| Pokeweed (Phytolacca americana L.) was a new Mn hyperaccumulator found in China, it not only can hyperaccumulate Mn and Cd in its shoot, but also has a lot of other excellent characteristics, such as broad ecological amplitude, growing fast, high biomass, widely distributes and so on. Pokeweed is a good model plant for studying the the mechanism of heavy metal tolerance and hyperaccumulation by plant, also it is an ideal candidate for phytoremediation.In this thesis,1276pokeweed’s leaves samples and corresponding soil samples for41sites in China and Tokyo of Japan were collected. The relationship between Mn, Cd, Cu, Pb and Zn concentrations of leaves and soil was respectively analyzed, these were significant positive correlations between soil and leaves, The Pearson correlation coefficient for Mn, Cd, Cu, Pb and Zn respectively was0.626(p<0.001),0.985(p<0.001),0.4030<0.01),0.9080<0.001) and0.890(p<0.001). To compare metal accumulation abilities of these populations, bioaccumulation factors (ratios between metal content in leaves and in soils, BAF for short) were calculated. There was a very large extent and variability of Mn and Cd accumulation in natural populations of pokeweed. Among the5metals, Mn had the largest average BAF and the largest variation range which suggested these were great differences in the ability of Mn accumulation in these populations. The SY population was especially noteworthy with the highest BAF of18.6.Following the field survey, greenhouse experiments were carried out to compare the Mn and Cd tolerance and accumulation abilities of several pokeweed populations. The root elongation, biomass and content of chlorophyll of pokeweed seedlings from different population were analyzed under various Mn and Cd treatments, which suggested that the Mn and Cd tolerance and accumulation abilities of different populations were on an equal level, and the coefficient of variation on tolerant indices and metal accumulation between populations was less than20%. The seeds of SY populations which had a noteworthy performance in field survey were also collected and the characteristics in Mn tolerance and accumulation between SY and JS population were compared using solution culture. The results showed that these two populations possessed the similar ability of Mn accumulation. These above results suggested that the abilities of tolerance and accumulating Mn and Cd may be constitutive characteristics of pokeweed. In addition, our study also showed that when pokeweed seedlings was exposed in nutrient solution containing Mn with different pH values, the Mn concentration of shoot was similar, but the Mn concentration of root was raised with the pH increase, which indicated that the pH of growth medium played an important role in the Mn accumulating in the root of pokeweed.In the field survey, we found there were a lot of pokeweed plants growing well on the copper mining area and nearby. Hence the Cu tolerance and accumulation by pokeweed was studied comparing with Cd, the root elongation was severely inhibited when pokeweed was exposed to10μmol L-1Cu and completely stop root elongation by15μmol L"1Cu; however only up to200μmol L"1Cd could stop the elongation of pokeweed’s root. The content of leaf chlorophyll was descended with increasing concentration of applied Cu, and initial fluorescence (Fo), Variable fluorescence (Fv) and maximum fluorescence (Fm) of chlorophyll respectively showed a increasing, decreasing, and decreasing trend. But Cd treatment had little effect on these indexes. The dynamic accumulation of Cu and Cd in pokeweed plant using a short-time (48h) and a long-term (20d) exposure experiment also was compared, which show that most of the Cu was distributed in root, and the accumulating process mainly occurred in the early stages of treatment(0-4h for48h exposure and0-4d for the20d exposure). Although Cd concentration in root was highest among these organs, the accumulating Cd in organs of pokeweed was continuous, moreover, the transfer coefficient (the ratio of Cd in leaves to root) of Cd increased with the time. Further study about Cu and Cd distribution in different tissues/parts of pokeweed showed that Cu concentration inthe edge part of mature leaves was higher than the centre part and vein of mature leaves. In the root, the Cu in lateral root was as high as1567mg kg-1, but Cu in fleshy taproot and tender leaves was only69mg kg-1and82mg kg-1. Cd distribution in different tissues/parts of pokeweed showed a similar pattern, but the ratio of metal content in lateral root to the taproot for Cd (5.8) was much lower than the ratio for Cu (22.8). The subcellular distribution of Cu and Cd in the organs of pokeweed indicated that most of both metals were predominantly localized in the vacuoles.Many soils needed remediation are always contaminated by several kinds of metals. In order to remediate the multi-metal including Cu contaminated soils using pokeweed, several experiments including hydroponic and pot experiments were conducted to study the effects of applying EDDS on the growth and metal uptake of pokeweed. In the pot experiments, the biomass of pokeweed was about half of corn when they grew in same Cu contaminated soil, and the Cu concentration in shoot of pokeweed was about4times than that in corn, so pokeweed had a higher Cu extraction efficiency. When EDDS was applied at ambient temperature and followed by irrigation with hot water2d later, The Cu concentration of pokeweed’s shoot was3times more than that in corn, with a maximum value of241mg kg-1, which indicated that pokeweed had a great potentiality in the phytoremediation of heavy metal contaminated soil. In hydroponic experiment, the addition of5μmol L-1EDDS into treatment nutrient solution which contained10μmol L-1Cu could significantly alleviated the toxicity of Cu to the pokeweed, and reduced the Cu concentration of pokeweed’s shoot, When the dosage of EDDS addition increased to20μmol L-1, the toxicity of Cu to pokeweed was completely eliminated, simultaneously the Cu and Fe concentrations of root was also reduced. In the field experiments, EDDS application improved the copper content of corn, which was about1.8-6.1times than the control. Appropriate close planting of corn could improve the total Cu extract for unit area. In order to evaluate the potential environmental risk after EDDS application in field, the dynamic change of total and extractable metals, soil dissolved organic carbon (DOC) along the0-60cm soil profile was detected, which showed that the dissolved metals resulting from the application of3mmol kg-1EDDS to the Cu contaminated soil could be limited to the top30cm soil profile, the concentration of dissolved metals and EDDS in soil profile decreased with the time and the depth of soil. The concentration of dissolved metals and soil DOC almost returned to the control levels22days after EDDS application, which suggested the applied EDDS was almost fully degraded. In the whole period of experiment, no metal leaching down was detected resulting from the application of EDDS. |
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