MEPS 201:129-136 (2000) - doi:10.3354/meps201129
Physiology of the mixotrophic dinoflagellate Fragilidium subglobosum. I. Effects of phagotrophy and irradiance on photosynthesis and carbon content
Alf Skovgaard1,*, Per J. Hansen1, Diane K. Stoecker2
ABSTRACT: Photosynthesis was measured for the mixotrophic dinoflagellate Fragilidium subglobosum grown with and without prey (Ceratium lineatum), at 5 different irradiances. Photosynthetic rates were measured in phototrophically and mixotrophically grown cultures by use of the single-cell 14C uptake technique. Photosynthetic rates were reduced by 48 to 69% and cellular chlorophyll a (chl a) content was reduced by 13 to 67% in food-replete mixotrophic cultures as compared with strictly phototrophic cultures grown at the same irradiances. Under the same conditions, chl a-normalized photosynthetic rates were thus 7 to 49% lower in mixotrophic cultures than in strictly phototrophic cultures. It is, therefore, suggested that either the photosynthetic apparatus becomes less efficient when the cells are phagotrophically active or the chl a-normalized photosynthesis is reduced because fed cells contain photosynthetically inactive chl a in their food vacuoles. When food is abundant, the greater part of the gross carbon uptake of F. subglobosum is acquired through phagotrophy even at irradiances saturating for photosynthesis.
KEY WORDS: Mixotrophy · Dinoflagellate · Photosynthesis · Single-cell 14C technique · Chlorophyll a · Ingestion · C content · N content · C budget
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