Effect of Plant Growth Promoting Pseudomonas on Copper Phytoremediation by some Indigenous and Crop Plants

Remediation of heavy metals contaminated soils by plants is one of the most cost-effective and environmentally friendly methods. In some cases, useful soil microorganisms are used to increase the plants efficiency in heavy metal remediation. The aim of this study was to investigate the effect of rhizospheric pseudomonads on increasing the phytoremediation efficiency in copper (Cu)-contaminated soils. The first experiment was carried out in a completely randomized design in three replications with 11 plant treatments (Maize (Zea mays), sorghum (Sorghum bicolor), wheat (Triticum aestivum), canola (Brassica napus), Fennel (Foeniculum vulgare), Amaranth (Amaranthus), Salvia (Salvia officinalis), Zygophyllum (Zygophyllum), Ajwain (Trachyspermum ammi), alfalfa (Medicago sativa) and pumkin (Cucurbita)). The highest Cu concentration and uptake  were related to Zygophyllum with 173 mg kg-1 and pumkin with 222 µg pot-1, respectively. Five plants including pumpkin, maize, wheat, canola, and Zygophyllum were selected based on the highest Cu concentration and uptake of  for the second experiment. The second experiment was designed in a completely randomized design with two factors including plant types at five levels (pumkin, maize, canola, wheat and Zygophyllum) and three levels of bacteria (non-bacterial inoculation, Pseudomonas putida PA2 strain, Pseudomonas fluorescence PA3) in three replications. In this section, the shoots and roots dry weight; Cu concentration and uptake in shoots and roots, as well as the chemical changes of the Cu in the rhizosphere were investigated. The use of both strains of the bacteria significantly increased the dry weight, concentration and uptake of Cu in shoots and roots compared to the control. Among the plants, pumpkin had the highest uptake of Cu in shoots due to high biomass (90.2 µg pot-1) (the most effective in phytoextraction) and maize due to its high root weight had the highest Cu uptake (428 µg pot-1) (effective in high Phytostabilization). Investigation of the chemical forms of Cu in the rhizosphere showed that inoculation by PA2 and PA3 growth-promoting bacteria increased 41.9 and 37% of soluble and exchangeable forms of Cu respectively, and decreased the residual form of copper up to 7.05 and 6.41%. The overall results showed that the growth-promoting bacteria play an effective role in increasing the phytoremediation, especially the phytoextraction and pumpkin with the highest Cu uptake was the most efficient plant in the Cu phytoremediation in this study.