Phagotrophy and NH4+ regeneration in a three-member microbial food loop
Goldman, JC.; Dennett, MR.
Journal of Plankton Research 145: 649-663
In a series of batch experiments we compared the efficiency of nitrogen regeneration of a two- and three-member microbial food loop consisting of a mixed bacterial assemblage, a small (3-5 .mu.m) heterotrophic flagellate (Paraphysomonas sp.), and a large (7-12 .mu.m) heterotrophic flagellate (Paraphysomonas imperforata). In the two-member system the nitrogen regeneration efficiency for NH4+ (Rn) was 41% and the gross growth efficiency (GGE) was 57% during active grazing by the small flagellate on bacteria. Regeneration of NH4+ continued during the stationary phase so that Rn was 75% after .apprx.6 days incubation. When the larger flagellate was introduced at the end of the exponential growth of the smaller grazer in the three-member system, initially there was rapid regrowth of bacteria, tying up .apprx.15% of the nitrogen originally in the bacteria. The larger flagellate grazed the smaller one with a GGE of 55%. Total nitrogen regeneration efficiency through exponential growth of the larger flagellate was 73%. Because microbial food loops in natural waters are far more complicated and with more grazing steps than portrayed in this study, we would expect the bulk of nutrients within these systems to be recycled with little transfer to higher trophic levels.