PGPR inoculation of a contaminated soil affects plant growth and phytoavailability of Cd and Pb

Abstract

ABSTRACT To evaluate the effects of cabbage varieties and PGPR inoculation on the mobility and phytoavailability of Pb and Cd in a contaminated soil, a factorial (3 × 6) pot experiment with completely randomized design and three replications was performed. The cabbage varieties were ornamental cabbage, broccoli and cabbage and the PGPR strains included Pseudomonas putida PTCC1694, Bacillus megaterium PTCC1656, Azotobacter chroococcum, Proteus vulgaris PTCC1079 and Bacillus subtilis PTCC1715. The results indicate that the PGPR inoculation increased the amounts of plant biomass, the Pb and Cd concentrations in the root and shoot, the Pb and Cd uptake performances, the mobility, phytoavailability and translocation factor. The Pb bound to Fe-Mn oxides (42.7%) and the Cd bound to carbonate (38.1%) were the predominant heavy metal fractions. The percentages of the Pb and Cd in the soluble, exchangeable and organic matter-bound fractions increased while those of the Pb and Cd in the carbonate and Fe-Mn oxide-bound fractions decreased by lowering the soil pH and increasing the concentration of dissolved organic carbon (DOC). It is concluded that inoculation of heavy metal contaminated soils by the PGPR strains, especially Bacillus megaterium PTCC1656, enhances the phytoremediation process by increasing the metal phytoavailability and biomass production of the plant. Abbreviations HMe: Heavy metals; PGPR: Plant growth-promoting rhizobacteria; DOC: Dissolved organic carbon; HCN: Hydrogen cyanide; IAA: Indole-3-acetic acid; MIC: Minimum Inhibitory Concentrations; LB: Liquid broth; EC: Electrical conductivity; OC: Organic carbon; FC: Field capacity; WS: Water soluble; EX: Exchangeable; CAR: Bound to carbonates; OX: Bound to Fe-Mn oxides; OM: Bound to organic matter; RES: Residual; BOA: Ornamental cabbage; BOC: Cabbag; BOI: Broccoli; Pp: Pseudomonas putida PTCC1694; Bm: Bacillus megaterium 107 PTCC1656; Ac: Azotobacter chroococcum; Pv: Proteus vulgaris PTCC1079; Bs: Bacillus subtilis 108 PTCC1715; C-: Uninoculated non-rhizosphere soil; C+: Uninoculated rhizosphere soil; TF: Translocation factor; MF: Mobility factor; ANOVA: Analysis of variance