Metal Accumulation And Physiological Responses Of Bamboo-willow (Salix Sp.) To Heavy Metal Stress

As anemerging method for remediation of soils contaminated by heavy metals,phytoremediation has increasingly caught the attention because of its high effectiveness,low cost,easy implementation and eco-friendly nature.Bamboo-willow(Salix sp.)has the potential to be used as candidate for phytoremediation becauseit has a high growth rate and biomass yield,strong and well-developed roots,versatile timber material and low risk to contaminate human food chain.In the present study,hydroponic and pot experiments were conducted to investigate the accumulation and translocation of heavy metals and other physiological responses of bamboo-willow plants to heavy mental stress.The main results are summarized below.1.A hydroponic experiment was conducted to evaluate the effect of cadmium(Cd)treatments(0,5,10,50 ?mol L-1 Cd)on bamboo-willow growth.The Cd uptake and translocation in the plants were also investigated.It was found that bamboo-willow exhibited a high tolerance to Cd toxicity.Higher Cd concentration(50 ?mol L-1)treatment did not inhibit the growth rate of the bamboo-willow.The content of chlorophyll a and chlorophyll b decreased,but their ratio increasedunder Cd stress.Among the plant tissues,the roots had the highest bio-concentration factor(BCF),followed by the phloem.Values of the translocation factor of all the plant tissues wereless than 0.5.Cd accumulation in the aboveground parts of the bamboo-willow accounted for 47-77% of the total Cd content in the bamboo-willow plant.2.A pot experiment was carried out to investigate the physiological responses of bamboo-willow to heavy metal stress and associated mechanisms.Two bamboo-willow cultivars,bamboo-willow III and bamboo-willow V were grown in two soils,including an uncontaminated soil(the control)and a contaminated soil taken from land near a copper smelter.The contaminated soil contained high concentrations of Cd,copper(Cu)and zinc(Zn).The effect of heavy metal stress on the concentrations of Chlorophy II(Chl)and Carotenoid(Car),soluble sugar(SS),proline,soluble proteins(SP)and malondialdehyde(MDA),and activities of peroxidase(POD)and superoxide dismutase(SOD)in the bamboo-willow plants were evaluated.It was found that the concentrations of Chl,Car,SS and SP in the leaves of bamboo-willow grown in the contaminated soil were significantly lower than those in the control.However,the concentrations of free proline,POD and SOD in the leaves of the bamboo-willow grown in the contaminated soil were significantly higher.In the contaminated soil treatment,concentrations of the free proline,SP,SOD in the bamboo-willow III leaves were significantly lower than that of bamboo-willow V,whereas concentrations of Chl b and POD in the leaves of bamboo-willow V were higher.In the control,concentrations of SS,SP,POD and SOD in the leaves of bamboo-willow III were significantly lower than those of bamboo-willow V,except the Chl concentration,which was higher than that of bamboo-willow III.There was no significant difference for the chlorophyll a/b ratios,and concentrations of chlorophyll b and MDA between the two bamboo-willowcultivars.Therefore,bamboo-willow has the potential to be used forphytoremediation of contaminated soils because of its effectiveness in uptake and accumulation of heavy metals in plants.Concentrations of Chl,Car,SS and SP may be used as indicators of heavy metal tolerance of bamboo-willow plants.The leaves of bamboo-willow V maintained higher concentrations of SS,SP,POD and SOD than those of bamboo-willow III grown in the contaminated soil,indicating that bamboo-willow V was more tolerant to heavy metal stress than bamboo-willow ?.