Abstract: In order to understand the effects of soil moisture  on  organic carbon (OC) mineralization in two typical soils in Northwest Guangxi of China under the existence of calcium carbonate, a 100day incubation experiment with the topsoil (0-15 cm) of terra fusca in Karst region and of zonal red soil (as a control) was conducted to study the characteristics of soil OC mineralization under the conditions of three soil moisture gradients (30%, 65%, and 100% waterholding capacity; W1, W2, and W3) and a fixed added calcium carbonate quantity (50 g Ca¹⁴CO₃·kg^-1 dry soil) at 25 ℃. After 100day incubation, the contribution rate of the ¹⁴CCO₂ from added calcium carbonate to the apparent accumulative mineralization amount under W1, W2, and W3 was 9.64%, 6.01%, and 7.63% for the terra fusca, and 34.05%, 27.73%, and 24.18% for the red soil, respectively. The soil OC mineralization rate and accumulative mineralization amount were in the order of W2 > W1 > W3 (P<0.05) for the terra fusca, and of W2, W3 > W1 (P<0.05) for the red soil, respectively. Soil moisture, soil type, and their interaction had significant effects on the soil OC mineralization rate and accumulative mineralization amount (P<0.05). Therefore, when studying the OC mineralization in carbonate-rich soils, especially for the calcareous soils developed in Karst geological background, it would be necessary to consider the effects of soil moisture content and inorganic carbonate decomposition on the soil OC mineralization, and to incorporate these effects into C cycle model to accurately assess the effects of soil inorganic carbon on the soil OC pool.

Key words: rocky mountain area of Beijing., isotope, Quercus variabilis, Platycladus orientalis, water cycle