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

This study investigated the combined effect of Bacillus megaterium (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 B. megaterium and HA act complementarily to improve soil conditions, promote plant growth, and enhance Cd phytoextraction efficiency in ryegrass.