Some experiments on phosphate assimilation by coastal marine plankton

A study of phosphate assimilation by coastal marine plankton revealed that both phytoplankton and microheterotrophs incorporated radioactive phosphorus (Super(33) p). Size fractionation of the particulate matter (using 1 {mu}m pore diam Nuclepore membrane filters), antibiotic treatment (using garamycin), and independent estimates of photoautotrophic (Super(14) CO Sub(2) uptake) and heterotrophic (Super(3) H-glucose uptake) activities were employed to separate phyto and bacterioplankton phosphate uptake. Results indicated that phytoplankton Super(33) P-uptake was best estimated by the fraction of particulate matter retained on the 1 {mu}m membrane filters. Usually, < 10% of the phytoplankton (based on chlorophyll a measurements) passed the 1 {mu}m pore-diam filters, whereas {approx} 90% of the heterotrophic activity passed. At least 50% of the Super(33) P-uptake was associated with the < 1 {mu}m fraction. It may be possible to resolve the phytoplankton and bacterial contributions to Super(33) P-uptake by comparing the percent of total Super(33) P-uptake with the percent of total Super(3) H-glucose uptake associated with the > 1 {mu}m fraction.