MEASURING REGENERATION OF DISSOLVED PHOSPHORUS IN PLANKTONIC COMMUNITIES

We developed a technique to measure the release of dissolved phosphoru s from entire or size-fractionated plankton communities. The method in volves radiolabeling the plankton with phosphate and then competitivel y blocking the reassimilation of released radiolabel with (PO4)-P-31. The increase in dissolved radioactivity is then assayed. The initial r atio of P-31 to radioactivity and the increase in dissolved radioactiv ity are used to estimate the release of dissolved phosphorus. Total (u nfractionated) regeneration rates from two oligotrophic lakes had a ra nge of 15-205 ng P liter(-1) h(-1). Regeneration by the <40-mu m fract ion accounted for an average of 77% of the total. The results indicate that microorganisms (protists and bacteria) are the major regenerator s of dissolved phosphorus in the plankton of these lakes.