Does Algal–Bacterial Phosphorus Partitioning Vary Among Lakes? A Comparative Study of Orthophosphate Uptake and Alkaline Phosphatase Activity in Freshwater

In order to distinguish the activity of phytoplankton and bacterioplankton in 13 lakes of widely varying trophy, we size-fractionated orthophosphate uptake and alkaline phosphatase activity. In most lakes, orthophosphate uptake was consistently and overwhelmingly associated with the smallest particles. Based upon indicators of algal and bacterial presence in each size class, we inferred that the bacterioplankton are responsible for ≥95% of the orthophosphate uptake in situ, except in lakes that are not phosphorus-deficient. In contrast, a large portion of the alkaline phosphatase activity was free in solution (median 46%), and much of the remainder (median 44%) was apparently associated with algae.