Comparative photoheterotrophy, chemoheterotrophy, and photolithotrophy in a eutrophic reservoir and an oligotrophic lake [Phytoplankton]

Autoradiography was used to determine the role in the uptake of NaH14CO 3and [3H]glucose of specific microorganisms of two sizes (0.45-10 μ m and 10-165 μ m) in a eutrophic reservoir and an oligotrophic lake. Ultraplankton (0.45-10 μ m) dominated plankton numbers and metabolic activity in both systems. An increase in photolithotrophy during the fall was due to an increase in the activity, numbers · ml-1, or both, of specific phytoplankters rather than an increase in the percentage of viable cells. Many of the most abundant species were not the most productive in terms of inorganic C fixation. Single species dominated total inorganic C fixation in both systems. Light-mediated uptake of [3H]glucose was extensive in Flathead Lake; light bottle uptake averaged 365% of dark bottle uptake. Autoradiographs indicated that bacteria were responsible for the observed light-mediated uptake of [3H] glucose in both lakes. Chemoheterotrophy dominated all Lake Texoma samples. Simultaneous in situ NaH14CO 3and [3H] glucose incubations in Lake Texoma revealed an ability of Oscillatoria agardhii (Gomont) to be mixotrophic as well as photoheterotrophic.