Abstract: This paper studied the pool sizes and turnover rates of organic carbon in paddy soil,upland fluvo-aquic soil and red soil in Yujiang County.According to the turnover time of soil organic carbon,the carbon pools could be clssified into active,slow­active,and inert pools,all of which complied with first order dynamic model.Based on the decomposition curves of soil organic carbon and employing this model,the sizes and decomposition rates of active and slow­active carbon pools were simulated,and the results showed that the size of active pool in different soil profiles accounted for 0.6%～3.7% of total soil organic carbon,with a mean residence time of 4～45 days,while the size and mean residence time of slow­active pool were 37.7%～81.2% and 5～24 years,respectively. As for inert pool,its size measured by using acid hydrolysis method accounted for 17.1%～48.1%.The carbon pool size of paddy soils with different moisture regime was in  order of periodically waterlogged paddy soil> glayed paddy soil> submerged paddy soil,while that of paddy soils with different parent material was in  order of Quaternary red clay >Tertiary red sandstone.Paddy soils had a larger active carbon pool than upland soils,which was reverse in slow­active carbon pool,suggesting that upland soil had a greater ability to fix carbon than paddy soil.

Key words: Petrophytia moss, Forest vegetation, Disturbance, Water and soil conservation