Study On The Characteristics Of Soil Organic Matter Of Alpine Meadow Under Different Degradation Degrees In Eastern Qilian Mountains And Its Effect On Productivity

Based on the investigation and analyses on the plant communities of alpine meadow in Jinqiang River valley of Tianzhu Country, Gansu Province, three representative sampling plots were selected according to the degradation degree and utilizing pattern, and they were marked as non-degraded meadow (ND); moderately degraded meadow (MD) and heavily degraded meadow (HD). The differences and characteristics of soil organic matter (SOM) were studied. Meanwhile, its relationship between soil nutrient contents (nitrogen and phosphate) and primary productivity and the species diversity were discussed. The conclusions were summarized as follows:1. Characteristics of plant communities of degraded alpine meadowBecause of long-term 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 (Kobresia spp., Polygonum viviparum) of plant communities 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 MD and ND, the coverage of HD 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 meadowThe soil moisture and the soil bulk density showed evident vertical changes with the soil depth. The soil moisture decreased gradually (MD increased in upper layer and then decreased in lower layers), on the contrary, the bulk density of soil increased. With the degradation degree, the soil moisture decreased gradually but the bulk density of soil increased.3. Change of soil organic matter content and its composition features of degraded alpine meadowThe content of SOM and its composition features showed different change patterns among soil layers, seasons and degraded degrees. The content of SOM decreased with the increase of soil depth .The content of SOM showed significant differences among the soil depth and soil layers (p<0.05 or p<0.01). The seasonal variation was also obvious among different months. The content of SOM increased in the period of May to September and then decreased in November. There were significant differences among different degraded degrees grassland. With the soil depth and degraded degrees, the content of humus and humic acid decreased; the ratio of HA/FA were ranged from 0.95 to 1.35 and at the same soil layer ND>MD>HD; the ratio of E4/E6 and oxygen-containing functional groups in humic acid decreased.4. Relationship between SOM and soil nitrogen and phosphate contentsResults showed that SOM was significant positive correlation with total nitrogen, total phosphorus and available phosphorus (p<0.01), and the correlation with total phosphorus was the strongest. SOM had positive correlation with available nitrogen (0.01