Screening and characteristics of phosphorus solubilizing bacteria in the rhizosphere of Parashorea chinensis plantation

  Objective  The Parashorea chinensis is an endemic and endangered species in China, and it is classified as a class Ⅰ protected wild plant. Plantation cultivation is an important means to expand its populations. Phosphorus (P) supply is a major influence on tree growth and development, and P dissolving bacteria plays an important role in P transformation. This research aimed to screen high-efficient phosphate-solubilizing bacteria (PSB) from the rhizosphere soil of P. chinensis plantations of different ages, and explore its P-solubilizing characteristics, so as to provide bacterial resources and culture conditions for the development of microbial fertilizer suitable of P. chinensis.

  Method  (1) PSB was isolated and screened from the rhizosphere soil of P. chinensis in different ages by inorganic P solid medium. The physiological and biochemical tests and 16S rDNA gene sequence were used to further identify 4 strains of PSB. (2) The relationship between the amount of P dissolved by PSB and the pH of the bacterial solution was studied by detecting the dynamics of P solubilization. (3) A single factor experiment was conducted to investigate the P-solubilizing characteristics of high efficiency PSB under different environmental and nutritional factors.

  Result  (1) A total of 18 strains of phosphorus solubilizing bacteria were isolated and screened, and the 4 strains with the strongest P-solubilizing capacity were P4, P8, P12 and P30 (P-solubilizing capacity was 552.87, 559.78, 548.53 and 598.89 mg/L, respectively). (2) Strain P8 was identified as Burkholderia gladioli, P4 and P12 as Burkholderia cepacia, and P30 as Bacillus cereus by physiological, biochemical identification and combined with phylogenetic tree analysis. (3) There was a highly significant (P < 0.01) negative correlation between the pH of the cultures and the amount of phosphorus dissolved by the P4, P8, P12 and P30 strains, with correlation coefficients of −0.995, −0.990, −0.985 and −0.997, respectively. (4) The results of single factor test showed that the PSBs had the preferable P-solubilizing effects at a temperature of 30−35 ℃, the pH of 5.5−8.5, the NaCl mass fraction was 0−2.5%, the carbon (C) sources were sucrose, lactose and glucose, and the nitrogen (N) sources were ammonium oxalate and ammonium sulfate. The optimal C∶N of strain P30, P12 and P4 was 20∶1, and that of P8 was 40∶1. The optimal P source for strain P12 was FePO₄, and Ca₃(PO₄)₂ for P30, P8 and P4.

  Conclusion  The P-solubilizing ability of PSBs can be significantly affected under different culture conditions. The 4 strains of high efficiency PSB have preferable P-solubilizing ability, which can dissolve a variety of insoluble inorganic phosphates. Therefore, it is expected to provide germplasm resources for the development of high-efficiency microbial phosphate fertilizers with a good application potential.