| The Tetraena mongolica Maxim core area belongs to the semi-arid area of the western Ordos Plateau.Its natural environment is dry and rainless,with strong winds and sand,rough soil and poor nutrients.Its plant species are poorly formed,and they are hard to growth.One third of them is ancient,endangered,rare and endemic plant species.Plant rhizosphere-promoting functional bacteria can promote plant growth and its absorption and utilization of mineral nutrients,and can inhibit harmful organisms and improve plant resistance.Therefore,taking the rare and endangered plant communities such as Tetraena mongolica,Sarcozygium xanthoxylon,Reaumuria trigyna,and Salsola passerina as research objects,this paper studys excellent growth-promoting strains by Screening and Identifying Functional strains which can promote the rhizosphere soil of plants,and conducts homology alignments to its 16 Sr DNA gene sequence,and explores the growth promoting effects by germination test and pot experiment.It provides some theoretical basis for protecting rare and endangered plants and improving the poor environment.The main results are as follows:1.The physical and chemical properties of the rhizosphere soil of four plants in the study area are pH 8.45-8.77,ammonium nitrogen 3.533-4.800 ?g/g,effective potassium 13.671-39.333 ?g/g,total nitrogen 0.05-0.11 mg/g,organic matter 5.44-9.02 mg/g.The soil enzyme activity is 0.004-0.011 phenol mg/g for acid phosphatase,0.002-0.006 phenol mg/g for neutral phosphatase,and 0.008-0.033 phenol mg/g for alkaline phosphatase.Based on the above results,it can be found that the rhizosphere soil of the four plants are extremely deficient in ammonium nitrogen and total nitrogen,and the soils are weakly alkaline and the poor soil.2.Separation and screening of selective medium showed that the number of microbial colonies in the soil was 7.33-10.57×105 CFU/g,actinomycetes 1.70-7.83×105 CFU/g,fungi 0.50-1.50×105 CFU/g.It can be found that there are significant differences in the number of bacteria and actinomycetes among different plant rhizospheres.3.A total of 35 strains of nitrogen-fixing bacteria with rapid growth rate and complete colony morphology were obtained.Most strains could grow on medium with a pH of 12 and NaCl concentration of 4%,which proved that these strains have strong salt and alkali resistance as well as high environmental adaptability.4.A total of 25 strains of phosphate-producing strains with faster growth rate and more soluble phosphorus rings were screened.The amount of dissolved phosphorus was between 6.04 and 102.67 ?g/mL,and the highest amount of phosphorus was found in strain SP1 while the lowest amount of phosphorus was found in strain HP14.5.A total of 15 protease-producing strains with a faster growth rate and clear transparent circle were obtained.Among them,the ratio of transparent circle diameter(D)to colony diameter(d)was the highest in SD5,which is 3.2.And the smallest was SD6,which is 1.13,able to generate certain protease.6.Through the 16 S rDNA gene sequence analysis and identification of the excellent strains like BP4,BN5,HN7,HD3 and SD5 which can be grown in three selective mediums,this thesis found that the five excellent functional strains tested have close phylogenetic relationships with sphingomonas,Agrobatcerium tumefaciens,Arthrobacter,Fictibacillus phosphorivorans,and Bacillus simplex.7.By using 5 excellent functional strains obtained by screening to promote the growth experiment of sorghum seed,this paper found that the germination potential,germination rate,bud length and root length of sorghum seeds after soaking were higher than those of non-soaked seed.Effects are most obvious to BP4,whose germination rate is about 80%.The seeding height and fresh weight of the sorghum seedlings,which were also watered by the bacterial liquid,were increased to some extent.This proves that the functional strain had a confident promoting effect on the growth of sorghum. |
PDF Full Text Request