Abstract: To clarify the distribution and change characters of different organic carbon forms in ancient paddy soils, the difference and profile distribution characteristics of soil organic carbon (SOC), easilyoxidized organic carbon (EOOC), watersoluble organic carbon (WSOC), and active organic carbon (AOC) contents were studied between the buried ancient paddy soil and the present cultivation paddy soils in Shanlonggang Village, Hunan Province. The results showed that the contents of SOC, EOOC, WSOC, and AOC in the cultivation layer were lower in the buried ancient paddy soil than in the present cultivation paddy soil, and their average contents accounted for 51.86%, 28.24%, 40.12% and 34.17% of the present cultivation paddy, respectively, while no obvious difference was observed among the plow pan, the waterloggogenic horizon and the parent material horizon. The contents of WSOC, EOOC, and AOC accounted for 0.45%, 37.34%, 16.39% of the total carbon in the cultivation layer in the buried ancient paddy soil, being 0.38%, 10.93%, and 8.48% lower than that in the present paddy soil, respectively. The content of WSOC decreased with the increase of soil depth, while the contents of EOOC and AOC showed a trend of increasedecreaseincrease. The SOC content in the cultivated horizon was 28%-52% lower in the buried ancient paddy soil than in the present paddy soil, but that in the plow pan, waterloggogenic horizon and parent material horizon was higher in the ancient paddy soil than in the present paddy soil, indicating the organic carbon accumulated 3000 years ago still stored in the ancient paddy soil. These results suggest that the contribution of paddy wetland to soil organic carbon pool is relatively stable, playing an important role in global carbon cycling and the ecological and environmental protection.

Key words: open top chamber, elevated ozone concentration, organic acid., rhizospheric soil, enzyme activity