The effect of Lobelia dortmanna L. on the structure and bacterial activity of the rhizosphere

We demonstrate the impact of Lobelia dortmanna on the abundance and morphological structure and function of the bacterial biocoenosis occurring in the rhizosphere sediments. The metabolic activity of microorganisms, the intensity of respiration, the efficiency of respiratory chain and membrane integrity was evaluated. The significant influence of L. dortmanna on microbiological processes in the sediments was confirmed. Clearly the high amount, biomass and metabolic and physiological activity of bacteria in the rhizosphere sediments confirmed the stimulating effect of isoetids on sediment bacteria. The rhizosphere is inhabited by microorganisms which are very active in physiological and metabolic terms. This phenomenon is called the rhizosphere effect. The amount of carbon dioxide released in particular sediment zones was predominantly determined by the number of metabolically active cells and not by the respiration rate per single cell. The high respiration rate of bacteria in the rhizosphere was predominantly determined by high DOC concentration, as evidenced by the correlations between the parameters. The development of positive redox potential in the rhizosphere sediments by L. dortmanna was of considerable importance for the intensity of respiratory processes, which confirms the relationship between redox potential and CO2 concentration in the sediments. The specific system of functional relationships occurring between the roots of L. dortmanna and microorganisms present in bottom sediments is one of the important mechanisms enabling the well-functioning of this macrophyte in the littoral zone of soft-water oligotrophic lakes.