Study On Relationship Between Soil Microorganisms And Degradation Of Grassland In Steppe Under Different Carrying Capacities In Longdong Of Gansu

Based on three different treatments: NO1(WS1) carrying capacity is 8 sheep/hm2; NO2(WS2) carrying capacity is24 sheep/hm2; NO3(WS4) carrying capacity is 16 sheep/hm2; and one control: NO4(WS3,CK) enclosed grassland exempt from grazing (EGEG), quantitative dynamic change against seasons, physiological flora, dominant genera species under different carrying capacities in steppe of Huan Country of Gansu Provirce were studied in this paper. The results showed as follows:(1).Physicochemical properties of grassland soil General characteristics such as low content of organic substance, total nitrogen and phosphorus; medium of alkaline hydrolytic nitrogen, extreme low of available phosphorus.The EGEG and grazing properly are significantly effective in humidity improvement and fertility rehabilitation of grassland soil.(2).Dynamic change against seasons of soil microorganism Flourishing of soil microorganisms(fungi and bacteria) were in June and in July contrasted with their small quantity in October except for actinomyces. The total number of microorganism in 2003(Ñ…104CFU/g dry soil)showed the largest quantity (1918.2)in WS1 and the smallest (1428.93)in WS4. Quantitative pattern of various microorganisms among different samples were compared. 1)Bacteria were dominant regardless of the months and samples. Its annual proportion against total bacteria in respective samples reached 84.73%,75.54%in WS1,WS2 samples respectively, but there was a relative smaller fluctuation in WS3. 2)Fungi's annual proportion against total fungi in respective samples reached 0.21%,0.13% in WS4,WS3 samples respectively. 3)Actinomyces showed the largest quantity (360.95)in WS2 and smallest (228.35) in WS3, its proportion against total actinomyces in respective samples reached 24.26%,13.19%in WS2,WS3 samples respectively. These data suggested that both EGEG and proper grazing could improve the number of soil microorganisms in order to renew the degenerate grassland. Among three kinds of microorganisms, bacteria were the dominant and with the augment of carrying capacities, the number of bacteria decreased while fungi and actinomyces increased. (3). Physiological flora of soil microorganisms Both ammonifiers and azotobacter were abundant in four samples. Nitrogen cycle related to microorganism group such as ammonifiers, cellulolytic microorganisms and azotobacter all gradually declined with increasing carrying capacities while Bacillus reversed. It showed that ammonification were stronger in four samples and anaerobic cellulolytic microorganisms were very scarce,which suggested that the cellulose lysis from local plants depended on aerobic cellulolytic microorganisms. Meanwhile, the number of nitrogen cycle related to microorganisms was larger inWS1 than in WS3. (4).Genera of microorganisms and dominant ones HJ4 and Bacillus appeared dominant in all tested samples. There were a few differences between EGEG and other grazing samples also. For example, HJ13,HJ18 were dominant in grazing samples while minor in EGEG. Difference also appeared between different carrying capacities samples. Apart from the same general pattern as bacteria, Fusarium sp appeared as the dominant fungeous genus in all four samples. Among different carrying capacities samples, difference appeared as well.