Nature of dissolved P regenerated by plankton: implications for the ssPO4 radiobioassay and for the nature of dissolved P |
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| Authors: | William D Taylor |
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| Institution: | (1) Department of Biology, University of Waterloo, Waterloo, ON, N2L 3G1, Canada |
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| Abstract: | Techniques recently developed for measuring P regeneration, particulate P turnover, and PO4
3− concentration in lakewater assume that dissolved 32P (D32P) released by plankton is PO4
3−. To test this assumption, I obtained samples of D32P regenerated from whole plankton communities by labeling the communities with 32P-PO4
3− then blocking re-uptake and transformation of regenerated D32P with two competitive inhibitors, unlabeled 31P-PO4
3− and pyrophosphate. Under these conditions, regenerated D32P accumulated and could be examined by gel chromatography to discern how much of it was 32P-PO4
3− versus higher molecular weight P compounds. I estimated that most or all of the D32P released was 32P-PO4
3−. I also observed that the amount of DP observed on filtration of lakewater depended on the method employed to obtain the
filtrate. Therefore, I also separated particulate 32P from D32P with dialysis membrane (100,000 MW cutoff) without pressure. There was little DP larger than PO4
3− and no DP >5,000 MW in the dialysate, leading me to conclude that DP <100,000 MW was a minor component of both regenerated
and total P. I suggest that under P-limited conditions that most dissolved P observed in lakewater filtrates may be intact
viruses and cell constituents liberated in the filtration process. These results are mostly congruent with Lean’s (J Fish
Res Board Can 30:1525–1536, 1973) model of P-cycling in lake plankton, although the nature of “colloidal P” in Lean’s model should be further investigated. |
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