Growth and Metal Partitioning of the High-Biomass Grass Cultivar Minmu 6 Under Graded Cadmium and Lead Exposure

Phytoremediation requires plants that combine high biomass production with tolerance to metal stress. The responses of Pennisetum americanum (L.) Leeke × Pennisetum purpureum Schumach. ‘Minmu 6’ were evaluated in separate pot experiments with Cd at 0 (CK), 1.5 (L-Cd), 10 (M-Cd), and 25 mg kg−1 (H-Cd), and Pb at 0, 600 (L-Pb), 1200 (M-Pb), and 1800 mg kg−1 (H-Pb). Growth, physiological traits, and organ-level metal concentrations were measured at 45, 90, and 135 d. Mantel tests explored associations among exposure conditions, tissue metal concentrations, and plant traits. Under the selected exposure regimes, Cd-treated plants showed larger reductions in shoot growth than Pb-treated plants. Both metals were concentrated in roots, with lower shoot-to-root concentration ratios for Pb than for Cd. At 135 d, whole-plant metal removal efficiencies at the highest Cd and Pb addition rates were 1.29% and 0.21%, respectively. These values include root-associated metal and therefore exceed the fractions potentially removable through shoot harvesting alone. The observed partitioning patterns identify shoot Cd removal and root-associated Pb retention as priorities for further evaluation; they do not establish distinct remediation functions. Practical performance remains to be tested in aged contaminated soils and field experiments, with direct measurements of harvestable metal removal and soil metal mobility.