Plant Growth-Promoting Rhizobacteria (PGPR) and Phosphorus Fertilizer-Assisted Phytoextraction of Toxic Heavy Metals from Contaminated Soils

Phytoremediation is a remediation technique that involves the use of plants to extract, sequester, and/or detoxify pollutants through physical, chemical, and biological processes. The use of phytoremediation is expanding due to its cost-effectiveness compared with conventional methods. This study was conducted to investigate the effects of autumn and spring application of plant growth-promoting rhizobacteria (PGPR, 10⁸ cfu mL^?1 Bacillus megaterium var. phosphaticum sprayed at 250 mL plot^?1) and phosphorus (P) fertilizer (0, 11, 22, 33, 44 kg P ha^?1) on dry matter yield and heavy metal uptake by plants in soils contaminated with heavy metals. Field experiments were conducted using a randomized complete block design with four replications between 2004 and 2007. The results of the study indicated that P fertilization, but not PGPR application, significantly affected dry matter yield. Application of PGPR increased heavy metal availability in soils and the heavy metal uptake of meadow plants. The heavy metal content of the meadow plants resulting from PGPR application was 4–6 times higher for the spring application than the autumn application. Approximately 16, 30, 10, 10, and 3 growing seasons without PGPR are necessary to remove all lead (Pb), nickel (Ni), boron (B), manganese (Mn), and zinc (Zn), respectively, from polluted soil. The time required for Pb, Ni, B, Mn, and Zn removal could be further decreased to approximately 4, 6, 3, 3, and 1 growing seasons, respectively, with 33 kg phosphorus pentoxide (P₂O₅) ha^?1 and 10⁸ cfu mL^?1 PGPR applications at rates of 250 mL plot^?1 in the spring season.