Heterotrophy by phytoplankton and bacteria in Lake Michigan

Summary

Through several different measurements, dark heterotrophic uptake of glucose, adenine, and an amino acid mixture was demonstrated for Lake Michigan phytoplankton. The uptake experiments were conducted in the dark using concentrations of organics which were similar to ambient levels. Although rates of heterotrophic uptake varied considerably across seasons and among different locations, large, chlorophyll-containing particles (phytoplankton), accounted for a significant portion of dark uptake of dissolved organic matter. In some cases, over 60% of the measured heterotrophic uptake was attributed to phytoplankton. Movement of radioactive organics into phytoplankton cells was confirmed by grain density and track autoradiography.