The medium Aquil and its variations have been successfully used for trace metal studies of marine phytoplankton (diatoms and dinoflagellates) over the past three years. Here, the recipes, the methods of preparation and the chemical composition of Aquil are presented in detail. To permit complete definition of chemical speciation of the various components as calculated from thermodynamic equilibria, trace element contamination is controlled and the formation of precipitates and adsorbates is avoided. It is established that Aquil is suitable for physiological experiments with a variety of marine phytoplankters representing all major phyla. Modifications of the basic recipe and design of chemically defined media in general are discussed.
Zinc-deficient cultures of Thalassiosira pseudonana exhibited reduced silicic acid uptake rates. Copper toxicity decreased the silicic acid uptake rate at any zinc concentration. This resulted in the uptake rate being a function of the ratio in the medium of the cupric ion activity to the zinc activity rather than of either metal activity separately. These results are consistent with a proposed mechanism for the interaction between silicic acid and cupric ion activity involving a zinc-dependent active site.
Iron availability may limit carbon and nitrogenjxation i n the oceans. The freshwater cjanobacterium, Anabaena, was used as a laboratory model for the biochemical and physiological efects of iron. Increased iron nutrition, i n the range of lop8 M to l o p 6 M resulted i n increases of approximately f o u r fold i n carbon and nitrogen fixation rates. Chlorophyll concentration increased, and the relative amount of i n vivofluorescence was reduced with more iron. Natural samples of Trichodesmium, collected off Barbados and incubated with increased iron for two days, showed similar effects. Trichodesmium responded to iron additions indicating that it m a j be Fe limited in its natural environment. These responses to iron are consistent with the biochemical roles of iron i n photosynthesis and nitrogen fixation. The results are discussed i n the geochemical context of the sporadic total iron input to tropical oceans and possible implications to spatial and temporal patterns of productizity.
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