Poa pratensis Mitigates Benzo(a)Pyrene (B[a]P) and Cadmium (Cd) Co-Contamination Toxicity by Regulating Antioxidant Activity and Water-Use Efficiency

The effects of B[a]P and Cd on the growth, free-radical metabolism, antioxidants, and photosynthetic fluorescence parameters of Poa pratensis were studied by pot experiments. Results showed that low-concentration Cd (≤ 10 mg·kg^− 1) increased fresh weight, dry weight, malondialdehyde, superoxide anion radical, glutathione, and ascorbic acid. Conversely, high-concentration Cd (≥ 50 mg·kg^− 1) significantly decreased the fresh weight and dry weight, photosynthetic gas exchange, and fluorescence parameters. Water-use efficiency increased by 1.55 times compared with the control at high concentrations of B[a]P (≥ 25 mg·kg^− 1) and Cd (≥ 50 mg·kg^− 1). Principal component analysis showed that Cd played an important role in co-pollution. P. pratensis mitigated B[a]P and Cd co-contamination toxicity by regulating antioxidant activity and water-use efficiency. P. pratensis can tolerate 1, 5, and 25 mg·kg^− 1 B[a]P, as well as 1 and 10 mg·kg^− 1 Cd. P. pratensis was also highly capable of degrading B[a]P and extracting Cd in soils co-contaminated with B[a]P and Cd.