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Five isolates from soil and nodule of legume were selected by
planting maize inoculated with phosphate-solubilizing bacteria
in vermiculite to investigate the ability of solubilization
inorganic phosphates , the kind of the organic acid in celll
excreta and resistance of antiboitics. Next, treatments
of different materials- (1)blank, (2)tricalcium phosphate,
(3)tricalcium phosphate and humic substance,(4)
tricalcium phosphate, humic substance and glucose- with
maize were used to investigated the change of
population of phosphate-solubilizing bacteria in rhizoplan and
the effect on the growth of maize.
The result of selecting test showed there were five strains -
phosphate-solubilizing bacteria from soil Bacillus pumillus
Ca20, Bacillus pumillus Ca48 and Pseudomonas cepacia PSB ,
Rhizobium fredii SB651 and Rhizobium legueminosarum biovar
trifolii V12, which seemed to express better abilities in
solubilizingtricalcium phosphate and promoting the dry weight of
maize in vermiculite. While incubating with tricalcium
phosphate liquid medium for 96 hours, the content of
water - soluble phosphorus and population of phosphate-
solubilizing bacteria increased as pH decreased for 3~4
units. The supernatant of achieved the lowest pH of 3.8.
Result in testing the resistance of antibiotics showed the five
isolates can resist teracycline on the concentration of 50 (g
mL-1 . So tetracycline were chose to add into tricalcium
phosphate plate medium as a method to affirm five isolates
besides clear one . Different organic acid and amounts of
excreta of five phosphate- solubilizing bacteria were found
by analysis of HPLC . Citric acid found in excreta of
Pseudomonas cepacia PSB may relates to the mechanism of
phosphate solubilizing and decrease of pH in
tricalcium phosphate.
Planting maize with five different inoculations and four
different treatment of materials by sand culture-(1) blank (2)
tricalcium phosphate (3) tricalcim phosphate and humic
substances, (4) tricalcim phosphate, humic substances
and glucose. During five week, the population of
phosphate - solubilizing bacteria in the rhizosphere of
maize decrease as time increase. The population of
phosphate-solubilizing bacteria remained at 105~107 CFU g-1
fresh root . The results indicate there were still
phosphate-solubilizing bacteria existing in the rhizosphere of
maize. Results in analysis of plant and soil showed treatments
of materials and inoculations were not significantly
related to phosphorus content of plant, available
phosphorus in soil, nitrogen content of plant, dry weight of
plants and dry weight of roots. But some inoculations,
Rhizobium legueminosarum biovar trifolii V12 and Rhizobium
fredii SB651, showed difference on phosphorus content of plant,
available phosphorus in soil, nitrogen content of plant. So
Planting maize in sand with inoculations of phosphate-
solubilizing bacteria for five weeks showed no significant
difference on the growth of maize in this experiment. But
individual result in phosphorus content of plant,
available phosphorus in soil, nitrogen content of plant, dry
weight of plants and dry weight of roots showed the
potential of phosphate-solubilizing bacteria in promoting growth
of maize. Further, dry matter yields in sterile soils less
than those in non-sterile soils indicated that sterile soils
would depress the growth of maize.
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