JPR Advance Access originally published online on June 2, 2009
Journal of Plankton Research 2009 31(8):899-907; doi:10.1093/plankt/fbp037
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Response of heterotrophic bacteria, autotrophic picoplankton and heterotrophic nanoflagellates to re-oligotrophication
,*1 Institute of Biochemistry and Biology, University of Potsdam, Am Neuen Palais 10, D-14469 Potsdam, Germany 2 Limnological Institute, University of Constance, D-78457 Konstanz, Germany
* CORRESPONDING AUTHOR: norbert.kamjunke{at}ufz.de
Received on December 8, 2008; revised on May 5, 2009; accepted on May 7, 2009
| Abstract |
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We investigated the response of the microbial components of the pelagic food web to re-oligotrophication of large, deep Lake Constance where total phosphorus concentrations during mixing decreased from a maximum of 2.81 µmol L–1 in 1979 via 1.87 µmol L–1 in 1987 to 0.26 µmol L–1 in 2007. Measurements of heterotrophic bacteria, autotrophic picoplankton (APP) and heterotrophic nanoflagellates (HNF) in 2006 and 2007 were compared to values from 1987 to 1997. We hypothesized that the biomass and seasonal variability of all groups will decrease under more oligotrophic conditions due to reduced resource availability, particularly for APP and HNF but less for the competitively stronger bacteria. Average bacterial biomass between spring and autumn was unrelated to phosphorus, whereas the ratio of bacterial biomass to chlorophyll a concentration increased with decreasing trophy due to declining chlorophyll concentrations. In contrast, a unimodal relationship was found between APP and phosphorus with low biomass at low and high phosphorus concentrations and maximum biomass in between. Average HNF biomass decreased strongly by a factor of 10–30 with decreasing trophy, and chlorophyll-specific HNF biomass was unimodally related to phosphorus. The relative seasonal biomass variability did not change for any group during re-oligotrophication. To conclude, HNF responded much more strongly and bacteria less so than chlorophyll concentrations to oligotrophication, whereas APP exhibited a more complex pattern.
Present Address: Helmholtz-Centre For Environmental Research Ufz, Brückstraße 3A, D-39114 Magdeburg, Germany