Competition for Ammonium between Plant-Roots and Nitrifying and Heterotrophic Bacteria and the Effects of Protozoan Grazing

The competition for limiting amounts of ammonium between the chemolithotrophic ammonium-oxidizing species Nitrosomonas europaea, the heterotrophic species Arthrobacter globiformis and roots of Plantago lanceolata (Ribwort plantain) was studied in a series of model systems of increasing complexity, i.e. energy-limited continuous cultures, non-water-saturated continuously percolated soil columns and pots with γ-sterilized soil planted with axetic P. lanceolata seedlings. The effects of bacterial grazing by the flagellate species Adriamonas peritocrescens on the competition for ammonium were also investigated in the three model systems.