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Soils polluted by heavy metals can be reclaimed using a number of expensive tactics that either remove the contaminants or stabilize them within the soil. The value of metal accumulating plants for environmental remediation has recently been appreciated and promising results have been obtained. This paper reports a study on the behavior of Brassica napus, Brassica juncea, Raphanus sativus and Brassica carinata grown on a substrate contaminated by several heavy metals caused by the use of contaminated irrigation water. Data on carbon dioxide assimilation, biomass growth and the bioconcentration and translocation factor of each metal in each species were measured. The polluted substrate caused only a small variation in photosynthesis, however transpiration was more affected by the experimental substrate and in all three species of the genus Brassica the presence of metals in the substrate resulted in higher transpiration levels.Two bioconcentration factors were calculated respectively for the roots (BCF) and the shoots (BCF); the BCF was >1 for all the species for Cd, Cu, Ni and Zn without significant differences among species. All the values of BCF were lower than 0.5; among the metals, all Brassica species demonstrated a similar performance for Cd and Zn, whereas for other elements the bioconcentration factor was very low.  相似文献   
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 We studied the long-term effects (12 years) of municipal refuse compost addition on the total organic carbon (TOC), the amount and activity of the microbial biomass (soil microbial biomass C, BC and metabolic quotient qCO2) and heavy metal bioavaiability in soils as compared to manuring with mineral fertilizers (NPK) and farmyard manure (FYM). In addition, we studied the relationships between among the available fraction [Diethylenetriaminopentacetic acid (DTPA) extractable] of heavy metals and their total content, TOC and BC. After 12 years of repeated treatments, the TOC and BC of control and mineral fertilized plots did not differ. Soils treated with FYM and composts showed a significant increase in TOC and BC in response to the increasing amounts of organic C added. Values of the BC/TOC ratio ranged from 1.4 to 2, without any significative differences among soil treatments. The qCO2 increased in the organic-amended soil and may have indicated microbial stress. The total amounts of metals in treated soils were lower than the levels permitted by the European Union in agricultural soils. DTPA-extractable metals increased in amended soils in response to organic C. A multiple regression analysis with stepwise selection of variables was carried out in order to discriminate between the influence exerted on DTPA-extractable metals by their total content, TOC and BC. Results showed that each metal behaved quite differently, suggesting that different mechanisms might be involved in metal bioavailability Received: 31 October 1997  相似文献   
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In this work we studied the influence of Pb, Zn, and Tl on microbial biomass survival and activity during a laboratory incubation of soil. In comparison to uncontaminated soil, the microbial biomass C decreased sharply in soil contaminated with Zn and Tl, whereas the addition of Pb did not have any significant inhibitory effect on the level of microbial biomass C. Zn displayed the greatest biocidal effect, confirmed by the measurement of the death rate quotient (q D). The microbial activity, measured as CO2 evolution, increased significantly in contaminated soils, emphasizing the need of living organisms to expend more energy to survive. The greater demand for energy by microorganisms in order to cope with the toxicity of pollutants was also confirmed by measurement of the metabolic quotient (q CO2). In order to determine whether soil microorganisms affect the bioavailability of these metals through their mobilization and release, we studied the relationships between available Pb, Zn, and Tl, and microbial biomass C. The water-soluble fraction of Tl, available Tl, and Zn, and microbial biomass C were related significantly, but not Pb.  相似文献   
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Soybean ( Glycine max L.) plants, cv Richland, were grown during 30 days in a nutrient solution. After this period the plants were treated with a 50 μM Cd(NO3)2 solution. Sap flow rate and stomatal conductance were monitored during 4 consecutive days; at the end of this period relative water content and stomatal width and length were determined on fully expanded leaves. On the second day from the Cd treatment sap, flow rate and stomatal conductance in the treated plants were reduced to 60% of the control plants. Stomatal conductance kept on decreasing up to the fourth day. Cadmium decreased the leaf relative water content and the reduction in the stomatal closure was supported by an increase in the L/W ratio of the stomata. Root water uptake should be the primary mechanism reduced by Cd stress in soybean, and this reduction is consistent with the decrease in transpiration rate and with the stomatal closure.  相似文献   
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