Partenaires et organisations internationales
(Anglais)
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AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GR, HU, IE, IL, IT, LT, LU, NL, NO, PL, PT, RO, SE, SI, SK, TR, UK
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Résumé des résultats (Abstract)
(Anglais)
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Microorganisms living in the rhizosphere can affect trace element (TE) uptake by plants. However, due to the complexity and difficult accessibility of this narrow zone around plant roots and the large variety of microorganisms living in the rhizoshpere, it is difficult to identify such effects and to attribute them to particular strains. To overcome this hurdle, we developed an agar system which allows us to grow plants under sterile conditions and to inoculate their rhizosphere with a single, well-defined microbial strain. This agar system provides a fast and easy method for the screening of many microorganisms in a short time. In addition, it is easily possible to modify rhizosphere solution parameters and thus to collect experimental data efficiently under well-controlled conditions. We used this agar system to study the effect of several bacterial strains on TE uptake by sunflower and wheat. In a first screening we found that most bacterial strains tested actually reduced TE uptake by both plants instead of enhancing it. We suspected that this was due to adding the bacteria to the system after plant establishment. We therefore repeated the tests with the most promising bacterial strains, comparing inoculation after plant establishment with inoculation at the very beginning of plant establishment (by seed-dipping). None of the microorganisms had an effect of plant biomass. They also had little impact on plant TE uptake. Mostly, again, the application of bacteria tended to decrease shoot TE concentrations. In the case of sunflower roots, bacteria added by seed-dipping tended to increase plant TE contents, whereas microorganisms applied later by inoculation had the opposite effect. In general, bacterial inoculation after plant establishment exerted a stronger effect than addition of bacteria by seed-dipping. Roots showed a stronger response in TE concentrations to microbial inoculation than shoots. The results suggest that the bacterial enhancement of plant TE uptake from soil reported by various authors generally was not due to increased efficiency of TE uptake by the roots but to TE mobilization in soil, that is to enhanced transfer of soil-bound TE from sorbing soil surfaces to the roots. In order to test this, we will add TE-binding solids to the agar system in future experiments and study how bacteria affect TE mobilization. Several experimental setups will be run in parallel for different sorbent materials. The use of a DGT (diffusion in thin films) device and sampling in the agar rhizosphere will allow us to quantify microbial TE mobilization and to determine the effects of such mobilization on TE availability for uptake by plant roots.
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