| As indispensable food for people' s life, vegetables also play important roles for the health of human beings. With the improvement of people' s living standard, the demands for "clean vegetable" or "unpolluted vegetable" become stronger and stronger. Suburbs are areas for the production of vegetables and the disposal of solid refuse by means of landfill as well. And with the pollution of industry exhaust gas, waste residue, waste water and the let of the epilogue of the cars, soils are polluted by the irrigation of waste water, the pesticide, the herbicide and chemical fertilizers. Especially lead pollution in vegetable farm soils is more serious. The accumulation of the heavy metal-Pb in the root, stem, leaf and fruits not only affect the plant growth and development, but also can come into food chains to endanger the health of human beings. Therefore more and more attentions are paid to the heavy metal-Pb pollution in the graden soils. In this study, three representation vegetables-Chinese cabbage(leaf vegetable), Celery(stem vegetable), Pepper (fruit vegetable) were selected. We examined Pb's adsorption and desorption characteristics, the transformations and the influence of pH for Pb' s desorption-Pb physical chemistry action in the soil with the addition of Pb in two garden soils by the room culture experiments. Also, by hydroponic culture we studied lead' s influence on growth and development of vegetable crops, including of the root morphology and the change of SOD, MDA, Pro under Pb' s stress in the plant. And the thresholds for phytotoxicity or soil toxicity of Pb were studied by soil culture experiments. The main results obtained were summarized as follows: 1.The Isothermal curves of Pb of the adsorption on two garden soils(Qingzi garden soil and Huangsong garden soil)could both be described by either Langmuir, Freundlich or Temkin equation(R>0.90)for each equation, and arrived highly significant. Adsorption maxima calculated from the Langmuir equation were 14285.7 mg/kg, 12500mg/kg soil for Pb. Adsorption Pb by two garden soils increased with increasing adsorption respectively. There were highly positive linear relationships between adsorption and desorption(r=0.891, 0.955), arrived highly significant level.2.The phytoavailability of added Pb (Pb(NO3)2) deceased progressively with the incubation time. After 12 weeks, their transformations in two garden soils reached dynamic equilibrium,and their phytoavailability no longer decreased. After the equilibrium, about 90% Pb could not be extracted by 1 mol/L NH4NO3 (pH7.0)3. Lower concentration Pb in the medium accelerated the root development of Chinese cabbage and Celery, increased the biomass of the shoot. But with the increasing of the treatment concentration, Pb toxicity to vegetable crop gradually showed, and resulted in the inhibition of roots development. Root tip became black, the number of lateral root and root hair decreased, radical length, the root surface area, root volume decreased, leafs became yellow and easily fell off. Also, the florescence of Pepper declayed. All organs' biomass (fresh weight) of three vegetables decreased. Pepper died when adding 3000mg/kg Pb in soils. The tolerance of three vegetables for Pb is Celery>Chinese cabbage>Pepper.4. The activities of dismutase(SOD) of three vegetables in roots first rose, then declined. While the accumulation of melondialodehyde(MDA) content was not significant when lower Pb concentration. With increasing Pb concentration, MDA content increased gradually, while Pro content persistent increased.5 .The tolerance mechanisms of Pb mainly show that Pb in roots cell combined with cell wall, reached over 90%. Also, HCl-extractable Pb and HAc-extractable Pb became the dominative forms, reached over 90%, so decreased the Pb direct toxicity to cell membrane, restricted Pb transformation from roots to shoots, and decreased the toxicity for other tissues. 6.With the increasing of Pb treatment concentration, Pb content of all organs in three vegetables gradually improved, highest in ro...
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