Study On Fractions Of Soil Organic Carbon And Its Sources During Grazing Degradation Of Stipa Grandis Steppe

The research for change of carbon cycle pattern has become a highlight gradually.Grassland ecosystem,as the one of the main ecosystem of land,covered about 1/4 of the land surface.In the past decades,long-term human activities have had a profound impact on grassland ecosystems,esp-ecially on soil organic carbon pools.So carrying on the research on the soil organic carbon fractions and their sources during grazing degradation of Stipa grandis Steppe would help us to understand and master the regulating mechanism of carbon storage in the soil organic carbon pool of Stipa grandis Steppe,which can provide theoretical basis for scientific conservation and rational grazing.This study took free choice grazing steppe of Stipa gra-ndis in Xilingol of Inner Mongolia as research area.The Stipa grandis communities at different degradation stages were selected to investigate quantitative characteristics of C3 and C4 plants,analyze the composition of labile and reluctant soil organic carbon in soil and the stability of soil organic carbon,and illuminate the effect of the change of C3 and C4 plant under different degradation stages of Stipa grandis steppe on the soil organic carbon pool by using stable isotope technique.The main results were as follows:1.The soil organic carbon(SOC),labile organic carbon(LC),reluctant organic carbon(RC)and soil organic carbon density decreased with the increase of soil depth in Stipa grandis Steppe.2.The soil RC,LC content and organic carbon density were the highest in the stage of Stipa grandis + Cleistogen-es squarrosa,while those in the stage dominated by Stipa grandisand or Cleistogenes squarrosa was relatively lower.3.The soil organic carbon mainly derived from the C3 plant in Stipa grandis Steppe,but during the process of grazing the contribution of C4 plant was enhanced in the soil layer of 0-10cm with the decline of Stipa grandis and the growth of Cleistogenes squarrosa.