Comparative photoheterotrophy, chemoheterotrophy, and photolithotrophy in a eutrophic reservoir and an oligotrophic lake 1

Autoradiography was used to determine the role in the uptake of NaH super(14)CO sub(3) and [ super(3)H]glucose of specific microorganisms of two sizes (0.45-10 mu m and 10-165 mu m) in a eutrophic reservoir and an oligotrophic lake. Ultraplankton (0.45-10 mu 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 super(-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 [ super(3)H]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 [ super(3)H]glucose in both lakes. Chemoheterotrophy dominated all Lake Texoma samples. Simultaneous in situ NaH super(14)CO sub(3) and [ super(3)H]glucose incubations in Lake Texoma revealed an ability of Oscillatoria agardhii (Gomont) to be mixotrophic as well as photoheterotrophic.