[Characteristics of cadmium tolerance and bioaccumulation of Bidens pilosa L. seedlings].

Bidens pilosa L. has been identified as a newly found Cd-hyperaccumulator. In the present study, the characteristics of its Cd tolerance (growth response and physiological and biochemical characteristics) and accumulation were examined. The results showed that low Cd treatments (< or =32 mg/kg) could enhance plant growth, the dry biomass of shoot and root increased by 32.4%-44.7% and 29.1%-57.6%, respectively, at Cd concentrations 8-32 mg/kg when compared with the control. The shoot dry biomass reached a maximum of 0.22 g/pot at a concentration 8 mg/kg of Cd. Meanwhile, under different Cd treatments, chlorophyll (Chl) and soluble protein contents in leaves slightly decreased, resulting in 23.3% and 41.5% reduction, respectively, compared with the control. The activities of superoxide dismutase (SOD) firstly decreased and then increased with increasing Cd concentration. Peroxidase (POD) activities and malondialdehyde (MDA) contents increased with increasing Cd concentration, with 1.2-6.6 and 1.1-1.5 times increase, respectively, relative to the control. However, the definite negative effects on the plant growth and characteristics of physiology and biochemistry were observed at higher Cd concentrations (50-100 mg/kg). In gradual experiments, the values of bioaccumulation and translocation were more than 1.0, furthermore, the concentration of Cd in shoots reached 119.1 mg/kg at the soil Cd level of 100 mg/kg, showing B. pilosa has the basic characteristics of a Cd-hyperaccumulator. The results above indicated that B. pilosa has strong capacity of Cd tolerance and accumulation, so it has potential and valuable application to phytoremediation of contaminated soils by Cd.