cm deep soil profile, 1.47 to 2.30 times as many as the average contents of organic carbon of the whole soil profile. The organic carbon density in the 0 ~20 cm deep soil profile accounted for 31.71% to 47.83% that of the whole soil profile, obviously higher than that in any other soil profile. The soil organic carbon and the carbon density were considerably more fixed on the surface of the soil, which required for strengthening ecological protection to avoid human interventions and reduce the risks of soil and water erosion. The dominant factor influencing the contents of the soil organic carbon was the hydrolyzable nitrogen in the Chinese fir forests and the Moso bamboo forests, while that was the available phosphorus in the Masson pine forests.