Phytoremediation potential of pot marigold ( <i>Calendula officinalis</i> L.) under plant growth-promoting rhizobacteria (PGPR) treatments for sustainable urban green infrastructure development

This study evaluated the phytoremediation potential of pot marigolds on green wall systems for removing soil cadmium. The experiment was a factorial arrangement in a randomized complete block design. The first factor was cadmium (0, 1, 2, and 3 mg/kg soil), and the second was seven single or mixed plant growth-promoting rhizobacteria (PGPR) and the control treatments. All root and flower-related traits significantly increased after bacterial treatments (<i>p</i> ≤ 0.05). Substrates inoculated with <i>Thiobacillus thioparus</i> strain 300, Mix2 (<i>Aztobactor chorococcum</i> strain D0941 + <i>Azosporillum liposferum</i> strain So131), and Mix3 (<i>Thiobacillus thioparus</i> strain 300+ <i>Pseudomonas putida</i> strain G0951+ <i>Aztobactor chorococcum</i> strain D0941+ <i>Azosporillum liposferum</i> strain So131) increased phytoremediation of pot marigold in roots and shoots up to 3 mg/kg soil cadmium. The transfer factor (TF) was under one in flowers, showing the low potential of the flowers for phytoremediation. TF was above one in aerial vegetative plant sections, indicating the species as a cadmium accumulator and extractor for managing cadmium contaminant sites. Based on purification ratios and transfer factors, <i>Thiobacillus thiolates</i> (alone or combined) is recommended for enhancing pot marigold esthetics in landscapes, while Pseudomonas strains (single or mixed) improve its phytoremediation potential in urban green infrastructure.