Properties Of Microorganism Communities Under Different Alpine Grasslands In Eastern Qilian Mountain

Six different representative grassland types in Eastern Qilian Mountain were selected to investigate their soil properties of microorganism communities in May (spring), July (summer) and November (late autumn). They are No 1, Kobresia meadow; No 2 , Dasiphoru fruticosa shrubs meadow; No 3, Polygonum viviparum-Kobresia meadow; No 4, Salix cupularis-dasiphoru fruticosa shrubs meadow; No 5, alpine steppe, and No 6, swamp meadow. All above grasslands grazes only with yaks and Tibetan sheep in winter. The quantity of soil microorganism and its biomass carbon and nitrogen, the different functional groups of soil microorganism, and their relationships and soil characteristic were analyzed, based on principles of soil microbiology and pedology. The main research results are as follows: 1. The seasonal dynamics of soil microorganism quantities There were significant change with seasons in soil microorganism quantities (p<0.05), the total quantity of soil microorganism decreased as season progress. Compare of the three seasons, there were more microorganism in May, and least microorganism in November. In terms of the seasonal change of soil microorganism in quantity, the quantity of Bacteria group in Polygonum viviparum-Kobresia meadow and Swamp meadow reduced acutely (85.70% and 82.51% respectively), while that in Dasiphoru fruticosa shrubs meadow reduced slightly (27.95%) from Spring to late Autumn; The similar trend was also found in Polygonum viviparum-Kobresia meadow (63.09%) and in Dasiphoru fruticosa shrubs meadow (12.57%) for Fungi group; However, the reverse tendency was showed in Actionmyces group compare to Fungi and Bacteria groups, i.e. in Dasiphoru fruticosa shrubs meadow (60.60%) and in Polygonum viviparum-Kobresia meadow (33.67%). The quantity of bacteria group was most compared to other two groups in the alpine grassland system, it accounted for 75.82%-97.31% against total soil microorganism, while Actinomyces group and Fungi group were only 2.68-24.17% and less than 0.1%, respectively. 2. Microorganism quantities at various soil depths Vertically quantitative distribution of various microorganism groups showed that, the deeper the soil, the less the microorganism. (1) exception of Dasiphoru fruticosa shrubs meadow Bacteria group in the all plots reached significant level (p<0.05); (2) Fungi group showed not significant level (p>0.05) only in Kobresia meadow and Dasiphoru fruticosa shrubs meadow. (3) Actinomyces group: It showed significant only in Kobresia meadow, while that in the other was not significant. 3. Microorganism quantities in various grasslands The horizontal distribution of soil microorganism was related to soil characteristic and plant community. In this experiment, the quantity of bacteria group showed significant between different sampling sites, which was most in Polygonum viviparum L.-Kobresia meadow, and least in Grass steppe and Swamp meadow(p>0.05). Among the six sites, Kobresia meadow had more fungi group than the other sites, Grass steppe had the least. The quantity of actinomyces group also showed significant between different sampling sites, which was the most in Grass steppe and Kobresia meadow, and the least in Salix cupularis-dasiphoru fruticosa shrubs meadow (p<0.01). In terms of the total quantity of soil microorganism, it showed an extremely positive relationship between it and total soil nitrogen, total soil phosphorus (p<0.01), and a positive one between it and soil organic carbon, pH, the underground biomass of plant. However, the relationship between it and the ratio to soil organic carbon and microorganism biomass nitrogen was not significant. 4. Soil microorganism functional groups Among the different soil microorganism functional groups in this Alpine grassland system, the order of the quantity of them was that: Aerobe cellulolytie > Oligotrophpic cellulolytic > Dinitrifying bacteria > Oligotrophic Azotobacter > Nitrifiers. 5. The characteristics of soil organic carbon and total nitrogen The content of soil organic carbon was approximately 3.07%-9.39%; total nitrogen was 0.380%-0.797%. The soil organic carbon had an extremely positive relationship with total nitrogen. The content of soil organic carbon and total nitrogen in the top soil layer (0-10cm) comprised most than that at the deeper layer (10-20cm) against the sum of the content of the two layer, respectively. 6. The characteristics of soil microorganism biomass The content of soil microorganism biomass carbon was from 263.9-1562.5 mg/kg , it was most in the top soil layer(0-10cm) in swamp meadow, least in 10-20cm layer in grass steppe; the similar result was found in soil microorganism biomass nitrogen in the top soil layer(0-10cm) in Dasiphoru fruticosa shrubs meadow (53.7 mg/kg ) , and least in 10-20cm layer in Salix cupularis-dasiphoru fruticosa shrubs meadow (16.2 mg/kg), and they differ with plant communities.