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scaling of compartmental fluxes of phosphorus in freshwater algae

By Yuan Hua Wed and Robert Henry Peters


The time courses of uptake, distribution, and excretion of radioactive PO, were determined for 11 species of freshwater algae. Uptake of PO, by algae was rapid, reaching a steady-state asymptote within an hour and maintaining that maximum for at least 10 h. Uptake could be described as a biphasic exponential function. The rate constants for uptake decreased with cell volume raised to a power of--0.25, whereas the uptake rates per cell increased with cell size to a power of-0.75, suggesting that small cells were much more efficient at sequestering PO,. Excretion of PO, by algae was fast during the first lo-20 min; thereafter, there was a slower prolonged loss of PO, for the remaining period. A two-compartment model could be convincingly fitted directly to the excretion time-course data. Both rate constants and flux rates of PO, excretion and intercompartmental exchanges showed a similar size-dependency to those of PO, uptake. The net uptake of PO, by algae increased proportionately to cell volume raised to a normalized power of 0.75. The allometric compartment model yielded estimates for net PO, uptake rates one order of magnitude higher than those determined by means of the Michaelis-Menten model. Phosphate uptake is thought to be the principal pathway of P accumulation by algae (Lean 1973). Because PO, uptake is mediated by an algal enzyme system, the rate parameter

Year: 2013
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