Fig. 7

Promotion of Solanum lycopersicum L. cv. Micro Tom growth by biochar-immobilized phosphorus-solubilizing bacteria. A The survival rate of the NK2-GFPuv strain in the soil was assessed after 0, 15, and 30 days of applying phosphorus-solubilizing bacteria immobilized by cotton straw biochar. Soil pH values (B) and available phosphorus contents (C) were measured after 0, 15, and 30 days. Chlorophyll content (D), plant height (E), above-ground fresh weight (F), above-ground dry weight (G), underground fresh weight (H), underground dry weight (I), root tips (J), root length (K), and root surface area (L) of tomato plants were recorded after 15 and 30 days of growth. CK indicates untreated soil. CBC indicates the rhizosphere soil treated with cotton straw biochar alone. UPB indicates the rhizosphere soil treated with unimmobilized phosphorus-solubilizing bacteria (NK2-GFPuv alone) and IPB indicates the rhizosphere soil treated with immobilized phosphorus-solubilizing bacteria by cotton straw biochar. 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