Because of the undesirable effects of lead on soil properties and human health, evaluation of its remediation methods seems to be essential. In order to evaluate the effect of humic acid (HA) on the decontamination of lead (Pb) spikedsoils in the presence of wormwood plant (Artemicia absantium), an experiment was carried out in a completely randomized block design with three replications. Experiment factors including different concentrations of Pb (Pb(NO3)2 in the solid form) (0, 250, 500 and 1000 mg kg-1) and levels of HA (0, 100 and 200 mg kg-1) were considered. At the end of the growing period of plants, some soil and plant properties were measured. According to the results, BR, MBC, root and shoot dry weights, RWC and Fe and Zn concentrations in the shoot were decreased by increasing the soil Pb concentration. So, the mean values of BR and MBC in Pb1000 treatment was 60 and 51.1 percent lower than those of Pb0, respectively. Pb accumulation in the root and shoot was enhanced as a result of the increase in the soil Pb concentration. The maximum Pb concentration of shoot (37.10 mg kg-1) and root (38.1 mg kg-1) was seen in the Pb1000 treatment. Also, the results suggested that humic acid had a positive effect on the shoot of Fe, Zn and Pb concentrations. So, the concentration of these elements in HA200 treatment showed an increase 1.25, 1.64 and 1.66 times more than that of HA0, respectively. Leaf proline amount was increased significantly by elevating the soil Pb concentration; however, application of 200 mg kg-1 humic acid decreased leaf proline by 54.5 percent, as compared to the control (HA0). Therefore, humic acid effect on increasing the plant Pb uptake, improving soil biological properties, and increasing availability and dissolution of Pb showed its ability in promoting the phytoremediation efficiency. According to the obtained results of this study, woodwarm plant (Artemicia absantium) is a non-accumulator that could not be used for phytoremediation purposes.
The use of plants and soil microorganisms is a promising technique for the phytoremediation of heavy metalcontaminated soils. This study was carried out in order to evaluate the soil microbial potential with four Cd concentration levels (0, 10, 30 and 100 mg kg-1); the study also addressed the inoculation of arbuscular mycorrhizal fungi (AMF) species (a mixture of Glomus species including G. intraradices, G. mosseae and G. fasciculatum) as well as plant growth promoting rhizobacteria (PGPR) (a mixture of Pseudomonas species including P. putida, P. fluorescens, and P. aeruginosa) with the Centaurea cyanus plant. The soil sample was spiked uniformly with Cd nitrate salt to create different Cd concentrations. The contaminated soils were then sterilized and subsequently inoculated with AMF and PGPR. The results indicated that with increasing the soil Cd concentration, colonization percent, abundance of rhizobateria, shoot biomass, and shoot relative biomass were significantly decreased, while the proline content and the shoot Cd concentration were significantly increased (P≤0.05). The mean of Cd extracted in AMF and PGPR treatments was 1.8 and 2.8 and the translocation factor was 1.2 and 1.5 times higher, as compared to the corresponding control treatments, respectively. It could be concluded that microbial inoculation, in addition to improving plant growth, plays an important role in the Cd phytoremediation efficiency by plant.
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