The effect of cadmium, zinc, and copper on the growth, tolerance index, metal uptake, and production of malic acid in two strains of the grass Festuca rubra

Abstract

The effect of zinc, cadmium, and copper on the growth, tolerance indices, and metal uptake of Merlin Festuca rubra from Trelogan mine, Wales, and Cascade Festuca rubra, a normal grass, were investigated by growth experiments in metal amended nutrient solution. The effect of zinc or copper on the malic acid concentration in both strains was also investigated. Fresh weight was shown to be a good indicator of growth for experiments over a 28-day period. Using a parallel method to calculate tolerance indices, the Merlin strain was significantly more tolerant to 50.0 mg L−1 Zn (P = 0.005), 1.0 mg L−1 Cd (P = 0.004), and 1.0 mg L−1 Cu (P = 0.012), compared with Cascade. The upper critical tissue concentrations showed that Merlin could withstand twice as much zinc and 12 times the amount of cadmium in its shoot tissue before the onset of toxicity, compared with Cascade. However, the levels for copper were similar for both strains. The carboxylic acids present in both Cascade and Merlin were qualitatively identified using high performance liquid chromatography. The concentration of malic acid present in the shoot tissue of each strain was determined and showed that Merlin contained a greater amount of malic acid compared with Cascade and that the levels increased on exposure to zinc, but not with copper. Keywords: metal tolerance, Festuca rubra, malic acid, high performance liquid chromatography (HPLC), upper critical concentrations.