Characteristics Of Phosphate-solubilizing Bacteria Isolated From Alfalfa And Sainfoin Rhizosphere And Its Effect On Alfalfa Growth

Isolation and screening of phosphorus-solubilizing bacteria in rhizosphere of alfalfa and sainfoin were carried out. 386 phosphobacteria strains were obtained, and among them, 137 strains showed higher phosphorus-solubilizing activity. Fine stains were selected for morphological characteristics study and determination of the strains'phosphorus solubilizing capability and the ability to produce IAA; Effect of different phosphorus-solubilizing bacteria inoculum on alfalfa was tested as well. The results obtained as follows:1. Colony of most bacteria strains was offwhite or milkiness, irregulart, translucent, processes, matt, non-pigment. All the stains do not show pigment on PKO medium, but some stains show pigmen on mongolian organic medium and pigmen diffusion, for instance LH9.2. Each stians had big difference on the ability to decomposition rock phosphate and Lecithin. The value of D/d of LH11 dissolution inorganic phosphorus higher than 2.00, which had better phosphorus solubilizing capability; The D/d of LM3, LH3, LH4, LH12 dissolution organic phosphorus higher than 2.00, which had better phosphorus solubilizing capability, for instance, the maximum phosphate solubilization capacity was 338.4 mg/ml while the minimum was 25.9 mg/ml. Some stains had grew faster, but the transparent circle little, the size of colony close to the transparent circle; Some stains had grew slow, but the diameter ratio of the transparent zone little and the size of colony reached 3.51, for instance LH4.3. There were obvious relationship between the phosphate solubilization capacity and the culture medium pH. The capability of phosphate solubilizing decreased with the increased of culture medium pH (when pH were 3.16 and 6.86, the phosphate solubilization capacity of stains LM6 and LH4 were 338.4 mg/ml and 25.9 mg/ml).4. All the strains tested had the ability to produce IAA and the ability was diferent. the concentration of it was 3.75-17.95ug/ml, the highest ability of IAA produced were strain LM18 and LH12.Three excellent stains(LM6,LH12 and LH9)had high potential for agriculture.5. five strains tested had great differences among phosphate-dissolving microorganisms' capability of dissolving rock phosphate under different calcium phosphate concentration, the maximum phosphate solubilization capacity was LM18, the phosphate solubilization capacity reached 300.0 mg/ml ,while the minimum was LH6, the phosphate solubilization capacity was 87.0 mg/ml, five strains tested were inoculated respectively after ten days later, their culture medium pH lower than that of control (7.0), decreased to 4.27-5.41. But different calcium phosphate concentration had little effect on culture medium pH of stains. In lower calcium phosphate concentration total organic acid content of stains LM18, LH12, LH6 increasing with calcium phosphate concentration increasing, total organic acid content of LS7 culture medium decreased at first and then increased, stains LS5 appeareing obvious decreased trend with calcium phosphate concentration increasing, the maximum was 9.6mmol/l, minimum was 5.0 mmol/l.6. There were obvious differences among different phosphorus-solubilizing bacteria of sensitive degree to antibiotics. The maximum resistance of the strains tested to streptomycin was 500μg/mL, but the maximum resistance of the strains tested to streptomycin was 300μg/mL.7. Colonization number of the strains tested in alfalfa root was higher than stem and leaves. Bacterial suspension dilution had obvious effect on colonization ability of stains, in different dilution the stains present different colonization ability, colonization ability of stains display generally to increase with dilution increasing, when dilution was 10-6, colonization number of stains obviously higher than the other two dilutions.8. All treatments, which inoculation different phosphorus- solubilizing bacteria inoculums, promote plant growth compared with control. Plant height, the first-cut and the second-cut, of alfalfa increase singificantly. Stem diameter of alfalfa with different phosphorus-solubilizing bacteria inoculums was obvious increase; different phosphorus- solubilizing bacteria inoculums has great influence on the dry weight/fresh weight ratio and the leaf/stem ratio of alfalfa,and compared with the dry weight/fresh weight ratio the effect of the leaf/stem ratio was more.