Synergistic enhancement of ryegrass-based phytoremediation for cadmium-contaminated phosphate mine soil using <i>Bacillus megaterium</i> and humic acid activator

This study investigated the combined effect of <i>Bacillus megaterium</i> (B) and humic acid activator (HA) on enhancing ryegrass phytoremediation of Cd-contaminated phosphate soil. A pot experiment compared four treatments: control (CK), B alone, HA alone, and combined B + HA. Results showed that the B + HA treatment most effectively improved the soil microenvironment, reducing pH by 0.83 units and increasing available phosphorus by 45.74% compared to CK. This combination also notably promoted ryegrass growth, increasing above-ground and root dry weight by 47.31% and 58.33%, respectively, while increased plant height and chlorophyll content. Regarding Cd remediation, B + HA increased available Cd in rhizosphere soil by 61.90% and enhanced above-ground Cd accumulation by 21.18% compared to CK. Two-way ANOVA confirmed significant interactive effects between B and HA on Cd accumulation, soil pH, and phosphorus availability. The combined treatment also increased the bioaccumulation factor and transportation factor of Cd. The study demonstrates that <i>B. megaterium</i> and HA act complementarily to improve soil conditions, promote plant growth, and enhance Cd phytoextraction efficiency in ryegrass.