Tolerance And Phytoremediation Potential Of Two Species Of Medicago L. On Copper Tailings

Two species of Legume, Medicago sativa L. and Medicago falcata L. were selected as the material to study the tolerance and phytoremediation potential of these two species under the stress of copper (Cu) tailing. The results are as follows:(1) The effect of different content of Cu tailings on the physiological and biochemical response of M. sativa and M. falcata seedlings were studied by pot culture. The results show that Chla, Chlb and Cx·c contents in the leaves of M. sativa under the treatment of3/4Cu tailings were the lowest; the photosynthetic pigments contents of M. falcata seedlings showed gradually decreased as Cu tailing levels enhanced. The content of O2·-in the underground part of M. sativa under1/4Cu tailing treatment was the highest and1.04times that of the control. The highest content of O2·-in M. falcalta seedlings was found under treatment of pure Cu tailings. The SOD activity of M. sativa was highest in the pure Cu treatment. The SOD activity in M. falcalta seedlings was with the trend of increased first and then decreased. CAT activity in the above-and underground part of M. sativa seedlings were the trend of increased first and then decreased. However, CAT activity in the above-and underground part of M. falcalta seedlings decreased as the increase of Cu tailing content. The AsA content of in the seedlings of two species were first increased and then decreased and the highest AsA were found under l/4Cu tailing treatment. The GSH contents in above and underground parts of M. sativa under pure Cu tailings treatment were1.20and1.06times of the control. All the GSH contents of M. falcata were higher than control and gradually increased as Cu tailing contents increased. The results indicated that SOD, AsA and GSH played an important role for the seedlings of M. sativa in the tolerance of Cu tailings and the antioxidant capacity of M. sativa was higher than that of M. falcata.(2) The effect of different content of Cu tailings on the seedling growth and Cu accumulation of M. sativa and M. falcata were studied by pot culture. The results show that the seedling heights, root lengths and dry weights of both species were lower than those of control. The seedlingheight and underground part dry weight of M. sativa under the stress of pure Cu tailing increased relatively showing that the seedling of M. sativa could accommodate the Cu tailing environment and the tolerance increased. With the increase of Cu tailing content, Cu contents in two species gradually increased and the contents in the underground parts were more than those in the aboveground parts. The translocation factors of both species under all treatments were less than1. The results indicated that M. sativa and M. falcala could adapt to the Cu tailings and the tolerant of M. sativa was higher than that of M. falcata, and both species could be used as phytostabilization in Cu tailing dam. (3) The effects of adding three kinds of organic acids into Cu tailings on the physiological and biochemical response of M. sativa and M. falcata seedlings were studied. Experimental results show that the photosynthetic pigment contents of both species decreased under all EDTA treatments and increased under the treatment of0.1mmol/kg Tc. The addition of organic acids stimulated the O2·-production in underground part of M. sativa and the contents of O2·-were higher than that in the control, while, O2·-contents in the above ground decreased in AC and Tc treatment. The SOD activities of M. sativa were lower than that of the control. Tc treatment stimulated significantly SOD activities of M. falcata and the activities of SOD were higher than that of the control. SOD activity of M. falcata was restrained by EDTA treatment. The GSH contents in the seedlings of two species under EDTA treatments were lower than the control. The GSH contents of M. sativa increased in the high concentration of AC and Tc treatment and the content of GSH of M. falcata in Tc and high concentration of AC treatment was higher than that of the control. AsA in the seedlings of M. sativa under Tc treatment were increased in a certain extent and lower Tc concentration promoted AsA production of M. falcata.(4) The effects of adding three kinds of organic acids into Cu tailings on the growth, Cu accumulation and translocation, Enrichment coefficient of M. sativa and M. falcata seedlings were studied. The results showed that under lmmol/kg EDTA treatment, the underground part dry weight of M. sativa decreased by45%compared with controls (P<0.05), and the aboveground and belowground part dry weights of M. falcata decreased by34.29%and65.85%, respectively. The effect of AC and Tc treatment on the growth of two species was not significant. EDTA treatment also significantly promoted Cu absorption and accumulation of both species. Under1mmol/kg EDTA treatment, Cu contents in aboveground and underground parts of M. sativa were162.70times and1.86times of the control, M. falcata, were15.36times and3.02times of the control. The promotion effect of high concentrations of AC and Tc on Cu accumulation of M. sativa was higher than that of low concentration of AC and Tc. The results indicated that EDTA can effectively promote the Cu accumulation and translocation, improve the enrichment coefficient, while high concentration EDTA could damage the growth of M. sativa and M. falcate. Therefore, screening suitable concentration of organic acids, especially the concentration of EDTA is very important in order to achieve the best Cu tailings and Cu contaminated environment with efficiency.