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Gewählte Master / Diploma Thesis:

Gorana Rampazzo Todorovic (2005): Influence of rhizosphere microbes on heavy metal uptake by Salix caprea and Thlaspi goesingense.
Master / Diploma Thesis, BOKU-Universität für Bodenkultur. UB BOKU obvsg

Data Source: ZID Abstracts
Human activity has caused an accumulation of heavy metals in soils. Because current physicochemical practices for decontamination of soils are mostly expensive and often have a negative impact on soil physical, chemical and biological properties, soil friendly and economic phytoremediation technologies are required. One of the very promising phytoremediation technologies is phytoextraction, which uses metal tolerant and metal accumulating plants that accumulate the target heavy metals in their shoots. Model plants for technology development are hyperaccumulating plants. Processes in the rhizosphere of these plants, especially the role of bacteria in heavy metal mobilization and plant uptake, are still largely unknown, but are considered to have a significant influence on the uptake of heavy metals. In this study, the influence of different bacterial strains on heavy metal mobilization and uptake by hyperaccumulating plants and by metal accumulating trees was investigated. The Ni hyperaccumulator Thlaspi goesingense grown on Ni rich serpentine soil was inoculated with three different bacterial strains which were previously isolated from the rhizosphere of T. goesingense as well as with soil solution from the rhizosphere of T. goesingense. Generally a decrease of shoot biomass of all inoculated treatments, compared to the sterile control was found. Inoculation had no significant effect on Ni concentration in shoots compared to the sterile control. A significant increase of labile Ni concentration in soil was found for some planted treatments compared to the non-planted control, which is in contrast to previous investigations. The results indicate that inoculation with single microbial strains may have less effect on heavy metal uptake than a combination of several strains. Further, it is assumed that bacterial strains did not have enough time to establish in soil. In a second experiment, a heavy metal polluted soil was inoculated with ten different bacterial strains isolated from Salix caprea rhizosphere obtained from an indigenous Zn/Cd contaminated site. Pots were planted with one year old S. caprea cuttings. The control pots were planted but not inoculated. Only one inoculated treatment had significant signs of necrosis compared to all other treatments. Significant increase of leaf dry weight was found for three inoculated treatments compared to the sterile control. For one treatment, a significant decrease of leaf dry weight was found. No significant change was found for Cd and Zn concentration in leaves in the inoculated treatments compared to control. For some inoculated treatments, a relative increase of total metal content for Cd and Zn compared to control was found. The largest relative increase of total metal content was 28 % for Cd and 27 % for Zn. A relative decrease of labile Cd and Zn concentration in rhizosphere compared to bulk soil was found for all inoculated treatments. The largest decrease of labile metal concentration in rhizosphere was 31 % for Cd and 17 % for Zn. The results of these experiments suggest that some bacterial strains may have more effect on heavy metal concentration in shoots, whereas others may have more influence on biomass production. Since both metal concentration in leaves and leaf biomass are key factors for successful phytoextraction, the target inoculant should have an influence on each of the two characteristics. Based on the results of metal accumulation presented here it seems that plant effects on the labile metal fraction in the rhizosphere of S. caprea and T.goesingense are more important than those caused by microbial inoculates.

Beurteilende(r): Wenzel Walter

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