Soil Microbial Population Characteristics Of Alpine Grassland In The Eastern Qilian Mountains And 16SrDNA Identification Of The Dominant Bacteria As Well As The Action In Grassland

The soil microorganisms, a main part of the grassland ecosystem of grassland, play dorminant roles in the process of organic substance decomposition and conversion, as a result of which influence energy flow and substance conversion.They are also sensitive indicatives of any variation in environmental conditions, microbial community configuration and quantity dynamics can be used to evaluate soil environment and health condition of grassland. Both constitution and quantity of each member of microogansisms in grassland soil as well as microbial diversity are of indispensable significance.In this paper, traditional microbiological methods such as tab isolation and cultivation, physiochemical properties analysis were applied, combined 16SrDNA molecular technique. Seven sites of alpine grassland under different vegetation types in the eastern Qilian mountains in Gansu province were selected for systematic studies on seasonal quantitative dynamics, distributional characteristics of soil microbes community, dominant and special bacteria were also selected for 16SrDNA identification and elementary study on their action of alpine grassland soil substance cycling.The results of the researches showed as follows:1. Seasonal dynamics of soil microbesThe seasonal dynamics of soil microbes of every member of microbial community were not consistent. 1) bacteria the amount of bacteria in Sep.and Nov. were larger than other two months May. and Jul., and there were significant differences between them. The amount of bacteria in May were the smallest. And the variational trend of three shrub sites continually increased with the peak in Nov. and the lowest in May. In grassland sites, the trend of bacteria increased first, and then decreased,.Which had a singal peak. The amount of bacteria in Sep. is the largest. 2) fungi Salix cupularis fruticosa shrub decreased sustainablly with the peak in May and the lowest value in Nov.. Kobresia grassland increased first with peak in July, and then decreased with the the smallest value in May. Grassland sites decreased first and increased later with the peak in Nov. 3) actinomynetes there were two different trends for actinomynetes seasonal dynamics. All shrub sites decreased first and then increased later. And the amount of actinomynetes in May. And Nov. were larger than other tow months. The four grassland sites increased first and decreased later, and then increased slightly with the peak in July. 4) total number of microbes The three shrub sites continally increased with the largest number in Nov. and the lowest in May.. Grassland sites increased first and then decreased with the peak in July (except Swamp grassland). The amount of total microbial number in Swamp grassland was the highest in Sep.2. Vertical distribution of soil microbesThe amount of microorganisms in 0~10cm soil layer was significantly much larger than that of 10~20cm soil layer, microbial quantities decreased as the soil layer becoming deeper.There were much more microorganisms in grassland sites than in shrub sites which showed significant discrepency. Each member of microorganisms under various sites was different: 1) bacteria The amount of soil bacteria in the upper layer was 1.88~3.91 times than that in the low layer, and in the same layer, the amount of soil bacteria in grassland sites was 3.90~16.44 times than that in shrub sites. 2) fungi The amount of soil fungi in the upper layer was 1.17~3.89 times than that in the low layer, and in the same layer, the amount of soil fungi in grassland sites was 2.12~14.60 times than that in crub sites. 3) actinomycetes The amount of soil actinomycetes in the upper layer was 1.16~5.48 times than that in the low layer, and in the same layer, the amount of soil actinomycetes in grassland sites was 19.47~258.36 times than that in shrub sites. 4) total number of microbes The amount of soil total number of microbes in the upper layer was 1.68~3.84 times than that in the low layer, and in the same layer, the amount of soil total number of microbes in grassland sites was 5.82~28.61 times than that in shrub sites.3. Proportion of different soil microbesBacteria and actinomycetes were significantly dominant in alpine grassland soil. Bacteria took the largest proportion in the microbes with the proportion in crub sites and grassland sites 70.12%～97.76% and 32.26%～91.41%, respectively. The proportion of actinomycetes were the second to bacteria with the proportion of 1.98%～29.42% and 8.52%～67.67%. The proportion of fungi were the smallest with the range of 0.05%～1.03% and 0.03%～0.24%. In all sites, the maxmum and minimum of the proportion of different microbial communities occured in different periods. In the three shrub sites, the proportion of bacteria reached peak in Sep. (90.24%～97.76%), and the smallest value occured in May (70.12%～90.42%). The proportion of actinomycetes reached peak in May (9.05%～29.42%). The proportion of fungi reached peak in May. (0.46%～1.03%). In the four grassland sites, the proportion of bacteria, fungi and actinomycetes reached peak in July(32.26%～49.30%), July(50.68%～67.67%)and May(0.14%～0.24%).In July, the proportion of fungi was the smallest(0.03%～0.13%). However, the smallest proportion of actinomycetes and fungi under shrub sites and that of bacteria and actinomycetes occured in different periods.4. 16 SrDNA identification of soil dominant and special bacteria Dominant and special bacteria from alpine grassland were selected according to their morphological and cultural characteristics of the bacteria. And the genomic DNA of these bacteria are extracted for 16 SrDNA identification, which was aimed to establish phylogenetic status. 15 bacteria strains had been identified, the results showed these strains belonged to 8 different genus. HX1 belonged to Lysobacter sp.;HX2,NX4 and WX4 belonged to Arthrobacter sp.;HX5 belonged to Pseudoxanthomonas sp.;HX7,HX32 and WX7 belonged to Pseudomonas sp.;NX2 belonged to Acinetobacter sp.;NX12 and HX31 belonged to Chryseobacterium sp.;NX11,WX3 and HX22 belonged to Flavobacterium sp.;WX15 Brevundimonas sp..5. Action of dominant bacteria in the cycling of grassland substances Eight dominant and special bacteria isolated from the soil of alpine grassland were selected for estimating their motional property, adaptability to the temperature and using ability of various carbon resources and nitrogen resources as well as decomposition of large molecular substances. The results obtained were as follows: bacteria NX2,NX4,NX10 and WX15 had strong motional ability; HX1 and NX2 could grow well at 50C or so , other six bacteria could tolerate low temperature about 00C, which showed good adaptability to alpine climate; There were discrepancy in the using ability and degree of inorganic nitrogen or organic nitrogen, such as nitrate and protein, as well as various carbon resources, which told us those bacteria not only had certain selectivity and played different roles in the decomposition and utilization of animal and plant debris and leavings in the grassland soil, but also collaborated with each other in the process of the subtances cycling and decomposition.