| Understanding the mechanism of soil organic carbon variation is important for fertilizing soil and enhancing cropland soil carbon fixation.The objective of this study was to reveal the different tillage system effects of carbon sequestration in paddy soils, according to the dynamic change characteristics of active soil organic carbon and soil enzyme activities. The main results are summarized as follows:1.The amout of aggregates 0.002-0.02mm was the largest in all trestments, followed by those of 0.02-0.25mm in diameter, with those<0.002mm being the smallest. Lack of soil distrubance enriched in the surface layer(0-5cm) under the DNS,DNT and SNT practices, which may benefit the formation and accumulation of macro-aggregates.2.During rice growth, soil cellulase activities for the size of sorting was DNS>SNT>DNT>PT in 0-5cm soil layer; was DNS>PT>SNT>DNT in 5-15cm soil layer; was DNS>SNT>DNT>PT in 15-30cm soil layer. Compared to PT, no-tillage treatments reduced the size of soil catalase activities, and had no effects on the size of soil sucrase activities. Linear correlation analysis showed that positive linear correlations existed between soil organic carbon and soil cellulase activities, soil sucrase activities, and negative linear correlations existed between soil humic carbon and soil catalase activities.3.During rice growth, soil total organic carbon displayed the trend in 0-5cm soil layer:DNS>DNT>SNT>PT; soil total organic carbon displayed the trend in 5-15cm soil layer:DNS>PT>DNT>SNT; soil total organic carbon displayed the trend in 15-30cm soil layer:DNS>PT>SNT>DNT. Soil humic carbon changes in this study are in accordance with soil total organic carbon, but compared to PT, no-tillage treatment had no effects on the content of soil humic acid and fulvic acid. Compared to PT, DNS treatments was conducive to improving and accumulating the content soil organic carbon.4.Compared to PT, no-tillage treatments reduced the contents of SMBC in 0-5cm soil layer, and increased in 5-15cm and 15-30cm soil layer. Compared to PT, no-tillage treatments significantly increased the contents of WSOC and EOC only in 0-5cm soil layer. Compared to PT, no-tillage treatments increased the contents of the fractions of soil organic oxidized with 333mmol L-1KMnO4, but there was no significantly differents Meanwhile, there was no close correlations existed betwwen soil organic carbon and fractionâ…¢, but there were significantly positive and negative correlativity between soil organic carbon and fractionâ… , fractionâ…¡respectively. After two years rice growing, soil POC displayed the trend in 0-5cm soil layer:DNS>DNT>PT>SNT; soil POC displayed the trend in 5-15cm soil layer:DNT>PT>SNT>DNS; soil POC displayed the trend in 15-30cm soil layer:DNT>PT>DNS>SNT.5.During rice growth, active carbon index changes in this study are in accordance with or early than soil total organic carbon, and its activity increased in the crucial period of crop growth, therefore, active carbon index is more sensitive than total organic carbon and beneficial to crop growth. There were significantly positive correlativity between soil organic carbon and humic carbon, water-soluble organic carbon, soil organic oxidized with 333mmol L-1KMnO4 and its fractionâ… . Soil organic carbon and active carbon index declined with soil depth, and significantly affected by soil depth.6.Carbon pools management index displayed the trend in 0-5cm soil layer: DNS>DNT>PT>SNT; and displayed the trend in 5-15cm soil layer:DNT>PT>DNS>SNT; and displayed the trend in 15-30cm soil layer:SNT>PT>DNS>DNT. The available ratio of soil carbon was EOC/TOC>SMBC/TOC>WSOC/TOC under paddy field. Compared to PT, no-tillage treatments reduced the size of EOC/TOC and SMBC/TOC, increased the size of WSOC/TOC and POC/TOC. Carbon pools management index in DNT treatment were higher than other treatments in 5-15cm and 15-30cm soil layer.
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