Total dissolved carbohydrates in an enclosure experiment with unialgal Skeletonema costatum culture

Abstract

In a southern Norwegian fjord (Rosfjord) during POSER a plastic enclosure (1 m 0, 20 m depth) was filled with filtered fjord water enriched with inorganic nutrients and inoculated with a monoculture of Skeletonema costaturn. The enclosure was exposed to fjord conditions from March 18 to April 5, 1979. Pre-filtration had removed ca. 80 % of the bacterial population in the fjord water. Following a short lag phase, bacteria grew exponentially. After consumption of nitrogen-containing organic substances, dissolved carbohydrates were the main energy source; however, bacterial numbers did not increase further, probably due to grazing by nanoflagellates. In spite of sub-optimal light and temperature conditions, S. costaturn reached cell densities as high as 35. 106 dm-3 at 3 m water depth, since competing algae and grazing zooplankton were missing in the enclosure. The diatoms grew exponentially, with a division rate of p = 0.6 d-' and reached the stationary phase after 16 d, when inorganic nutrients were exhausted. During growth of S. costatum relatively high amounts of carbohydrates were released. Maximum concentrations followed the exponential phase, but highest release rates per cell -2.0 pmoles glucose equivalents cell-' d-' -were reached immediately after inoculation. Measurements at 3 h intervals at the end of the experiment showed that concentrations and therefore release activities varied abruptly within a few hours. Main release occurred from noon to midnight. Not all dissolved carbohydrates were immediately taken up by heterotrophic organisms, part of them could not be utilized, others only after adaptation or succession of bacteria. During the experiment, the proportion of the labile fraction to the total dissolved carbohydrates varied greatly.

Carbon, nitrogen, and carbohydrate fluxes during the production of particulate and dissolved organic matter by marine phytoplankton

“…Others have obtained nearly identical results in large-volume coastal seawater enclosure experiments where the peak of the phytoplankton bloom (14 d) was associated with accumulation of DOC (130-250 p,M C; Nor-r-man et al 1995). Similar observations of maximal DOC accumulations have been made during stationary phase in phytoplankton cultures (Guillard and Wangersky 1958;Hellebust 1974) and the end of phytoplankton bloom development at sea (Eberlein et al 1985;Carlson et al 1994;Williams 1995). Freshly produced phytoplankton DOM may significantly influence the composition of DOM in the surface ocean.…”

“…Carbohydrates in the form of exopolymers are released in large amounts by growing phytoplankton in cultures ( Guillard and Wangersky 1958;Eberlein et al 1983) and in the sea (Ittekot et al 1981;Barlow 1980). Predominance of carbohydrates in phytoplankton exudates may be one reason why 25-50% of marine HMW DOC is composed of polysaccharides (Benner et al 1992).…”

Net accumulation and flux of dissolved organic carbon and dissolved organic nitrogen in marine plankton communities

“…The production of polysaccharides by phytoplankton has most often been associated with diatoms and nutrient deficiencies (Myklestad 1977;Ittekkot et al 1981;Eberlein et al 1983;Guerrini et al 1998;Fajon et al 1999). However, the production of polysaccharides was almost constant in all the bags (Fig.…”

Phytoplankton-bacteria interactions: an apparant paradox? Analysis of a model system with both competition and commensalism

“…Many studies attempting to evaluate bacterial consumption of algal EOC (extracellular organic carbon) in natural waters have been carried out (Derenbach & Williams 1974, Itturiaga & Hoppe 1977, Smith et al 1977, Wiebe & Smith 1977, Lancelot 1979, Larsson & Hagstrom 1979, Bell & Sakshaug 1980, Burney et al 1981, Chr6st 1981, Itturiaga 1981, Cole et al 1982, Wolter 1982, Riemann & Ssndergaard 1984. Such studies have also been carried out in enclosure experiments (Eberlein et al 1983) and in laboratory systems (Bell et al 1974, Nalewajko et al 1976, Bell 1983. When excreted compounds are of low mineral nutrient content, bacterial growth will require concomitant uptake of dissolved phosphate and/or nitrogen compounds for synthesis of bacterial biomass.…”