Uptake and Recycling of Soluble Reactive Phosphorus by Marine Microplankton

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Abstract
Simultaneous measurements of soluble reactive P (SRP) uptake and regeneration (using isotope-dilution methodology) by natural marine microplankton [microzooplankton, phytoplankton and bacteria] populations are described for coastal and oceanic waters. Seasonal fluctuations in SRP fluxes in Bedford Basin (Canada) were characterized by high uptake and low regeneration rates during spring and fall bloom periods and higher relative (compared with uptake) and absolute regeneration rates during summer. On an annual basis, SRP regeneration by microplankton could meet .apprx. 50% of the P requirements for planktonic production. In oceanic waters microplankton were also important in recycling SRP, providing > 60% of the P-requirements for growth in the Peruvian upwelling region and in the Eastern Tropical Pacific Ocean. At times, > 100% of uptake requirements may be supplied by microplankton in Arctic waters. Size-fractionation studies showed that SRP uptake and regeneration were generally partitioned by particle size with relatively greater regeneration rates associated with organisms > 1 .mu.m in size.