Fig. 1
Phosphorus-solubilizing bacterium, Pseudomonas sp. NK2, effectively solubilized phosphorus by releasing organic acids to lower pH. The available phosphorus content and pH values of NK2 in insoluble phosphorus sources FePO4 (A), AlPO4 (B), and Ca3(PO4)2 (C) were measured at day 0, day 1, day 2, day 3, day 4, and day 5. D The available phosphorus content and pH values of NK2 in (NH4)2SO4, NH4Cl, NaNO3, and KNO3 solutions were determined after 2 days of culture. E The pH values of CK (uninoculated bacteria) and NK2 were monitored under soluble phosphorus (KH2PO4) and insoluble phosphorus (Ca3(PO4)2) conditions for 0, 1, 2, 3, 4, and 5 days. Bars correspond to one standard deviation (SD) from the mean (n = 3), while different letters above columns indicate significant differences (P < 0.05) among samples at different time points for available phosphorus contents and pH values according to a one-way ANOVA in conjunction with Tukey’s multiple-comparison test. F The total titratable acids in NK2 fermentation broth under soluble phosphorus and insoluble phosphorus culture were quantified for 1, 2, 3, 4, and 5 days. CK designates the control with NK2 inoculated into LB medium. P represents available phosphorus contents and pH indicates pH values. Bars correspond to one standard deviation (SD) from the mean (n = 3), while different letters above columns indicate significant differences (P< 0.05) among samples at the same time points under different treatments according to a one-way ANOVA in conjunction with Tukey’s multiple-comparison test