Study On The Soil Organic Carbon Stock Of Alpine Grassland Under Different Degraded Degrees In Eastern Qilian Mountains

Based on the investigation and analyses on the plant communities of alpine grassland in Jinqiang River of Tianzhu Country, Gansu Province, the sampling plot of grassland under different degraded degree (heavily degraded grassland, HDG; moderately degraded grassland, MDG; and light degraded grassland, LDG) was selected and the soil organic carbon (SOC) and nitrogen storages, its variation patterns among seasons and soil layers were assayed and analyzed, meanwhile, the key affecting factors were probed. The conclusions were summarized as follows:1) Features of plant communities of degraded alpine grasslandBecause of long time continuous grazing pressure, the grassland was degraded in different degrees and the species diversity, richness and evenness of plant communities were obviously decreased. The dominant plant species of plant communities (Kobresia spp., Polygonum viviparum) were replaced by forbs and poisonous grasses (Oxytropis spp., Pedicularis spp., Gentiana spp.). The total coverage and aboveground phytomass of grassland decreased along with the degraded degree. Compared with the middle degraded and light degraded grassland, the coverage of heavily degraded grassland decreased by 2.05% and 6.3%, and the aboveground phytomass decreased by 55.33% and 73.38% respectively.2) Soil properties of degraded alpine grasslandAlong with the soil depth of degraded alpine grassland, the soil moisture decreased gradually and the bulk density of soil increased on the contrast. The soil organic carbon and total nitrogen contents obviously decreased and shown an upper-accumulated pattern. The soil moisture decreased and the bulk density of soil increased along with the degraded degrees. The C/N ratio of soil ranged from 1:11 to 1:16.3) SOC stock of alpine grassland under different degraded degreesThe SOC stock of alpine grassland under different degraded degrees showed different variation patterns among soil layers, seasons and degraded degrees. The content of SOC decreased with the increase of soil depth and its average values were ranged from 0.820 to 0.858 kg/m~2 (0-10 cm), 0.706 to 1.254 kg/m~2 (10-20 cm) and 0.660～1.056kg/m~2 (20-30 cm) respectively. The SOC stock showed a decreasing trend along with the soil depth and the...