Enhanced phosphorus accumulation efficiency by the pelagic community at reduced phosphorus supply: A lake experiment from bacteria to metazoan zooplankton

Abstract

The effects of experimentally reduced total phosphorus concentrations (TP) from 2.4 to 0.6 µmol L −1 on plankton community in a shallow lake were evaluated from the proportion between dissolved reactive P (DRP), dissolved nonreactive P (DOP) and particulate organic P (POP), and the stoichiometry among particulate organic carbon (POC), nitrogen (PON), and POP. In both triple ratios, DRP:DOP:POP and POC:PON:POP, we used POP as a key component to indicate shifts between P fractions and between nutrients in particulate organic matter. The enhanced P accumulation by the planktonic assemblage by 14% at reduced P supply was achieved by two steps, in the first year mainly at the expense of DOP and in the second year by DRP. The evidence that this increase of %POP of TP reflects the adaptive P utilization of the organisms under low P supply was substantiated by significant relationships between P fractions and changes in the community. A higher %POP of TP was associated with higher specific alkaline phosphatase activity and with tighter coupling between producers and consumers respectively—that is, driven from both the nutrient‐producer and the producer‐consumer interface. A lowered %DOP of TP was significantly related to smaller overall loss rates for the carbon pool of bacteria and algae, whereas %DRP of TP was correlated to the decrease of the biomass of most organism groups. Stoichiometric shifts toward a P‐rich assemblage under low TP have been justified by compositional shifts from N‐rich cyanobacteria to P‐rich eukaryotic algae and bacteria. The shifts toward POP in both triple ratios strongly indicated that the plankton community acted as a sink for phosphorus under reduced total pool size.

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