Studies of Inorganic Nutrient Limitation in Planktonic Bacteria

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The growth of planktonic bacteria is generally assumed to be limited by depletion of organic carbon substrate. In contrast to this assumption, experimental work with natural bacterioplankton populations in Colorado lakes over the past several years show that growth of bacteria in these lakes is frequently limited by phosphorus. This proposal outlines a plan for testing the hypothesis that phytoplankton possess greater phosphorus storage capacity than bacteria, which offsets the kinetic superiority of bacteria under some conditions. Experiments will document (1) the phosphorus inventory of bacteria under nutrient-sufficient and nutrient-deficient conditions, (2) the uptake rate of phosphorus through both inorganic and natural organic phosphorus fractions by bacteria and by co-occurring phytoplankton assemblages, and (3) the phosphorus usage of bacteria and phytoplankton components in mixed communities for which organic phosphorus is the only phosphorus source, or for which inorganic phosphorus is supplied in a pulse, as might occur through nutrient patchiness in nature. The combined outcome of these three sets of experiments will demonstrate the influence of phosphorus storage capacity on the outcome of phosphorus competition between bacteria and phytoplankton.