Ecosystem conversion affects the dynamic change and cycle of soil organic carbon and environmental quality.The study examined
the total contents of soil organic carbon and the content of soil
active organic carbon and
stable organic carbon in farmland,grassland,scrub and forest ecosystems.The results showed that in all the ecosystems,the total contents of soil organic carbon in 0~10 cm soil were significantly higher than those in deeper soil layer(40~70 cm).In topsoil,the contents of soil organic carbon in grassland,scrub and forest ecosystems separately increased by 82.07%,121.67% and 183.16% compared with the total content of soil organic carbon in farmland ecosystem,and in deeper soil layers the total contents of soil organic carbon appeared to vary similarly;The absolute contents of soil active organic carbon separately increased by 2.24 g/kg,4.13 g/kg and 5.43 g/kg and the absolute contents of stable organic carbon separately increased by 4.76 g/kg,6.23 g/kg and 10.18 g/kg.These indicated that the conversion of farmland system into forest and grassland ecosystems was favorable for the accumulation of soil organic carbon and much more favorable for carbon fixation and ecological environment improvement because it increased the capacity of soil functioning as a carbon sink.