Abstract: Two soil profiles were excavated at the forest vegetation zone and the shrub-meadow transitional zone of Dinghushan Mt. (23°09'-23°11'N,112°30'-112°33'E), and thin-layer sampling were conducted for studies on soil carbon dynamics of mountainous soils in the subtropical area. Based on ¹⁴C radioactivity of soil organic matters (SOM), SOM turnover rate (m) is calculated with a numerical model for the upper sections with SOM Δ¹⁴C value greater than zero, due to incorporation of ¹⁴C produced by atmospheric nuclear weapon testing (Bomb ¹⁴C) in the 1960s. As for the lower section with SOM Δ¹⁴C value less than zero, the effect of Bomb ¹⁴C may be neglected due to the slow turnover rate of SOM, and value m is calculated by one specific equation. Value m decreases downward, and is greater than 0.01a^-1 at the upper 12cm section of the soil profiles, then, value m reduces abruptly downward, and is about one magnitude less than that of the above specimen. From 12cm on, value m reduces consistently with depth, till the minimum at the deepest of the profiles. This suggests that soil organic matters are composed of various compartments with different turnover times (T). Rapid compartments (T < 10a) are predominated at the upper 12cm section, slow compartments (100a<T < 1000a) turn to be the main part of SOM downwards, and stable compartments (T > 1000a) are predominated at the lower sections of the profiles. CO₂ production resulted from SOM turnover is calculated based on value m, organic carbon content, soil bulk density and soil section thickness. The results suggest that the CO₂ production from the upper 12cm section is about 98 percent of the total CO₂ production of one profile. Therefore, the upper 12cm section is the main contributor for CO₂ emission due to SOM decomposition in one soil profile. CO₂ flux of the upper 12cm section of SL profile is 0.1233gC/cm²·a, which is about one magnitude higher than that of the upper 12cm section of GC profile. This is ascribed to that value m and organic carbon content of the upper 12cm section of SL profile are greater than those of the upper 12cm section of GC profile, respectively. For example, value m of the upper 12cm section of SL profile are greater than 0.1a^-1, and those of the upper 12cm section of GC profile are from 0.01a^-1 to 0.08a^-1. Value m of the uppermost specimen is 0.402a^-1 for SL profile, and is 0.078a^-1 for GC profile; the former is about one magnitude higher than the latter. The aboveground vegetation types contrast obviously between SL profile and GC profile, which results in different primary production of aboveground vegetation for the two spots. Soil organic carbon content and value m of SOM are controlled directly by primary production of aboveground vegetation. Therefore, aboveground vegetation is the key factor controlling SOM turnover and the corresponding CO₂ production of soil profiles within one climatic zone, which give scientific supports for increasing soil carbon sink through afforestation. The upper soil section has high SOM content and great value m, and is apt to be eroded away, thus, the upper section of one soil profile is prone to be CO₂ source. Plant debris is the main source for SOM of the upper soil section. Therefore, to reduce plant debris production and to increase the biomass of deep roots, in order to transfer more organic matters into the deep, may be one effective measure for reducing and slowing down the emission of CO₂ due to SOM turnover. For this purpose, vegetation with high underground biomass should be planted firstly under all possible conditions, which needs comprehensive cooperation between soil scientists and botanists.