Phytotoxic Responses of Agricultural Crops to Nickel–Cobalt–Manganese Exposure During Early Growth Under Neutral and Acidified Conditions

The rapid expansion of nickel–cobalt–manganese (NCM) battery production has raised concerns regarding mixed‐metal contamination in agricultural ecosystems, particularly in regions lacking effective end‐of‐life battery management. Such contamination may promote uncontrolled metal release and pose phytotoxic risks during early crop establishment. Unlike single‐metal exposure, this represents a complex mixed‐metal stressor whose combined biological effects and modulation by chemical conditions remain insufficiently understood. Here, we investigated early plant responses using four widely cultivated crops—maize ( Zea mays ), wheat ( Triticum aestivum ), canola ( Brassica napus ), and Chinese cabbage ( Brassica rapa subsp. pekinensis )—under non‐acidified and acid‐amended conditions. Two experimental regimes were applied: a non‐acidified gradient (0–500 mg·L −1 ) and an acid‐amended scenario simulating battery‐derived leachates (200–1000 mg·L −1 ). Across species, germination processes were relatively resilient to metal exposure, whereas post‐germination traits—including root and shoot growth, root–shoot allocation, photosynthetic pigment stability, antioxidant responses, and biomass accumulation—were more sensitive and exhibited clear inhibitory responses. Acidification transiently enhanced early performance at low stress levels but markedly amplified phytotoxic effects at higher concentrations, indicating a limited capacity for physiological adjustment under increasing exposure. Plant responses were strongly species‐specific, with wheat showing the highest tolerance, maize intermediate plasticity, and canola and Chinese cabbage greater sensitivity. Overall, phytotoxicity was chemically mediated, concentration‐dependent, and species‐specific, with root‐related traits representing critical bottlenecks for early crop performance under mixed‐metal exposure.