TY - JOUR

T1 - Physiology of the mixotrophic dinoflagellate Fragilidium subglobosum. II. Effects of time scale and prey concentration on photosynthetic performance

AU - Hansen, Per J.

AU - Skovgaard, Alf

AU - Glud, Ronnie N.

AU - Stoecker, Diane K.

PY - 2000/8/9

Y1 - 2000/8/9

N2 - Photosynthetic performance and cellular chlorophyll a (chl a) content were studied in the mixotrophic dinoflagellate Fragilidium subglobosum during transition from phototrophic to mixotrophic growth and back again. Experiments were conducted at an irradiance of 50 μE m-2 s-1 and, for mixotrophic growth, in the presence of Ceratium tripos or C. lineatum. After 4 to 8 d in mixotrophic culture, cells of F. subglobosum had reduced both their cellular chl a content to 47% and the photosynthetic performance to ~42% of that found in phototrophic cultures. Net production of chl a in phototrophic and mixotrophic F. subglobosum cells was the same, indicating that feeding in F. subglobosum does not repress chl a production in mixotrophic cells. Thus, the reduction in cellular chl a content observed in mixotrophic F. subglobosum cells was caused by an increase in growth rate due to feeding. In cultures close to steady state, the photosynthetic performance at low prey concentrations was similar to values obtained by monocultures of F. subglobosum. However, above a certain prey concentration, photosynthetic performance decreased exponentially with an increase in prey concentration. The application of the traditional 14C labeled HCO3 - technique to measure photosynthesis in mixotrophically grown cells underestimated rates by 5 to 12%, probably due to fixation of CO2 produced from respiration of ingested carbon. In phototrophic and mixotrophic F. subglobosum cells 46 and 28% of the assimilated carbon is used for respiration, respectively. This indicates that F. subglobosum needs more energy to synthesize, maintain and run the photosynthetic apparatus than the heterotrophic apparatus involved in prey capture, digestion and assimilation.

AB - Photosynthetic performance and cellular chlorophyll a (chl a) content were studied in the mixotrophic dinoflagellate Fragilidium subglobosum during transition from phototrophic to mixotrophic growth and back again. Experiments were conducted at an irradiance of 50 μE m-2 s-1 and, for mixotrophic growth, in the presence of Ceratium tripos or C. lineatum. After 4 to 8 d in mixotrophic culture, cells of F. subglobosum had reduced both their cellular chl a content to 47% and the photosynthetic performance to ~42% of that found in phototrophic cultures. Net production of chl a in phototrophic and mixotrophic F. subglobosum cells was the same, indicating that feeding in F. subglobosum does not repress chl a production in mixotrophic cells. Thus, the reduction in cellular chl a content observed in mixotrophic F. subglobosum cells was caused by an increase in growth rate due to feeding. In cultures close to steady state, the photosynthetic performance at low prey concentrations was similar to values obtained by monocultures of F. subglobosum. However, above a certain prey concentration, photosynthetic performance decreased exponentially with an increase in prey concentration. The application of the traditional 14C labeled HCO3 - technique to measure photosynthesis in mixotrophically grown cells underestimated rates by 5 to 12%, probably due to fixation of CO2 produced from respiration of ingested carbon. In phototrophic and mixotrophic F. subglobosum cells 46 and 28% of the assimilated carbon is used for respiration, respectively. This indicates that F. subglobosum needs more energy to synthesize, maintain and run the photosynthetic apparatus than the heterotrophic apparatus involved in prey capture, digestion and assimilation.

KW - Chlorophyll a

KW - Dinoflagellate

KW - Fragilidium subglobosum

KW - Growth

KW - Mixotrophy

KW - Primary production

UR - http://www.scopus.com/inward/record.url?scp=0034625843&partnerID=8YFLogxK

U2 - 10.3354/meps201137

DO - 10.3354/meps201137

M3 - Journal article

AN - SCOPUS:0034625843

VL - 201

SP - 137

EP - 146

JO - Marine Ecology - Progress Series

JF - Marine Ecology - Progress Series

SN - 0171-8630

ER -