Abstract: Quantitative descriptions of soil organic matter (SOM) dynamics, i.e., their distribution, turnover and movement, are essential for the running of the simulation of terrestrial ecosystem organic matter models. In this study, based on utilizing SOM diffusion translation decomposition model,two soil profiles were selected in different vegetation zones at Dinghushan Mountain for quantitative studies on SOMdynamics and their controlling factors. SOM were divided into three kinds of compartments: rapid compartment with turnover rate of 0.1～1·yr^-1, slow compartment with turnover rate of 0.002～0.02·yr^-1, and stable compartment with turnover rate of 0.0001～0.001·yr^-1. The numerical results suggested that SOM distribution in soil profile in subtropical mountainous areas of south China obeyed the law of diffusion motion, translation motion and decomposition. The turnover rate of SOM rapid compartment was 0.483·yr^-1 in the forest vegetation zone, and was 0.694·yr^-1 in the shrub vegetation zone. The turnover rates of SOM slow compartment in the two kinds of vegetation zones were both 0.02·yr^-1, and the turnover rates of SOM stable compartment in the two kinds of vegetation zones were both 0.001·yr^-1. SOM diffusion rate and translation rate for the forest vegetation zone was 4 cm²·yr^-1 and 0.2 mm·yr^-1, respectively, and the two rates of the shrub vegetation zone were 1 cm²·yr^-1 and 0.5 mm·yr^-1, respectively. The obvious discrepancy between numerical values and measuring values for SOM content occurred in the 0～10 cm sections of the profiles, which might be due to the fact that the upper sections were at the interface between lithosphere and atmosphere, and were influenced directly by changes of climatic and environmental factors. The two kinds of values for SOM content were identical below the upper section of the profiles, and it indicated stable pedogenesis environments. Diffusion motion had obvious influences on SOM vertical distribution, and translation motion had clear impacts on SOM distribution only in the upper 0～10 cm section. Comparison analysis suggested that SOM dynamics were controlled mainly by soil profile qualities such as SOM content, clay content, soil fabric, void types and their developments, soil fauna and microorganism activities, etc. With the increasing of primary production of aboveground vegetation, the turnover rate of SOM rapid compartment decreased and SOM content increased, which provided scientific basis for increasing soil carbon sink through anthropogenic effects.

Key words: SOM dynamics, SOM model, Diffusion motion, Translation motion, Terrestrial ecosystem