Screening and identification of an efficient phosphate-solubilizing Burkholderia sp. and its growth-promoting effect on Pinus massoniana seedling

Abstract

We isolated phosphate solubilizing bacteria (PSB) from the rhizosphere soil of P. massoniana by the standard dilution plating technique, and determined the phosphate solubilizing characteristics of PSB by the Molybdenum antimony resistance colorimetric method. We explored the mechanism of phosphorus dissolution through analysis of the relationship between the phosphate-solubilizing ability of PSB and the pH of the fermentation broth and the determination of organic acids in the fermentation broth by HPLC-MS. The effects of PSB on the growth and physiology of P. massoniana were clarified by measuring the growth, physiology, soil nutrients, and soil enzyme activity of potted P. massoniana seedlings inoculated with PSB. The results showed that 16 strains of PSB were screened from the rhizosphere of P. massoniana. Among those strains, WJ27 had the best effect of solubilizing phosphorus, with the amount of phosphate solubilized reaching 411.98 mg·L-1 after five days of liquid culture. The strain was identified as Burkholderia sp. by phenotype observation, physiological and biochemical identification and phylogenetic tree analysis. The highest phosphate solubilizing capacity in four phosphorus sources mediums was Ca3(PO4)2(220.85 mg·L-1) > AlPO4(182.33 mg·L-1) > FePO4·2H2O (129.19 mg·L-1) > CaHPO4·2H2O (115.23 mg·L-1). WJ27 could reduce the pH of fermentation broth by secreting organic acids, such as citric acid and malonic acid, which contribute to phosphorus solubilization. Results from pot experiments showed that WJ27 had positive effects on the growth, physiology, soil nutrients, and soil enzyme activities of P. massoniana seedlings. Compared with the control, seedling height, main root length, total lateral root number, shoot (stem, leaf and branch) fresh weight, shoot dry weight, root fresh weight and root dry weight of P. massoniana inoculated with WJ27 increased by 14.3%, 36.9%, 56.1%, 44.7%, 60.0%, 158.3% and 100.0%, respectively. Chlorophyll b, total chlorophyll, shoot soluble protein, shoot soluble sugar, root activity, and root soluble protein increased by 145.8%, 45.2%, 206.3%, 59.4%, 80.5% and 260.0%, respectively. The SOD and POD acti-vities of root, and CAT activities of shoot of P. massoniana seedlings increased by 71.2%, 197.5% and 36.6%, respectively. Contents of available N, available K, available P, urease, catalase and phosphatase increased by 18.1%, 17.0%, 11.9%, 34.3%, 45.5%, and 62.6%, respectively. Burkholderia sp. WJ27 could improve soil nutrient concentrations and enzyme activities and thus facilitate the growth of P. massoniana seedlings.