bulbous rush colonizing acidic sediments.pdfVIP

Symposium no. 06 Paper no. 475 Presentation: oral 475-1 Microbial interactions in the rhizosphere of bulbous rush colonizing acidic sediments CHABBI Abad (1), KüSEL Kirsten (2) and TRINKWALTER Tanja (2) (1) Department of Soil Protection Recultivation, BTU-Cottbus, Faculty of Environmental Science, P.O. Box 10 13 44, D-03013 Cottbus, Germany (2) Lehrstuhl für ?kologische Mikrobiologie, BIT?K,Dr. Hans-Frisch Str.1-3, Bayreuth 95440, Germany Abstract Bulbous rush (Juncus bulbosus) is a pioneer species in highly acidic mining lakes of the Lusatian mining district (Eastern Germany). The objectives of this work were to enumerate the root colonizing microflora in comparison to the rhizosphere microflora, to investigate the effect of oxygen and pH on the utilization of organic exudates by the rhizobacteria and the ability of root colonizing microflora to reduce iron and sulfate. Rhizosphere sediment and plants collected from the littoral area were used for incubation studies. Most probable number estimates of aerobic and anaerobic root colonizing bacteria capable to consume root exudates were similar to those of the rhizosphere sediment; but numbers of aerobes were significantly higher than those of anaerobes. At pH 3, root exudates were primarily subject to aerobic oxidation to CO2 and not subject to fermentation. However, at pH 4.5, root exudates were also rapidly utilized under anoxic conditions. Roots of Juncus plants were enriched with Fe(II)- oxidizing and goethite-reducing microbes. Under anoxic conditions, goethite was reduced by the root colonizing microflora indicating an iron-cycle at the root surface. Sulfate was not utilized under acidic conditions by the root colonizing microflora. In all incubation studies, the pH increased during the microbial consumption of exudates substrates both under oxic and anoxic conditions. Thus, due to the microbial turnover of organic root exudates, pH and CO2 levels might be elevated at the root surface and favor Juncus plants t