| Guangxi is known as the Town of Nonferrous Metals, and it ranks first because of the size and intensity of manganese mining. The original ecological environment of manganese mines has been destroyed heavily, and a large area of soil has been contaminated through many years exploring. In mining area, plant growth has been limited for high concentraion of manganese,cadmium and other heavy metals, which hindered healthy developmeng of its ecological restoration. So, it has become an imortant issue to be solved that the contents of heavy metals in the soil of wasteland should be reduced. In recent years, phytoremediation technology has attracted more and more concern of governments, scientific community and business community for its potential efficiency, low cost and environmentally friendly characteristics. For this technology, fast-growing an adaptable hyperaccumulators are used to remove heavy metals from soil by extraction of the heavy metals to their aerial parts.It was found that Polygonum Pubescens Blume had the characteristics of manganese hyperaccumulator through field investigation of the manganese mine in Quanzhou, and its manganese tolerance and hyperaccumulation was verified by nutrient solution culture experiment. Besides, Mn enrichment mechanisms of Polygonum Pubescens Blume was discussed by means of studying its physiological response to stress of manganese and chemical speciation and distributioncharacteristics of manganese in it. Moreover, the plant was planted in Mn-contaminated soil to investigate its accumulation of Mn. Also, Polygonum Pubescens Blume was interplanted with economic crops in soil collected from wasteland of manganese mine to investigate their remediation effect to the soil. The following results were obtained from these studies.Polygonum Pubescens Blume has high tolerance to manganese, and it can hyperaccumulating Mn from its grow medium, which show that it is a Mn hyperaccumulator. Mn contents in its organs are leaf> stem> root. With the maximum Mn concentration in leaf reaching1.66×104mg/kg, the plant grew well on Mn mine wasteland of Guangxi with Mn concentration being as high as2.5×105mg/kg. Under hydroponic conditions, with the Mn concentration in the media increasing, the manganese concentration in the organs of Polygonum Pubescens Blume increased. When the Mn concentration in the solution was1000μmol/L, the Mn concentration in leaf reached more than10000mg/kg. When the Mn concentration in the solution was8000μmol/L, the Mn concentration in stem reached more than10000mg/kg. The results of dynamic absorption experiment showed that Polygonum Pubescens Blume has strong absorption of Mn. After Mn was absorbed to its roots, it could be transferred to and stored in the aerial parts, but this process needed a certain amount of time. At first (0-4h), Mn contents in roots was bigger that those in stems and leaves. At about32h, Mn content in the plants showed the characteristics:leaf>stem>root.The results of physiological and biochemical experiments showed that chlorophyll content, contents of cell membrane permeability and MDA in Polygonum Pubescens Blume leaves had no significant difference compared with the control when Mn treatment concentration was not more than5000μmol/L, which suggested that cell membrane was not significantly poisoned. When manganese concentrations was as high as8000μmol/L, contents of chlorophyll content decreased, cell membrane permeability and MDA increased significantly. Considering resistance to oxidative stress effects, the resluts of our experiments showed that POD and SOD enzyme activity increased along with increasing concentration of Mn, which suggested that the two enzymes had the effect of scavenging active oxygen radical. CAT activity did not changed significantly, indicating that CAT was not the key enzyme of removing H2O2under the stress of Mn.The results of extraction experiments by using different extractants showed that water-extractable Mn and NaCl-extractable Mn predominated in stems of Polygonum Pubescens Blume, and water-extractable Mn, NaCl-extractable Mn and HCl-extractable Mn predominated in its roots and leaves. With the Mn supply increasing, the percentage of Water-extractable Mn decreased and the percentage of HCl-extractable and NaCl-extractable Mn increased in the roots, and Water-extractable and HCl-extractable Mn increased in the leaves. Considering the subcellular level distribution of Mn, the results of our experiments showed more than90%of total Mn was bound to cell wall and soluble fraction in the plant. Leaf was the key organ of Polygonum Pubescens Blume in which the Mn content was the highest. Under the stress of different Mn treatment concentration, Mn content in cytoplasmic soluble substances (including vacuoles) were the highest with the distribution proportion of55.92%-63.09%, which followed by that in cell wall with the distribution proportion of31.01%-35.50%. So, the vacuole and cell wall was the main position where the majority of Mn stored. The results of experiments also confirmed that.The results of soil culture experiments proved again that Polygonum Pubescens Blume has strong tolerance and accumulation ability of Mn. The plants grew well in three kinds of soil. Their biomass had no significant differences, and all of their translation coefficients of Mn were greater than1. The results of Mn gradient experiments with the soil collected from the biological garden of Guangxi normal university showed that Mn contents in Polygonum Pubescens Blume increased with the increaseing concentration of Mn in soil, and all of the biological enrichment coefficients and the translation coefficients were greater than1. The Mn content in aerial parts of the plants were more than10000mg/kg when the Mn concentration in soil was1000mg/kg, which achieved the standard of Mn hyperaccumulator. Adding Ascorbic Acid could improve the tolerance of Polygonum Pubescens Blume that it was still alive in the soil with Mn concentration being5000mg·kg-1. Adding Ascorbic Acid of lower concentrations could increase the Mn translocation amount of the plant from the Mn-contaminated soil, but higher concentration showed restrictive effect.Polygonum Pubescens Blume and economic crops were interplanted in the soil which was collected from the wasteland of a Mn mine of Quanzhou. The results showed that Mn absorption capacity of Polygonum Pubescens Blume was inhibited when it was interplanted with soybean. The biomass of Polygonum Pubescens Blume increased,but its Mn accumulation did not significantly change. Both biomass and Mn accumulation of Polygonum Pubescens Blume increased when it was interplanted with corn, with its Mn uptake increased by208.4%. From above results, it was visible that interplanting Polygonum Pubescens Blume with corn was ideal for remediating Mn-contaminated soil. |
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