Phagotrophy and NH4+ regeneration in a three-member microbial food loop |
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Authors: | Goldman Joel C; Dennett Mark R |
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Institution: | Woods Hole Oceanographic Institution Woods Hole, MA 02543, USA |
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Abstract: | In a series of batch experiments we compared the efficiencyof nitrogen regeneration of a two- and three-member microbialfood loop consisting of a mixed bacterial assemblage, a small(35 µm) heterotrophic flagellate (Paraphysomonassp.), and a large (712 µm) heterotrophic flagellate(Paraphysomonas imperforata). In the two-member system the nitrogenregeneration efficiency for NH4+ (Rn) was 41% and the grossgrowth efficiency (GGE) was 57% during active grazing by thesmall flagellate on bacteria. Regeneration of NH4+ continuedduring the stationary phase so that Rn was 75% after 6 daysincubation. When the larger flagellate was introduced at theend of exponential growth of the smaller grazer in the three-membersystem, initially there was rapid regrowth of bacteria, tyingup 15% of the nitrogen originally in the bacteria. The largerflagellate grazed the smaller one with a GGE of 55%. Total nitrogenregeneration efficiency through exponential growth of the largerflagellate was 73%. Because microbial food loops in naturalwaters are far more complicated and with more grazing stepsthan portrayed in this study, we would expect the bulk of nutrientswithin these systems to be recycled with little transfer tohigher trophic levels. |
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