Effects of Phosphate-solubilizing Bacteria on Maize Growth and Rhizosphere Soil Microbial Community Structure

To explore the mechanism of a phosphate-solubilizing bacteria Acinetobacter calcoaceticus on the properties of lead-contaminated soil and the diversity of microbial communities in maize rhizosphere, a pot experiment was performed with applying sterile water (CK), LB medium (T1), Acinetobacter calcoaceticus liquid culture (T2), and Acinetobacter calcoaceticus fermentation broth (T3) to the maize rhizosphere. The fixation and transfer of lead by Acinetobacter calcoaceticus in maize rhizosphere soil, and its effects on the structure and composition of microbial communities and their interactions were investigated. The results show that the application of LB medium, Acinetobacter calcoaceticus liquid culture, and fermentation broth significantly increased the nitrate nitrogen content (NO₃^--N) and acid phosphatase (ACP) activity in maize rhizosphere soil. Compared to the control, the application of Acinetobacter calcoaceticus liquid culture increased the available phosphorus (AP) and residual lead content in maize rhizosphere soil by 43.47% and 15.13%, respectively. All treatments changed the number of OTUs of soil bacterial and fungal communities and the relative abundance of dominant genera. According to the correlation analysis, the NO₃^--N content in soil was the key factor affecting the microbial community structure of maize rhizosphere soil. Compared to the control, the application of LB medium, Acinetobacter calcoaceticus liquid culture, and fermentation broth reduced the malondialdehyde (MDA) content in maize leaves, and the treatment of Acinetobacter calcoaceticus liquid culture reduced the MDA content in maize leaves by 37.65%. Meanwhile, the treatments of Acinetobacter calcoaceticus liquid culture and fermentation broth reduced the activities of superoxide dismutase (SOD) and catalase (CAT) in maize leaves; the treatment of Acinetobacter calcoaceticus liquid culture significantly increased the plant height, aboveground and belowground dry weight of maize, while decreased the lead content in leaves and roots by 78.03% and 44.07%, respectively. The application of Acinetobacter calcoaceticus bacterial solution effectively reduced the content of ion exchangeable lead in soil, increased the content of residual lead in soil, and mitigated the stress of soil lead and the uptake of lead in maize plants.