Effect Of Stocking Rate On Community Characteristics And Ecosystem Carbon Budget Of Stipa Breviflora Desert Steppe

The grassland ecosystem functioning has been seriously weakened in globe due to many environment factors, mainly including climate change, human activities and its chemical circulation. Therefore, ecosystem function restoration and original mechanism maintain urgently depended on improving grazing management, which is an important scientific debate in the development of grassland animal husbandry.The experiment was selected in desert steppewith different stocking rates, for a long-term comparison in order to understand the change of community characteristics, soil status, carbon sequestration ability, and carbon budget of grassland ecosystem among different sheep stocking rates. The study will reveal the carbon sequestration potential of grassland ecosystem in different stocking rates, obtain the optimal stocking rate from carbon balance point of view, and thus it will provide a theoretical basis for the maintenance of grassland carbon sequestration and sustainable utilization of grassland.This study site is in desert steppe with dominant species of Stipa breviflora and located at Siziwang Banner, Wulanchabu of Inner Mongolia. The completely randomized block experiment was conducted on natural grassland with same status of natural conditions. Four different stocking rate treatments were established: control(CK), light grazing(LG), moderate grazing(MG) and heavy grazing(HG), respectively. The stocking rates were 0, 0.91, 1.82 and 2.71 sheep ha-1 half year, respectively with three replications. Grazing was assigned in warm season each year, 9 years date were collected. Vegetation, soil and ecosystem carbon budgets were measured at different stocking rates. The main conclusions were summarized as follows:The grassland standing crop, coverage, height, density of grassland community and dominant species significantly decreased with the increase of stocking rate(P<0.05), and the interaction of stocking rate and year was of significant effects(P<0.05). From the functional group level, shrubs and semi-shrubs were of significant change with stocking rate increase(P<0.05). The proportion of perennial bunchgrass increased with the increase of stocking rate, while the percentages of shrub, semi-shrub and perennial forbs decreased. Community biodiversity was mainly affected by hydrothermal factors in Stipa breviflora desert steppe of Inner Mongolia, water is the main limited factor in the grassland type. There was a direct relationship between the different stocking rate and rainfall from May to July. When rainfall was low, the grassland ecosystem was of weak effect to the stocking rate, but rainfall reached a certain level, stocking rate affacted significantly. In this type of grassland, rainfall played a critical role, stocking rate was second.The distribution trend of belowground biomass mainly was in the surface layer of 0-30 cm in Stipa breviflora desert steppe of Inner Mongolia, about 80% of the total of belowground biomass, 50% belowground biomass concentrated in 0-10 cm soil layer. The soil layers of biomass showed the !T" type distribution with the increase of soil depth. The influence of different stocking rates on belowground biomass mainly was occurred in 0-30 soil layer.There was no change on soil characteristics in essence during 9 consecutive years with different stocking rates. However with the increase of stocking rate, soil physical and chemical properties caused the slight different change, but the change of soil characteristics showed a certain time lag, the soil characteristics is not sensitive to grazing disturbance in the short term.The amount of fixed carbon with underground significantly decreased with the increase of stocking rate in Stipa breviflora desert steppe ecosystem, fixed carbon content decreased by 74% in heavy stocking rate. The amount of fixed carbon with root decreased with the increase of stocking rate, more than 70% of the fixed carbon of root mainly concentrated in the surface layer of 30 cm soil layer. Soil organic carbon content decreased with the increase of soil depth, stocking rate and soil layer depth was of a significant effect on soil organic carbon content and reached the maximum in light grazing. The trend of soil microbial biomass carbon showed decease with the increase of soil layer. The different stocking rates were of has the significant effects on soil microbial biomass carbon occurring only in the surface 0-10 cm soil. The organic carbon content of soil aggregate decreased with the increase of stocking rate. In the 0-30 cm soil layer, soil organic carbon content of 1 mm size partical in control and light grazing were higher than other size. Stocking rate was of no significantly effects on total of carbon content, light group of organic carbon in desert grassland. The total of soil carbon was not obviously response to stocking rate.There was 96% of carbon in the soil.There was no significantly response to stocking rate in Inner Mongolia desert grassland on carbon storage of ecosystem, the ecosystem carbon sequestration potential ranged from 23.77 103 kg ha-1 to 27.51 103 kg ha-1, the average carbon sequestration capacity was 25.86 103 kg ha-1.To summarize vegetation, soil and ecosystem carbon budget in Inner Mongolia desert grassland, it was concluded that suitable stocking rate was 0.91 sheep/hm2/half year in Inner Mongolia desert grassland. In other word, the suitable stocking rate was the moderate stocking rate in the experiment, the ecosystem will be degraded in different extent when the stocking rate exceed the suitable stocking rate in Stipa breviflora desert steppe of Inner Mongolia.