Characteristics Of Cu/Pb Tolarence And Accumulation By Elsholtzia Plants And Their Effectiveness Of Heavy Metal Removal From Polluted Water

Phytoremediation is a new technique to clean up contaminated soils by some accumulators or hyperaccumulators which can absorb exceptionally large amount of heavy metals from the environment and translocate them into shoots. The mechanisms of phytoremediation for Cu/Pb contaminated soils or water are not fully understood and the technology is not established yet. Therefore, it is important to study the characteristics of Cu/Pb tolerance and uptake by specialized plants, and the mechanisms of phytoremediation of Cu/Pb polluted soils and water. The major objectives of this study were to identify Cu/Pb tolerant and accumulating plant species and characterize their Cu/Pb uptake and tolerance, understand their potential of application to phytofiltrate Cu/Pb contaminated water. The main results obtained were summarized as follows:1. Elsholtzia splendens and Elsholtzia argyi are both dominant plants growing in Cu mining area. Solution culture experiments were conducted to study the effect of different copper levels on root morphology, photosynthesis and copper accumulation in Elsholtzia splendens and Elsholtzia argyi. The results showed that at Cu level≤50mol/L, the growth of Elsholtzia splendens was improved, but negative effects were found when Cu supply level increased from 100 to 500μmol/L, with significant decrease in dry weight, root length, root surface area, root volume, lateral root, chlorophyl content, apoplast CO₂ concentration(Ci), photosynthetic rate (Pn) and transpiration rate at 500 μmol/LCu level, as compared with the control. In contrast, the growth of Elsholtzia argyi was inhibited severely even at low Cu level, and all the parameters of root morphology varied slightly with increasing external Cu level. Fv/Fm,Fo/Fm,F'v/F'm,Φ_PSâ…¡ and ETR significantly decreased whereas Fo increasedin E. argyi when grown at Cu supplying level >50 ^mol/L, the same results were found in E. splendens at 500|^mol/L Cu level. Copper content in shoot of Elsholtzia splendens was much higher than Elsholtzia argyi, which suggested that Elsholtzia splendens has better ability to transfer Cu from roots to shoots.2. The different responses of E. argyi and E. splendens to Pb toxicity in the presence or absence of EDTA addition were investigated. After 8 d's Pb treatment, root length, root surface area and root volume of E. splendens decreased much more than those of E. argyi, and reduced considerably with increasing Pb, while no marked change was noted for root average diameter. Compared to E. argyi, length of root with diameter (Z))<0.2 mm was significantly reduced for E. splendens as Pb increased. E. splendens roots with ï¿¡><0.1 mm had cross-sectional surface area at Pb>10 mg/L, while it occurred at Pb>25 mg/L for E. argyi. The DW of E. splendens decreased much more than that of E. orgy with increasing Pb levels. E. argyi exhibited much higher tolerance to Pb toxicity than E. splendens. Treatment with 100 mg/L Pb plus 50 mmol/L EDTA significantly decreased the length and surface area of fine roots with D<0.2 mm, increased the length and surface area of medium size roots with 0.2