Phytoremediation effect of metal-mobilizing bacteria on growth promotion and nutrient uptake of <i>Populus deltoides</i> under controlled conditions

Plant-colonizing beneficial microbes are effective bio-tools for enhancing phytoremediation. Two-year pot experiment at Punjab Agricultural University, Ludhiana, India, assessed the response of <i>Populus deltoides</i> under nursery conditions to sewage sludge treated soil with indigenous metal-mobilizing <i>Bacillus</i> species-<i>B. thuringiensis</i> (T₁), <i>B. cereus</i> (T₂), <i>B. pumilus</i> (T₃), and their consortium (T₄), with three inorganic fertilizer levels-RDF1-100%, RDF2-75%, and RDF3-50% [Recommended dose of fertilizer (RDF)]. Each inoculated treatment was compared to its respective uninoculated control (C). The application of T₄ with RDF1 significantly increased shoot length and biomass by 13.8 and 32.9% than C, respectively. Bioconcentration factors (BCF) for Cd and Ni increased by over 50% than C demonstrating enhanced phytoremediation efficiency. Elemental accumulation was predominantly localized in roots, with the exception of Zn and Cd. Among most of the parameters, RDF1 × T₄ was statistically comparable with RDF2 × T_4. Irrespective of fertilizer dose, T₄ maximally improved phytoremediation efficiency (BCF) by 0.61 (shoot) and 0.52 (root) compared to 0.20 and 0.16 in C, respectively, as well as soil chemical and biological properties up to 22.3%. These results highlight the potential of indigenous microbial inoculants to reduce soil heavy metals and enable sustainable, enhanced phytoremediation with 25% lower fertilizer input.