Visual Observations of Phosphorus Movement Between Algae, Bacteria, and Abiotic Particles in Lake Waters

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Abstract
The transfer of 33P-PO4 into plankton and the appearance of labeled colloidal material occurs within minutes in lake water. It is difficult to clearly separate the microscopic forms involved in phosphorus transfer by mechanical means since size ranges of algae, bacteria, detritus, and colloidal matter overlap. To circumvent this problem we used microautoradiography and scanning electron microscopy (SEM) to describe the sequence in which bacteria, algae, and suspended particles remove 33P-PO4 from solution and the physical appearance of excreted material suspected of containing labeled phosphorus.Bacteria initially showed much more dense labeling with 33P-PO4 but, since the algal biomass greatly exceeded the bacterial biomass, algal 33P-PO4 incorporation represented the most significant uptake pathway. After 2 h 33P accumulated in both the detrital aggregates which were harboring bacteria and the "capsular" material surrounding Anabaena. When these suspected extracellular release sites were examined by SEM, we observed fibrillar and amorphous particles of colloidal size (.05–0.5 μm). The possible ecological roles of these colloidal substances are discussed.

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