Competition between heterotrophic and autotrophic microplankton for dissolved nutrients [Rhodotorula rubra, Selenastrum capricornutum]

When a heterotrophic (Rhodotorula rubra) and a phototrophic (Selenastrum capricornutum) plankton were grown together in dilute phosphate (Pi) continuous cultures, coexistence occurred only when the heterotroph was growth-rate limited by organic carbon (C). Because of its higher affinity for Pi, and because C starvation does not affect the heterotrophic yeast's ability to transport Pi, the concentration of organic carbon indirectly controlled the biomass of the photograph. The results support a threshold model of microbial growth.