Fig. 5

Available phosphorus content and extracellular organic acid detection of different biochars immobilizing phosphorus-solubilizing bacteria Pseudomonas sp. NK2-GFPuv in NBRIP medium. A The available phosphorus content of immobilized NK2-GFPuv by no carrier, pinewood, cotton straw, wheat straw, maize straw, coconut shell, rice husk, and peanut shell in the culture of 0 h, 12 h, 24 h, 36 h, 48 h, 72 h, 96 h, and 120 h. No carrier indicates that NK2-GFPuv is unimmobilized by any biochars. Bars indicate one standard deviation (SD) from the mean (n = 3), while asterisks indicate significant differences (P < 0.05) derived from a two-way ANOVA in conjunction with Dunnett’s multiple-comparison test in comparison with the available phosphorus content of different biochar treatments at the same time points. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001; no asterisks indicate no significant differences. B Types and concentrations of organic acids and the proportion of carboxylic acids at 48 h. The bottom bars show the type and concentration of extracellular organic acids, while the top pie chart illustrates the proportion of monocarboxylic, dicarboxylic, and tricarboxylic acids in organic acids. No carrier indicates that NK2-GFPuv is unimmobilized by any biochars