Carbon Storage And Its Influencing Factors In Xinjiang Grassland

Comprehensive and accurate measurement of carbon density and understanding the influence mechanism of its spatial distribution in Xinjiang grassland is of great significance to estimation of carbon storage and sustainable use in China's grassland.In this study,we used588 sampling points and analyzed the spatial distribution of biomass carbon density and soil carbon density in Xinjiang grassland.We utilized Partial Least Square Path Modeling to understand the influence of climate conditions,elevation,plant species richness and soil properties on carbon density.The main results were:(1)The average value of carbon content in plants was 410.89 gC/kg in Xinjiang grassland being lower than 45%or 50%of empirical value;The average value of aboveground and belowground biomass was 62.94 gC/m~2 and 632.88 gC/m~2 respectively.Belowground biomass was 13.03 times higher than aboveground biomass;The average value of soil inorganic carbon density and soil organic carbon density to 100cm depth was 15.45 kg/m~2and11.81 kg/m~2 respectively.The average value of total soil carbon density was 27.46 kg/m~2and inorganic carbon accounted for 61%.There were significant difference in biomass carbon density and soil carbon density between grassland forms and the same was true for grassland types.Biomass carbon density and soil organic carbon density of meadow was highest,followed by steppe.Biomass carbon density and soil organic carbon density of desert was smallest.Soil inorganic carbon density was opposite to biomass carbon density and soil organic carbon density in spatial distribution.(2)Our study showed that shrub changed significantly aboveground and belowground carbon density in Xinjiang grassland by comparing the living aboveground biomass,litter,belowground biomass,soil organic carbon content at different depths and soil organic carbon density between grasslands dominated by shrubs or grass among six grassland types.Shrub significantly increased living aboveground biomass and litter and the increasing extent was higher in steppe,meadow steppe and mountainous meadow than in desert,steppe desert and desert steppe.Belowground biomass,soil organic carbon density and soil organic carbon content at the upper layer were higher in pure grassland in desert,steppe desert and desert steppe.In semiarid grassland,there no significant difference in belowground biomass between the two physiognomic types.Soil organic carbon content at the upper layer were higher in wooded grassland in steppe,meadow steppe and mountainous meadow.Wooded grassland had higher soil organic carbon density in temperate steppe meadow and mountainous meadow.The change in soil organic carbon density was positively with mean annual precipitation,and negatively with mean annual temperature.Our results indicated that the effect of shrubs changed from negative to positive along the precipitation and temperature gradient.Climatic conditions mediated the effect of shrubs on C storage by affecting plant productivity and the interaction between shrubs and grass.(3)The most important influencing factor for above ground biomass density was soil pH and there was negative correlation between aboveground biomass density and soil pH in Xinjiang grassland.Climate conditions,elevation,soil properties and plant species richness had significant influence on belowground biomass and the strength of elevation was greatest.Soil bulk density,thickness and pH value had the biggest influence on soil organic carbon density and elevation had the biggest influence on soil inorganic carbon density.(4)Biomass carbon stock in Xinjiang grassland was 0.4423 PgC;Soil inorganic and organic carbon stock was 9.1257 PgC and 7.1144PgC respectively.Total carbon stock in Xinjiang grassland was 16.6824 PgC.