Species-level variation in cadmium phytoextraction efficiency and growth response of Brassica species inoculated with Bacillus strains.

Elevated cadmium (Cd) contamination in agricultural soils threatens ecological health and food security. This study evaluated synergistic potential of four Brassica species (Brassica juncea, Brassica carinata, Brassica napus, and Brassica rapa) combined with two Cd tolerant, plant growth-promoting (PGP) Bacillus strains (Bacillus tequilensis and Bacillus zhangzhouensis) for the restoration of Cd spiked soil. A 90-day pot experiment arranged in a randomized complete block design showed that Cd stress markedly reduced plant growth, while bacterial inoculation particularly with B. tequilensis, significantly improved biomass, chlorophyll content, antioxidant activity, and reduced oxidative stress indicators (MDA, H2O2). Among species, B. napus demonstrated highest shoot and root biomass (18.89 g FW, 0.34 g DW, and 1.40 g FW, 0.21 g DW), and elevated Cd accumulation (BAF = 0.98, TF = 1.90). Phytoextraction efficiencies were graded as (1) B. napus (77%), (2) B. juncea (68%), (3) B. rapa (67%), and (4) B. carinata (62%). B. napus showed the highest phytoextraction efficiency, exceeding B. juncea, B. rapa, and B. carinata by 9%, 10%, and 15%, respectively. Soil enzymes and physicochemical properties improved with inoculation. These findings highlight B. napus inoculated with B. tequilensis as a viable option for restoring Cd-contaminated soils. Further, field scale validation is recommended.