Study On Differences Characteristic Of Soil Organic Carbon Of Different Land-use Type In Dry Valley Of The Upper Reaches Of Minjiang River

Soil organic carbon pool is a major component of the terrestrial carbon pools, and plays an important role in the research of terrestrial carbon cycle. Its minor changes will have a major impact on global climate change, Land-Use and Land-Cover Change (LUCC) which is caused by human activity is the most direct factor in affecting the soil carbon pool. As one of the arid center of China’s Hengduan Mountain, The dry valley of the Upper Reaches of Minjiang River has the characteristics of unique climate and fragile ecological, so it is very sensitive to land use changes. Combining with the background of continuous degradation of ecological in dry valley in recent decades, The local representative of land use types are selected in this study, such as, Young Plantation, abandoned wasteland, farmland, cash crop, brushwood, artificial mixed forest, natural secondary forest, natural forest. The main results are as follows:(1) The differences of SOC concentration and its density among different land use types are significant. The mean of SOC concentration was respectively that natural secondary forest(20.77g·kg-1)> brushwood(17.83g·kg-1)> artificial mixed forest(16.32g·kg-1)> Young Plantation(15.41g·kg-1)> natural forest (15.18g·kg-1)> farmland(10.73g-kg-’)> abandoned wasteland(10.27g·kg-1)>cash crop(9.74g·kg-1); the mean of soil organic carbon density was respectively that brushwood (3.09kg·m-2)> natural secondary forest(2.99kg·m-2)> artificial mixed forest (2.93kg·m-2)> natural forest(2.32kg·m-2)> Young Plantation(2.19kg·m-2)> abandoned wasteland(1.75kg·m-2)> farmland(1.62kg·m-2)> cash crop(1.35kg·m-2). Compared with abandoned wasteland and farmland, forestland could further contribute to the accumulation of SOC, but the concentration of cash crop SOC was lower for strongly interference.(2)The SOC stability among different land use types were various. The concrete expression is that the concentration of heavy fraction organic carbon(HF-OC) and difficulty oxidizable organic carbon and their ratios were various. The mean of HF-OC concentration was respectively that brushwood (14.93g·kg-2)>natural secondary forest (14.75g·kg-2)> artificial mixed forest (12.20g·kg-1)> Young Plantation (9.29g·kg-1)> natural forest (8.77g·kg-1)>farmland (8.69g·kg-1)>abandoned wasteland (8.12g·kg-1)> cash crop (7.05g-kg-’), and their ratios were between0.573and0.842;the mean of difficulty oxidizable organic carbon concentration was respectively that natural secondary forest(15.52g·kg-1)> brushwood(14.48g·kg-1)> artificial mixed forest(12.87g·kg-1)> young Plantation(11.85g·kg-1)> natural forest(10.52g·kg-1)> abandoned wasteland (8.24g·kg-1)>farmland(7.75g·kg-1)>cash crop(7.53g·kg-1), and their ratios were between0.683and0.829. From what has been discussed above, the SOC stability of natural secondary forest, brushwood and artificial mixed forest are higher, and compared with single forest types and farmland, artificial mixed forest and abandoned wasteland are helps to the accumulation of SOC and its components. Moreover, exogenous interference have a major impact on SOC stability.(3) The quality of soil organic carbon pool among different land use types were various. The concrete expression is that the concentration of light fraction organic carbon(LF-OC) and particulate organic carbon(POC) and their ratios were various. The mean of LF-OC concentration was respectively that natural secondary forest(6.28g·kg-1)> young plantation(4.84g·kg-1)>natural forest(4.45g·kg-1)>farmland(2.55g·kg-1)>artificial mixed forest(2.01g·kg-1)> brushwood(1.90g·kg-1)> cash crop(1.44g·kg-1)> abandoned wasteland(1.40g·kg-1), and their ratios were between0.088and0.241; the mean of POC concentration was respectively that natural secondary forest(10.70g·kg-1)> natural forest(9.68g·kg-1)> brushwood(9.46g·kg-1)> artificial mixed forest(8.32g·kg-1)> young plantation(7.82g·kg-1)> farmland(5.42g·kg-1)> abandoned wasteland(4.39g·kg-1)> cash crop(2.85g·kg-1), and their ratios were between0.404and0.502. From what has been discussed above, the qualities of natural forest and natural secondary forest are higher than others, the active components of SOC would decrease if natural forest had been destroyed, plantation forest would help to improve the concentration of LF-OC and POC, while cash crop had the worst soil organic carbon pool.(4)At the vertical profile of soil0-100cm, in general, with soil depth increased, the concentration of SOC, HF-OC, difficulty oxidizable carbon, LF-OC, and POC decreased significantly, however, the extent of reducing are different. The distribution regularity of ratio about the components of carbon are also various, and Shows a layer characteristic, but the layers are different, the differences in layers are not significant within group but significant among groups. The concentration of SOC and its components carbon are higher in0-40cm soil layers, those show that distribution differences of litter, roots and its secretions within layers and human disturbance are the main factors that the concentration difference of SOC and its components carbon in various layers. Therefore, LUCC will lead to changes in the surface soil organic carbon pool.