Introduction
Cadmium (Cd) contamination of soils is a serious environmental concern due to its persistence, high mobility, and toxicity, posing significant risks to food security and ecosystem stability. The transfer of Cd into the food chain through contaminated crops can lead to severe human health disorders. Phytoremediation has been recognized as an environmentally friendly and cost-effective strategy for the remediation of Cd-contaminated soils. Forage sorghum (Sorghum bicolor L.) is considered a promising species for phytoremediation because of its extensive root system, rapid growth rate, adaptability to stress conditions, and high biomass production. However, its phytoremediation efficiency may be restricted by limited Cd bioavailability in soil and metal-induced growth inhibition. Biological approaches such as plant growth-promoting bacteria (PGPB), including Pantoea agglomerans and Pseudomonas fluorescens, can improve plant performance under Cd stress through mechanisms such as siderophore production, phytohormone synthesis, phosphate solubilization, and stimulation of antioxidant defense systems. Arbuscular mycorrhizal fungi (AMF) enhance root absorption capacity via extensive hyphal networks and may regulate metal distribution and stabilization in the rhizosphere. In addition, chemical chelators such as Na-EDTA can increase Cd solubility and availability for plant uptake, although their application may raise environmental concerns, including potential metal leaching. Although the individual effects of PGPB, AMF, and EDTA on Cd-contaminated soils have been widely reported, information regarding their interactive effects on forage sorghum under Cd stress remains limited. Therefore, this study aimed to evaluate the individual and combined effects of PGPB, AMF, and Na-EDTA on growth traits and Cd phytoremediation efficiency of forage sorghum grown in Cd-contaminated soil.
 
Materials and Methods
The experiment was conducted in the summer 2024 in a greenhouse at Razi University, Kermanshah, Iran, at the geographical coordinates 34°29′19″ N latitude and 47°05′53″ E longitude. Clay loam soil (pH 7.95, EC 0.435 dS m⁻¹, organic carbon 1.326%) was collected from a nearby field, air-dried, sieved (2 mm), and mixed with sand (2:1 ratio). Soil was spiked with 40 mg kg⁻¹ CdSO₄ and equilibrated for one month. A factorial completely randomized design with four replicates was applied across 48 pots (26 cm diameter, 30 cm height). Treatments included: (1) PGPB at three levels (control (no bacteria inoculation), P. agglomerans 6 g kg⁻¹ seed, Ps. fluorescens 7 mL kg⁻¹ seed); (2) AMF at two levels (control (no mycorrhizal inoculation), 30 g kg⁻¹ seed); and (3) Na-EDTA at two levels (control (zero), 3 mg kg⁻¹ soil). Seeds were inoculated with sugar-water solution (2%) for solid inoculants, followed by Ps. fluorescens, dried, and sown (10 seeds/pot, thinned to 5 plants). Na-EDTA was applied post-emergence. Irrigation was maintained at field capacity, and plants were harvested 93 days after sowing at the onset of the reproductive stage. Measured traits included aerial and root biomass (oven-dried at 80°C for 48 h), plant height, leaf area (ImageJ), Cd concentrations in plant tissues and soil (acid digestion and atomic absorption spectrometry), translocation factor (TF = shoot Cd/soil Cd), root bioconcentration factor (BCF = root Cd/soil Cd), and tolerance index (TI = treated aerial biomass/control aerial biomass). Data were analyzed using SAS 9.4 with ANOVA and Duncan’s test (P ≤ 0.05).
 
Results and Discussion
Shoot and root biomass as well as tolerance index were not significantly affected by treatments, indicating that Cd stress likely overshadowed the growth-promoting effects of biological amendments and that sorghum’s intrinsic tolerance mechanisms played a dominant role. Na-EDTA significantly increased plant height by 12% compared with the control, suggesting that chelation reduced Cd toxicity and improved growth conditions. The interaction between bacteria and Na-EDTA significantly influenced leaf area. Single inoculation with Pantoea agglomerans or Pseudomonas fluorescens (without EDTA) increased leaf area by approximately 25.5% compared with the control, likely due to enhanced phytohormone production and nutrient availability. However, the addition of EDTA reduced this positive bacterial effect, possibly because of nutrient imbalance or microbial competition. The most pronounced phytoremediation response was observed under the combined application of Pseudomonas fluorescens and Na-EDTA. This treatment increased Cd concentration in shoots by 91% and in roots by 73.8% relative to the control. Simultaneously, soil bioavailable Cd decreased by 44.7%, confirming substantial Cd extraction from the soil. The translocation factor increased more than three-fold, and root bioconcentration factor increased by 216.7%, demonstrating enhanced Cd uptake and internal transfer capacity. AMF showed limited influence on BCF but reduced Cd translocation to shoots, suggesting a stabilizing role in the rhizosphere and partial immobilization of Cd, consistent with its protective function under heavy metal stress.
 
Conclusion
The combined application of Pseudomonas fluorescens and Na-EDTA markedly enhanced Cd phytoremediation efficiency in forage sorghum by increasing Cd uptake, root accumulation, translocation to shoots, and depletion of bioavailable soil Cd. While biomass production was not significantly altered, improvements in plant height, leaf area, TF, and BCF indicate enhanced functional performance under Cd stress. Single bacterial inoculation primarily improved leaf development and physiological potential, whereas AMF moderated Cd transfer to aerial parts through rhizospheric stabilization. Overall, integrating biological inoculants with controlled chelator application represents a promising strategy for optimizing phytoremediation of Cd-contaminated soils. Future research should evaluate long-term field performance, different contamination levels, and environmental safety aspects associated with chelator use.
 
Acknowledgement
Gratitude is extended to Lorestan, Razi, and Kharazmi Universities for providing the necessary facilities and cooperation to carry out this research.