Studies on the Factors Affecting the Release of Organic Matter BySkeletonema Costatum(Greville) Cleve in Culture

Abstract

A few studies on the excretion of organic matter by marine phytoplankton in culture have been reported (Guillard & Wangersky, 1958; Wangersky & Guillard, 1960; Stewart, 1963; Hellebust, 1965). Eppley & Sloan (1965) reported extensive excretion in Skeletonema costatum (Greville) Cleve cultures as they approached senescence and emphasized that excretion is inversely proportional to the physiological activity of cells. Hellebust (1965) demonstrated the release of high amounts (up to 38% of the carbon assimilated) of organic matter by Sk. costatum cells exposed to low light intensities. It is apparent that more knowledge is needed in order to define the intra- and extracellular factors affecting the excretion.

The effect of light and temperature on DOC excretion by phytoplankton

“…Under a 15 : 9 (W D) photoperiod, excretion rates were reduced as compared to the other two light regimes. These results differ from those reported by Ignatiades and Fogg (1973), whose data on the marine diatom Skeletonema costatum show little increase in DOC excretion as irradiance increased from zero to saturating levels.…”

“…Unlike Ignatiades and Fogg (19'73), Verity ( 198 1) used axenic and preacclimated cultures. Little is known about the effects of extremely high irradiance levels, such as do cause photoinhibition, as well as of extremely low levels, where photosynthetic rates are also severely limited. Ignatiades and Fogg (1973) reported higher absolute DOC excretion at inhibitory irradiance levels than those found under lower light intensities. Belay and Fogg (1978), using a similar 14C procedure, found a correlation between increases in photoin hibition and rates of DOC excretion in the freshwater diatom Asterionella formosa but did not compare these rates with those occurring under lower irradiances.…”

Factors affecting phytoplankton extracellular release in the Southern Bight of the North Sea

“…In addition, for each phytoflagellate population, a specific inverse relation holds between PER and mineral nitrogen concentration. This means that when nutrients decrease during a bloom because of phytoplankton uptake, higher quantities of photoassimilated carbon are released into the surrounding medium in agreement with Fogg's hypothesis (Fogg et al, 1965) and other studies (Ignatiades and Fogg, 1973;Iturriaga and Hoppe, 1977;Sharp, 1977;Wolter, 1982). None of these authors, however, reported a continuous relationship, probably because of heterogeneity in phytoplanktonic species composition.…”

“…On the other hand, most culture work shows higher rates of extracellular release when phytoplankton growth is limited either by nutrient depletion or by too high or too low light intensities (Fogg et al, 1966;Fogg, 1971Fogg, , 1977Myklestadt and Haug, 1972;Ignatiades and Fogg, 1973;Sharp, 1977). Fogg et al (1965) suggested that photo-assimilated carbon is released into the surrounding medium instead of being used for growth when depletion of nutrients prevents protein synthesis.…”

Ecological role of exopolysaccharides of Bacillariophyta: A review

“…Приведенные результаты согласуются с аналогичными исследованиями морской диатомовой водоросли Chaetoceros affinis Lauder (Myklestad et al, 1989). Кроме того, увеличение экскрекции углерода с 2-4% до 14-65% экспоненциально растущими клетками культуры S. costatum на экспоненциальной фазе роста установлено при дефиците питательных веществ (Ignatiades, Fogg, 1973).…”