Phosphorus (P) availability in soils is typically low, posing a major constraint to global crop production. Polyphosphate (PolyP) fertilizers, composed of polymers of orthophosphate residues, have been proposed as alternatives to improve soil P fertility and enhance plant P acquisition. However, their effectiveness is limited by the hydrolysis of PolyP to orthophosphate (OrthoP), the form readily taken up by plants. This conversion is primarily mediated by phosphate-solubilizing bacteria (PSB) and arbuscular mycorrhizal fungi (AMF), which play complementary roles in phosphorus cycling.
This study investigated the interactions between PSB and AMF in enhancing plant P uptake from PolyP fertilizers. Field experiments were conducted with tomato, lettuce, and wheat grown in P-deficient soils, with PolyP and OrthoP applied as basal or fertigation. AMF colonization was quantified microscopically by assessing hyphae, vesicles, and arbuscule. PolyP fertigation promoted greater AMF colonization, particularly vesicle and arbuscule abundance, compared to OrthoP, and led to significantly higher yields.
Complementary PSB assays were conducted by growing bacteria on different agar media and counting colonies daily. Liquid media were used to assess hydrolysis rates through gallery assays, while bacterial growth rates were measured by the spectrometer. Results showed that bacterial growth under PolyP was highest, with No-P treatments sustaining greater counts than OrthoP. PolyP also induced stronger acid phosphatase activity and higher hydrolysis rates, resulting in elevated P concentrations compared to OrthoP and No-P.
These findings highlight the potential of harnessing PSB–AMF interactions to optimize PolyP fertilizer use, enhancing phosphorus cycling, nutrient availability, and crop productivity sustainably.
