Microbial Processes Associated with Roots of Bulbous Rush Coated with Iron Plaques

• Published in: Microbial ecology Vol. 46; no. 3; pp. 302 - 311
• Main Authors: K sel, K., Chabbi, A., Trinkwalter, T.
• Format: Journal Article
• Language: English
• Published: New York, NY Springer-Verlag New York Inc 01.11.2003; Springer; Springer Nature B.V
• Subjects: Aerobes; Aerobic bacteria; Anaerobes; Anaerobic conditions; Animal, plant and microbial ecology; Anoxia; Anoxic conditions; Anoxic sediments; Aquatic plants; Biological and medical sciences; Carbon dioxide; Carbon Dioxide - analysis; Coal; Coal mining; Enumeration; Exudates; Exudation; Fermentation; Freshwater; Fundamental and applied biological sciences. Psychology; Goethite; Hydrogen-Ion Concentration; Iron; Iron - metabolism; Juncus bulbosus; Magnoliopsida - growth & development; Magnoliopsida - microbiology; Microbial ecology; Microbial flora; Microbiota; Microflora of plants; Microorganisms; Mining; Oxidation; Oxidation-Reduction; Oxides; Oxidizing agents; pH effects; Plant growth; Plant roots; Plant Roots - microbiology; Plaques; Rhizoplane; Rhizosphere; Root exudates; Roots; Sediments; Soil ecology; Soil Microbiology; Sulfate reduction; Sulfates; Sulphate reduction; Various environments (extraatmospheric space, air, water); Europe; Germany; Germany, Sachsen, Dresden; Biotope; Monocotyledones; Oxygen; Exudate; Root; Growth; Iron; Freshwater environment; Plant; Juncaceae; Juncus; Angiospermae; Coal; Turnover; Lakes; pH; Spermatophyta; Pioneer species
• DOI: 10.1007/s00248-002-1054-8
• ISSN: 0095-3628

Bulbous rush (Juncus bulbosus) is a pioneer species in acidic, iron-rich, coal mining lakes in the eastern part of Germany. Juncus roots are coated with iron plaques, and it has been suggested that microbial processes under the iron plaques might be supportive for Juncus plant growth. The objectives of this work were to enumerate the microbes involved in the turnover of iron and organic root exudates in the rhizoplane, to investigate the effect of oxygen and pH on the utilization of these exudates by the rhizobacteria, and to study the ability of the root-colonizing microbiota to reduce sulfate. Enumeration studies done at pH 3 demonstrated that 106Fe(III) reducers and 107Fe(II) oxidizers g$(\text{fresh}\ {\rm wt}\ \text{root})^{-1}$were associated with Juncus roots. When roots were incubated in goethite-containing medium without and with supplemental glucose, Fe(II) was formed at rates approximating 1.1 mmol g$(\text{fresh}\ {\rm wt}\ \text{root})^{-1}\ {\rm d}^{-1}$and 3.6 mmol g$(\text{fresh}\ {\rm wt}\ \text{root})^{-1}\ {\rm d}^{-1}$under anoxic conditions, respectively. These results suggest that a rapid microbially mediated cycling of iron occurs in the rhizosphere of Juncus roots under changing redox conditions. Most-probable-number estimates of aerobes and anaerobes capable of consuming root exudates at pH 3 were similar in the rhizosphere sediment and in Juncus roots, but numbers of aerobes were significantly higher than those of anaerobes. At pH 3, supplemental organic exudates were primarily subject to aerobic oxidation to CO2and not subject to fermentation. However, at pH 4.5, root exudates were also rapidly utilized under anoxic conditions. Root-associated sulfate reduction was not observed at pH 3 to 4.5 but was observed at pH 4.9. The pH increased during all root-incubation studies both under oxic and anoxic conditions. Thus, as result of the microbial turnover of organic root exudates, pH and CO2levels might be elevated at the root surface and favor Juncus plants to colonize acidic habitats.