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Novel phosphate-solubilizing bacteria enhance phosphorus uptake and growth in Populus nigra under P-deficient soils
Samaneh Samavat1, Mahdiyeh Salehi Vozhdehnazari1, Fatemeh Keneshloo1
1Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Tehran 14968-13111, Iran.
Aims:
Phosphorus (P) is an essential macronutrient, but in many alkaline and acidic soils it is immobilized in insoluble forms, restricting plant uptake. Such limitations are particularly problematic for Populus nigra, a fast-growing tree widely used in forestry and ecological restoration. This study aimed to assess whether novel phosphate-solubilizing bacteria (PSB) can enhance P availability, nutrient uptake, and growth performance of P. nigra Clone 154.62 under P-deficient conditions.
Methods And Results:
Three PSB strains isolated from black poplar rhizospheres-Enterobacter hormaechei subsp. xiangfangensis FREX4, Pantoea dispersa FRPD12, and Pantoea stewartii subsp. stewartii FRPS6-were evaluated through in vitro solubilization assays, biosafety tests, and outdoor inoculation trials. FREX4 and FRPD12 efficiently solubilized tricalcium phosphate (355 and 368.1 µg mL-1), while FRPS6 showed higher activity on hydroxyapatite (66.5 µg mL-1). Inoculation significantly improved seedling height, biomass, and chlorophyll content, with FREX4 consistently producing the greatest effects. Plant P concentration nearly doubled relative to the control (0.39% vs. 0.21%), and available soil P increased from 3.66 to 12.8 mg kg-1. Root colonization assays confirmed superior rhizosphere competence of FREX4. Biosafety analyses indicated that FREX4 and FRPD12 were safe for application, whereas FRPS6 retained virulence traits despite its solubilization ability.
Conclusions:
PSB inoculation improved P acquisition, plant growth, and soil fertility, with FREX4 identified as the most effective and safe biofertilizer candidate for forestry use.
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