Screening Of Phosphate Solubilizing Bacteria, Optimization Of Phosphate Dissolving Conditions And Its Effect On Maize Growth

Phosphate solubilizing microorganisms could promote growth of plants, improve the available phosphorus content in soil and phosphorus uptake of plants. Phosphate solubilizing bacteria strains were screened based on conventional separation method and their adaptability to root exudates of maize in this paper. Effect on solubilization of insoluble phosphate in NBRIP culture, physiological characteristics and16S rDNA gene sequence analysis of the isolated strains, optimal culture conditions of solubilizing insoluble phosphates, pot experiments were also studied. The main results obtained were as follows:(1) Twenty strains, which could solubilize tricalcium phosphate were isolated from calcareous soils collected from Huaian in Jiangsu province. Four strains were screened based on conventional separation method and their adaptability to root exudates of maize. Strains X5, X6, Z4and Z8could grow well on solid plate and liquid culture medium which using maize root exudates as carbon source.(2) Strain X6and Z4were identified as Pseudomonas Poae and Bacillus megaterium by their morphological and biochemical characters and16S rDNA sequences. Their biological characteristics and their antagonistic abliity to soil borne pathogens suggested that they might have growth-promoting and biocontrol ability.(3) The optimal culture condition for phosphate solubilizing of strain X6were glucose (2%)、NaN03(0.15‰)、35℃, initial pH7, phosphorus source mass5g/L; While the optimal culture condition for strain Z4were glucose(1.5%)、(NH4)2NO3(0.1‰),30℃、initial pH7, phosphorus source mass5g/L. Water soluble P concentration in culture increased along with the incubation time.(4) Results of pot experiment showed that four PSBs could significantly promote the growth of maize. Under condition of no phosphorus applying, shoot height increased by5.3%～12.1%, dry weight of maize seedling by25.0%-50.6%, phosphorus accumulation in maize overground part increased by30.6%～73.2%, underground part by44.3%-104.0%. While applying phosphorus fertilizer, compared to organic fertilizer, shoot height increased by3.2%～12.0%, dry weight of maize seedling by9.6%～24.0%, phosphorus accumulation in maize overground part increased by36.5%～50.8%, underground part by14.7%～16.9%. Strain Z4had significant effect on increasing the content of available phosphorus in soil with no phosphorus applying. With phosphorus fertilizer applying, the effect on increasing the content of available phosphorus in soil was Z4> Z8> X6> X5。The colonization numbers of Z8and Z4in maize rhizosphere soil were more than that of X6and X5in pot experiment, X6was the most effective one in promotion of maize growth, strain Z4significantly increased the content of available phosphorus in soil.In summary, strains Z4had a higher potential for maize growth promotion and soil phosphorus slubilization, suggesting it could be used for further research of maize phosphorus bacterial fertilizers.