Effects Of Different Grazing Intensities On Soil Organic Carbon Somponents And Their Stability In Typical Steppe

Grassland ecosystem is one of the most important carbon pools in terrestrial ecosystems,and soil organic carbon component plays an important role in the carbon cycle and regional climate regulation in grassland worldwide.Grazing is the main utilization and management mode in grasslands.At present,the research on soil organic carbon composition and stability mainly focused on soil of farmland and forest.In grassland ecosystem,the influence of grazing intensity is more considered,and yet the research on different livestock types and their mixed grazing mode is rarely studied.Based on the long-term grazing experiments platform set up in Maudeng Pasture in Inner Mongolia Typical steppe,four grazing modes including single grazing of cattle,single grazing of sheep,mixed grazing of cattle and sheep and no grazing were set up in this paper.To determine the effects of four grazing modes of the composition of soil organic carbon and its stability in 2020 and 2021,we analyzed the-aboveground biomass,underground biomass,soil total carbon,soil organic carbon,easy oxidation of organic carbon,particulate organic carbon,mineral combination of organic carbon,microbial biomass carbon and soluble organic carbon.The main results and conclusions are as follows:1.The aboveground biomass of the community significantly reduced under all grazing modes,and that of the mixed-grazing of cattle and sheep was the lowest(72.9g/m~2)in 2020 and reduced by 54.27%.In 2021,the aboveground biomass of cattle grazing was the lowest(110.42g/m~2)and reduced by 44.16%.In 2020,compared with the no grazing(269.17g/m~2),the underground biomass of the community significantly reduced under three grazing modes(196.13g/m~2 for single grazing of cattle,151.82g/m~2 for single grazing of sheep,and 155.75 g/m~2 for mixed grazing of cattle and sheep),with a decrease of 27.13%to 43.6%.In 2021,compared with the no grazing(255.72g/m~2),the underground biomass of the mixed of grazing cattle and sheep(157.84g/m~2)significantly decreased by 37.54%.The fluctuation of annual precipitation was the main reason for the inconsistent performance of aboveground biomass and underground biomass between 2020 and 2021.2.In two years,single grazing of cattle significantly reduced soil organic carbon content(average annual content was 10.9g/kg),while single grazing of cattle and mixed grazing of cattle and sheep significantly reduced soil organic carbon content(average annual content was 59.59mg/kg and 70.75mg/kg);The average decrease of soil organic carbon of cattle grazing was 23.92%,The average annual decrease of easily oxidized organic carbon was 23.74%and 20.86%in single grazing of cattle and mixed grazing.Total organic carbon and easily oxidized organic carbon decreased with the deepening of soil depth,and there were significant differences among different soil layers.3.In 2020,single grazing of sheep and mixed grazing of cattle and sheep significantly reduced particulate organic carbon content(5.21g/kg and 4.72 g/kg),by33.21%and 39.49%,respectively.In 2021,there was no significant difference in particulate organic carbon among grazing modes.In the two years,the average content of mineral bound organic carbon decreased significantly(3.45g/kg),with an annual average decrease of 46.6%.In 2020,single grazing of sheep and mixed grazing of cattle and sheep significantly increased the content of mineral bound organic carbon(7.89g/kg and 7.68 g/kg)by 17.11%and 14.84%.The content of particulate organic carbon and mineral bound organic carbon showed significant difference in 0-30cm soil layer under single grazing of cattle,but no significant difference in 30-50cm soil layer under single grazing of sheep and mixed grazing of cattle.4.The microbial biomass carbon(691.98mg/kg,768.72mg/kg,761.55mg/kg)and soluble organic carbon(57.79mg/kg,54.91mg/kg,55.85mg/kg)significantly decreased by 16.99%,and 32.41%,respectively.There no difference was found between the biomass carbon and soluble organic carbon.There were significant differences in microbial biomass carbon and soluble organic carbon between 0-30cm and 30-50cm under single grazing,but no significant differences among different soil layers between single grazing and mixed grazing.5.In 2020,the rank of soil organic carbon stability was no grazing plot=single grazing of sheep>mixed grazing of cattle and sheep>single grazing of cattle,and the index of soil organic carbon stability in single grazing of cattle decreased by 58.72%compared with the no grazing.In 2021,the rank of soil organic carbon stability was cattle-sheep mixed grazing>no grazing plot=single grazing of sheep>single grazing of cattle.Compared with the no grazing,soil organic carbon stability index increased by 11.19%in cattle-sheep mixed grazing,but decreased by 30.37%in single grazing of cattle.Soil organic carbon stability is affected by soil total carbon and mineral bound organic carbon.