Optimizing copper phytoremediation and mung bean (Vigna radiata L.) yield through Sinorhizobium meliloti and Piriformospora indica inoculation

Heavy metal contamination in agricultural soil poses significant threats to ecosystem sustainability and human health. An outdoor box experiment was conducted as factorial abased on randomized complete block design, with three replications, during 2017 cropping season to evaluate the effects of biofertilizers on Vigna radiata L. growth and yield under different Cu concentrations. The first factor was fertilizer treatment including plant growth-promoting bacterium Sinorhizobium meliloti (PGP), arbuscular mycorrhizal-like fungus Piriformospora indica (AM), and chemical fertilizer (CF) and the second factor was Cu concentrations consisted of 0, 50, 100, and 200 mg _Cu/kg _soil. The greatest plant height (30.20 and 30.17 cm) and leaf area index (LAI) (1.64 and 1.55) were observed at 0 and 50 mg _Cu/kg _soil, particularly in CF and AM treatments. The highest Cu concentrations were found in the shoots (74.42 mg/kg) and grains (75.92 mg/kg) when using CF at 200 mg _Cu/kg _soil. The highest Cu concentration in the roots was obtained in PGP biofertilizer treatment (160.7 mg _Cu/kg _root). In all Cu concentrations, the shoot bioconcentration factors (BCF) in CF and control treatments were higher than those in PGP and AM treatments. The root BCF improved with the use of PGP and AM treatments, compared to the control. Except the CF, the translocation factor (TF) in other treatments were ˂ 1 and the highest TF was obtained in 200 mg _Cu/kg _soil (0.842) and CF (1.050) treatment. Based on the results, we concluded that high Cu concentrations reduced the mung bean yield and productivity. However, applying AM in Cu-contaminated soil showed significant potential for improving mung bean yield, reducing Cu availability, and minimizing plant uptake. Generally, compared with chemical fertilizer (CF), P. indica and S. meliloti inoculation effectively increased Cu accumulation in the roots of mung bean grown in Cu-contaminated soil.