MEPS 245:21-31 (2002)  -  doi:10.3354/meps245021

Biochemical partitioning of photosynthetically fixed carbon by benthic diatoms during short-term incubations at different irradiances

K. Wolfstein*, J. F. C. de Brouwer, L. J. Stal

Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands
*Present address: Institute for Inland Water Management and Waste Water Treatment (RIZA), PO Box 17, 8200 AA Lelystad, The Netherlands. Email:

ABSTRACT: The partitioning of photosynthetically fixed carbon (C) into different fractions of intracellular and extracellular C pools by an axenic culture of Cylindrotheca closterium (Ehrenberg) and a field sample of natural benthic diatoms was studied using short-term incubation with 14C at different irradiances. Hence, excretion was directly dependent on the level of irradiance. During the incubations, a comparable amount of about 70 and 75% of the fixed C, respectively, was excreted by the culture and the field sample. This excreted C was distinguished in 2 operational fractions of attached (closely bound to the cells) and colloidal (soluble) material. In the field sample, the percentage of excreted C decreased at irradiances higher than 300 µmol photons m-2 s-1, but it was constant for the culture over the whole range of different irradiances applied. The percentage of extracellular polymeric substances (EPS) in the attached and colloidal material, as obtained by ethanol precipitation, was constant over the range of the provided irradiances for both samples. Subsamples of natural benthic diatoms were treated with an antibiotic cocktail in order to exclude bacterial activity which resulted in unexpected higher values of incorporated C in the fractions of total C, intracellular C, colloidal C and EPS.

KEY WORDS: Cylindrotheca closterium · Extracellular polymeric substances · Microphytobenthos · P/E curves · Photosynthesis

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