Effect Of Land Use And Landscape Position On Soil Labile Organic Carbon In The Hilly Red-soil Area Of The Mid-subtropical Climatic Zone

Soil is the largest carbon reservoir in terrestrial ecosystems and can act as both a sink anda source in response to changes in climate, land use, and atmospheric CO₂. Currently, a fewstudies have examined the effects of land use changes on soil labile organic carbon. However,the change of labile organic carbon （LOC） was different in different land use and differentstudy region for the complicate process of land use affecting on LOC. The influencingmechanism of land use change on LOC in typical landform region need further study. Givingthe increase in global land degradation, soil erosion and atmospheric CO₂concentrations, theeffects of land use types and landscape position on LOC in severely eroded soil is importantfor the assessment of soil quality and the accurate determination of the potential of soil carbonsequestration. LOC is more sensitive to changes in land management or environmentconditions than stable carbon, although it is a smaller fraction of soil organic carbon （SOC）. Italso has a disproportionately large effect on nutrient-supplying capacity and the structuralstability of soils. Therefore, soils samples from cultivated land（CL）, pine forest （PF）, barrenhill （BH）, citrus orchard （CO）, Cinnarnornum camphora plantation （CC） located in the redsoil hilly region of southern China were selected to study the effect of land use and landscapeposition on soil labile organic carbon in the hilly red-soil area of the mid-subtropical climaticzone. The characteristics and affecting factors （topography, vegetation and soil properties）have been also analyzed in Pinus elliottii ecosystem of red soil hilly region. It is important forfurther standing of the character of SOC and the assessment of soil quality and the accuratedetermination of the potential of soil carbon sequestration in hilly red-soil area of themid-subtropical climatic zone. It can also provide scientific basis for establishing the responseof Pinus elliottii ecosystem to climate change.（1） Microbal organic carbon （MBC） varied from23.97mg.kg^-1to192.84mg.kg^-1, variedin the order of Cinnarnornum camphora plantation>citrus orchard>barren hill>pine forest>cultivated land; the trend of dissolved organic carbon （DOC） was different from MBC,which varied from34.24mg.kg^-1in Cinnarnornum camphora plantation to286.44mg.kg^-1incultivated land. EOC had similar trend with MBC, with the average value between1.03g.kg^-1to3.20g.kg^-1. The distribution of MBC, DOC and EOC on the slope followed the same rankorder of upper slope>lower slope>mid-slope.（2） Carbon management carbon （CMI） in five land use had similar change trend:Cinnarnornum camphora plantation>citrus orchard>cultivated land>pine forest>barren hill, the slope site difference of CMI in each land except cultivated land was also obvious，with thetrend of upper slope>lower slope>mid-slope, which was similar to easily organized carbon.（3） Results indicated that the mean of soil organic carbon（SOC）,easily organizedcarbon（EOC）, microbal organic carbon（MBC） and dissolved organic carbon（DOC） was6.58g.kg^-1,1.92g.kg^-1,129.44mg.kg^-1and51.13mg.kg^-1, respectively; coefficient of variabilitywas31.16%，40.63%，65.71%and85.06%, respectively, all of the four indexes are moderatevariabilities. SOC, EOC and MBC had similar trend of spatial distribution, that is, thenorthwestern area and gully had the highest value, the soil on the slope had lower value.