THE INFLUENCE OF GLYCERIA-MAXIMA AND NITRATE INPUT ON THE COMPOSITIONAND NITRATE METABOLISM OF THE DISSIMILATORY NITRATE-REDUCING BACTERIAL COMMUNITY

The influence of nitrate addition and the presence of Glyceria maxima (reed sweetgrass) on the composition and nitrate metabolism of the dis similatory nitrate-reducing bacterial community was investigated. Anox ic freshwater sediment was incubated in pots with or without G. maxima and with or without addition of nitrate. After incubation the sedimen ts were sampled. Dilution series of these sediment samples were incuba ted in deep agar tubes and almost all colonies from the most diluted t ubes were isolated and purified. When the nitrate concentration was lo w, 80% of the nitrate-reducing community in the rhizosphere of G. maxi ma consisted of NO2--accumulating or NH4+-producing Bacillus strains. In bulk sediment with low nitrate concentrations, denitrifying Pseudom onas and Acinetobacter strains were dominant. The difference in the co mposition: of the nitrate-reducing community between sediment with or without plants disappeared when nitrate was added. Denitrifying pseudo monads then made up 78-86% of the nitrate-reducing community. This sho ws that when the nitrate concentration was low, the presence of G. max ima greatly influenced the nitrate-reducing community. However, when n itrate was present and available, the composition and nitrate metaboli sm of the dominant nitrate-reducing community was probably not affecte d by G. maxima.