The influence of Glyceria maxima and nitrate input on the composition and 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 dissimilatory nitrate-reducing bacterial community was investigated. Anoxic freshwater sediment was incubated in pots with or without G. maxima and with or without addition of nitrate. After incubation the sediments were sampled. Dilution series of these sediment samples were incubated in deep agar tubes and almost all colonies from the most diluted tubes were isolated and purified. When the nitrate concentration was low, 80% of the nitrate-reducing community in the rhizosphere of G. maxima consisted of NO2--accumulating or NH4+-producing Bacillus strains. In bulk sediment with low nitrate concentrations, denitrifying Pseudomonas and Acinetobacter strains were dominant. The difference in the composition: of the nitrate-reducing community between sediment with or without plants disappeared when nitrate was added. Denitrifying pseudomonads then made up 78-86% of the nitrate-reducing community. This shows that when the nitrate concentration was low, the presence of G. maxima greatly influenced the nitrate-reducing community. However, when nitrate was present and available, the composition and nitrate metabolism of the dominant nitrate-reducing community was probably not affected by G. maxima.