Forms Character And Mineralization Processes Of Organic Carbon In Ancient Paddy Soil

Soil carbon pool is one of the largest carbon pools in the terrestrial ecosystem, soil organic carbon storage and discharge has important significance for the global carbon cycle and global climate change. The content difference and the mineralization cumulative amount were studied between the buried ancient paddy soil and the present cultivation paddy soils in Shanlonggang Village, to clarify the distribution characteristics of different organic carbon forms and the mineralization processes in ancient paddy soil. The main results as follows:(1) The content of soil organic carbon (SOC) was reduced with soil depth increase in the buried ancient paddy soil and the present cultivation paddy soils. The content of the soil organic carbon (SOC), the easily-oxidized organic carbon (EOOC), the water-soluble organic carbon (WSOC), the active organic carbon (AOC) was lower in the buried ancient paddy soil than the present cultivation paddy soil in the cultivation layer, and their average content accounted for 51.86%,28.24%,40.12% and 34.17% of the present cultivation paddy.(2) The different organic carbon forms were close among the soil layers in ancient paddy soil, and the content of the WSOC, the EOOC, the AOC, which in the plow pan, the waterloggogenic horizon, was higher than the cultivation layer. The contents were differences between the cultivation layer and the plow pan in the present cultivation paddy soils, and there obvious difference was not observed among the plow pan, the waterloggogenic horizon and the parent material layer.(3) The SOC mineralization cumulative amount was lower in the buried ancient paddy soil than the present cultivation paddy soils, the cumulative amount of the cultivation layer, the plow pan, the waterloggogenic horizon and the parent material layer was accounted for 14.9%,45.5%,62.5%,75.0% of the present cultivation paddy.(4) The SOC mineralization rate was lower in the buried ancient paddy soil than the present cultivation paddy soil, and gone down over time. The highest rate was in the first day in the cultivation layer, the waterloggogenic horizon and the parent material layer. It was less than 0.5 mg C/(g·d) within 3 days in the cultivation layer, the plow pan and the parent material layer, and was less than 0.1 mg C/(g·d) during 28 days in the plow pan and the waterloggogenic horizon. The mineralization rate was more than 1 mg C/(g·d) during 7 days in the present cultivation paddy soils, and gone down to 0.19 mg C/(g·d) within 180 days. It was less than o.5 mg C/(g·d) after 14 days in the plow pan and the waterloggogenic horizon, but the rate of the parent material horizon was more than 0.5 mg C/(g·d) during the 3 days.(5) The accumulation organic carbon before 3000 year still stored in the ancient paddy soil, the organic carbon mineralization rate was obviously lower in the buried ancient paddy soil than the present cultivation paddy soils. There was negative correlation between potential mineralization and soil depth, and was positive correlation between potential mineralization and the SOC, the WSOC, the EOOC,the AOC and pH.