| People has been paying a great attention to the phytoremediation technology because of its green, cheap and potential economic benefits. The hyperaccumulator plant is the basis of phytoremediation technology for soil heavy metal pollution. The improvement of heavy metals accumulation by means of fertilization to enhence plant's biomass is one of the effective ways for repairing efficiency. Pier is japonica Thunb. was used as an aim plant in this work. The pot experiments were performed to investigate the effects of nitrogen fertilizer forms (NH4+-N and NO3--N) on growth, physiological characteristics and Pb accumulation characteristics of Picris japonica Thunb. under the Pb stress. The main research results are as follows:(1) Picris japonica Thunb. did not show obvious harmful symptoms under different concentrations of Pb stress. From the growth of Picris japonica Thunb., it could be found that,the plant height and root length increased firstly and declined with the increase of nitrogen fertilizer, when NH4+-N fertilizer was exerted,.The plant height and dry weight presented a same trend with NO3-N fertilizer. The results indicated that, under the Pb stress, a moderate nitrogen fertilizer could be beneficial for the growth of Picris japonica Thunb. On the contrary, the growth of Picris japonica Thunb. could be inhibited with an excessive nitrogen fertilizer.(2) Under different concentrations of Pb stress, the overall exchangeable Pb increased gradually with the increasing of NH4+-N fertilizer. The opposite trend appeared when NO3-N fertilizer was used. Follwing the change of, the carbonate combination Pb, Fe and Mn oxidation Pb, organic combination Pb and reside Pb all had no obvious changes regardless of the change of nitrogen fertilizer dosage and form.(3) In contrast to the ck (ckl and ck2), NH4+-N fertilizer could reduce soil pH under Pb stress, and the more nitrogen fertilizer, the higher the pH decreased. The most decrease value of pH was 1.82 unit. When NO3--N fertilizer was applied, the pH increased slightly comparing to the ck(ckl and ck2), but the change was not significant. With the same level of nitrogen fertilizer and the same concentration of Pb stress, The pH with NH4+-N fertilizer was obviously lower than that of NO3--N fertilizer. (4) In low concentration of Pb stress, the Pb content of Picris japonica Thunb. In different organs, such as root, stem and leaf presented ascendant trend as NH4+-N fertilizer was increased. However, the Pb content in root, stem and leaf of Picris japonica Thunb, was in high level firstly and then decreased, when NO3-N fertilizer was increased. Among them, the Pb content of the root and leaf was the highest when the dosage of NO3-N fertilizer was 100mg/kg. Under high concentration of Pb stress, two forms nitrogen fertilizer had no significant effect to the Pb content of Picris japonica Thunb.'s stem. As for the root and leaf, their Pb content was in high level and then went down along with the increase of nitrogen fertilizer. When the dosage of nitrogen fertilizer was 400mg/kg their Pb content descended lower than that of ck2.The Pb distribution in Picris japonica Thunb. was in the order of root>leaf>steam as NH4+-N fertilizer was used. The Pb content of Picris japonica Thunb.'s leaf was higher than that of NO3--N fertilizer.In contrast to the NO3--N fertilizer, the application of NH4+-N fertilizer was more beneficial for transferring Pbto leaf.(5) Under low concentration stress of Pb, the chlorophyll of Picris japonica Thunb. increased with NH4+-N fertilizer increasing. The chlorophyll of Picris japonica Thunb. did not present an obvious change trend when the usage of NO3+-N was 50mg/kg. However, when the NO3--N>50mg/kg, its chlorophyll content still showed ascendant trend. Under high concentration stress of Pb, the chlorophyll of Picris japonica Thunb. rose firstly, then decreased with the NH4+-N fertilizer increasing. The highest chlorophyll appeared at the dosage of NH4+-N fertilizer of 50mg/kg. The chlorophyll of Picris japonica Thunb. dropped firstly and then increased and decreased later as NO3-N fertilizer increasing. When the dosage of NO3--N fertilizer was 100mg/kg, the chlorophyll content was the highest.As different concentration stress of Pb,the activities of SOD,POD,CAT increased firstly, and then descended with ehancing NH4+-N fertilizer. Under high concentration stress of Pb,the activities of CAT were both higher than ckl and ck2 when NH4+-N fertilizer was applied or NO3--N fertilizer... |
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