Estimating organic P utilization by freshwater plankton using [³²P]ATP

Abstract

We examined the use of [ 32 ]ATP for the determination of dissolved organic phosphorus (DOP) utilization by freshwater plankton. Uptake of 32 P from ATP was rapid; plankton exhibited a higher affinity for the 32 P from ATP than for the previously used DOP analogue, methylfluorescein phosphate (MFP). The results suggested that phosphomonoesterase (PMEase) activity measured with [ 32 P]ATP was greater than alkaline phosphatase (AP) activity determined with MFP Therefore, the PMEase-enzymes responsible for DOP hydrolysis in the P-limited system we examined may include both the frequently measured AP as well the recently described 5′-nudeotidase. Uptake of tracer amounts of P from ATP into different size classes of plankton demonstrated that the bacterial size fraction (0.2–1μm;)dominates uptake, but this domination diminishes when DOP concentrations are elevated. [ 32 ]ATP is an effective and convenient substrate for tracing DOP dynamics in a manner comparable to using 32 PO 43− to study PO 43− dynamics.