Background and Aims <p>The activation of unavailable phosphorus in calcareous soils plays an important role in enhancing crop productivity. The aim of this study was to investigate the synergistic effects of nano titanium dioxide (nano TiO₂), phosphorus-solubilizing bacteria (PSB), and yeast peptides (YP) on soil phosphorus dynamics, plant phosphorus uptake and growth.</p> Methods <p>This study investigated the effects of low (25 μg kg⁻¹, L) and high (25 mg kg⁻¹, H) doses of nano TiO₂, combined with PSB and YP on soil phosphorus availability, pH, and phosphatase activities in calcareous soils, as well as the impact of these treatments on nutrient uptake and growth of Bok Choy.</p> Results <p>LPY and HP treatments significantly increased soil available phosphorus content, while LPY, HP, and HPY treatments significantly reduced soil pH. HP treatment notably decreased acid phosphatase (AcP) activity, and LP and all high-dose treatments significantly reduced alkaline phosphatase (AlP) activity. Moreover, all treatments (except LY) significantly decreased phosphodiesterase (PD) activity. Phosphorus uptake was increased significantly by 62.81% to 138.71% in all treatments except LY and H, whereas dry weight was enhanced 42.86% to 54.79% under LPY, HP, and HPY treatments.</p> Conclusion <p>A low dose of nano TiO₂ combined with both PSB and YP, or a high dose of nano TiO₂ with PSB alone, can effectively mobilize fixed inorganic phosphorus in calcareous soils with low available phosphorus. This activation primarily occurs through pH reduction rather than increased phosphatase activity, synergistically improving nutrient uptake and promoting Bok Choy growth.</p>