engleski

Spatial and temporal distribution of nitrifying potentials of biofilms on submerged macrophyte Ceratophyllum demersum

The bacteria in water medium live in two completely different ways. Water column is inhabited by bacteria which make the bacterioplankton, while by attaching to the surfaces which are in contact with water, they form sessile communities. During attachment the bacteria extract extracellular polysaccharides. The growth developed in this way is called the biofilm. The submerged macrophytes can contribute to the considerable increase in the surface the water is in contact with. Considering the fact that Kopački rit is a eutrophycated area limited with nitrogen it was decided to carry out a research which would make us familiar with the distribution of nitrifying potentials on the submerged macrophyte Ceratophyllum demersum which grows in the Čonakut Channel in separate beds. The plants were sampled from June till September 2003. Nitrifying potential (NP) of biofilms was established on the older and younger parts of a plant. It was measured as the ability of oxidation of ammonia and nitrites by the nitrifiers in biofilm. This ability is expressed on the unit of the surface area of submerged macrophyte, on which the biofilm had developed. The ability of oxidation was established by measuring the concentration of the developed nitrites and nitrates after the incubation of macrophyte samples in a synthetic medium, in which the only source of nitrogen was ammonium-sulphate. Statistical difference in NP between older and younger parts of a plant appeared in September (t=-3.12, tCRIT=2.23, α =0.05). At that time the growth of filamentous algae and/or cyanobacteria appeared on the older parts of the plants. Since they can also be used as a substratum, the increased NP can be interpreted by the increase in the surface available for the colonization by the nitrifying bacteria. Although the results do not differentiate the young parts of the plant from the old ones, considering their different physiological status, the considerable difference between them still exists because of the appearance of filamentous algae and/or cyanobacteria only on older parts of the macrophytes.

Biofilm; nitrification; submerged macrophytes; spatial and temporal variability

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