Rates and Ratios of Nitrogen and Phosphorus Released by a Bacterivorous Flagellate

Abstract

Rates and elemental ratios of nutrient released by a bacterivorous flagellate (Spumella sp.) were examined during the exponential and stationary growth phases of the flagellate. Two types of an isolated bacterium were used as prey: one was phosphorus-rich (C: N: P molar ratio = 59: 13: 1) and the other was phosphoruspoor (C: N: P=79: 17: 1). Specific release rates by the flagellate of ammonium, dissolved inorganic and organic phosphorus (DIP and DOP) were much higher during the exponential growth phase than during the stationary one. Ammonium and DIP release rates in the experiment using the P-rich bacterium (Experiment 1) were not so remarkably different from those using the P-poor bacterium (Experiment 2) during both phases. However, DOP release rates were much higher in Experiment 1 than in Experiment 2 during both phases. Ratios of ammonium released to total dissolved phosphorus released were significantly lower in Experiment 1 than those in Experiment 2 during both phases. Further, these ratios were higher than bacterial N: P ratios in both experiments. N: P ratios of nutrients released by the flagellate could have been determined by bacterial N: P ratios, but the release appeared more efficient for nitrogen than for phosphorus. © 1994, The Japanese Society of Limnology. All rights reserved.