Effects of Combined Pb and Cu Pollution on the Growth and Activities of Plant Antioxidant Enzymes and Rhizospheric Soil Enzymes of Miscanthus floridulus

Phytoremediation of mine wastes is a promising approach for the restoration of contaminated soils. Miscanthus floridulus is a perennial herbaceous grass with high productivity and tolerant to a variety of heavy metals. Sixty-day pot experiments were carried out to investigate the effects of combined Pb-Cu contamination on some physio-biochemical markers of M. floridulus and rhizospheric soil enzyme activities. M. floridulus was tolerant to a combination of 200 mg kg-1 Pb and 100 mg kg-1 Cu stress as indicated by invisible foliar injury, increased contents of photosynthetic pigments (increased by 17.2% to 22.8% compared to the control), enhanced accumulation of soluble sugar contents by 33.5% to 52.8% in response to all treatments except the Pb100Cu50, decreased contents of malondialdehyde by 5.18% at 100 mg kg-1 Pb and 50 mg kg-1 Cu. As a response to combined Pb-Cu stress, the antioxidant enzymes (catalase, peroxidase and superoxide dismutase) activities in M. floridulus were reduced by any of the Pb-Cu treatments used in the present study. Although the growth parameters such as plant height, root number, maximal root length, and the dry biomass of aboveground parts and root were all lowered by Pb-Cu treatments, the rhizospheric soil invertase, catalase, urease and phosphatase enzyme activities of M. floridulus kept increasing when the concentration of Pb and Cu below 400 mg kg-1 Pb and 200 mg kg-1 Cu.