Light and nutrient status of algal cells

Abstract

Chemostats were used to construct nutrient (vitamin B 12 ) and energy budgets for the flagellate Monochrysis {Pavlova lutheri (Droop) Green) under varying conditions of nutrient and light limitation and luxury, the aim being to describe light limitation and luxury in terms analogous to those of the Cell Quota nutrient model. Measurements were made of steady-state dilution rate, biomass, cell quota, cell chlorophyll a, cell energy content, dark respiration and photosynthetic efficiency, under low irradiance (<i3Wperm 2 ).Cell energy content was 0-54 joules per million cells and was not influenced by growth rate or nutrient/light status. Cell chlorophyll a was 25 % less in the nutrient-limited cultures and did not show a clear trend with growth rate except in cultures receiving less than 4-3 W per m 2 . The effective specific extinction coefficient was 0-12 cm 2 per fig chlorophyll. The photosynthesis/irradiance relation was linear. The mean slope ( = efficiency) in samples from the light-limited chemostats was 0225 and was independent of dilution rate. Samples from nutrient-limited chemostats showed a much lower slope, which decreased with decreasing dilution rate. These findings were confirmed by the chemostat kinetic data. Dark respiration varied with dilution rate in a hyperbolic manner and was greater in the nutrient-than the light-limited chemostat.Light level had no effect on the subsistence quota when the nutrient was limiting, whereas under light-limiting conditions the subsistence quotas were enlarged in inverse proportion to the incident irradiance, thus showing a threshold rather than multiplicative interaction between light and the nutrient.Energy absorption was very little reduced on nutrient limitation, the great reduction in overall efficiency being associated mainly with the reduction in photosynthetic efficiency.The reciprocal of photosynthetic efficiency was shown to be analogous to a standardized nutrient cell quota, and an analogous coefficient of luxury could be defined as the ratio of the light-limited to nutrient-limited photosynthetic efficiency at the same growth rate. Thus, light limitation and luxury could be described in terms compatible with the nutrient model without having to introduce new concepts, and a practical criterion between light-and nutrient-limitation could be provided.

Microphytobenthos community production at a near-shore coral reef:seasonal variation and response to ammonium recycled by holothurians

“…Accompanying the production increase, an accumulation of phaeopigments indicated an enhanced turnover of biomass (Uthicke & Klumpp 1997). The increase of cc in nitrogen-enriched treatments of the latter study may support the concept that a low photon yield efficiency is an indicator for nutrient limitation (Droop et al 1982, Mills & Wilkinson 1986). The low a-values encountered throughout our study, in conjunction with the result of the enhancement experiment, indicate that microphytobenthos productivity on Great Palm Island is limited by the availability of inorganic nitrogen.…”

“…We presented area-specific values for the photosynthetic efficiency (cc) since these directly express the quantum yield efficiency (Droop et al 1982, Mills & Wilkinson 1986) if suitable units are chosen, i.e. moles of carbon fixed per moles of quanta.…”

A dynamic regulatory model of phytoplanktonic acclimation to light, nutrients, and temperature

“…Some researchers advocate a multiplicative interaction among light and nutrient limitation (Droop 1983), whereas others require that growth rate be either light-limited or nutrient-limited (Rodhe 1978). Moreover, the models are valid only under the restrictive conditions of balanced growth, which is achieved when the specific rates of change of all measures of biomass are equal (Eppley 1980).…”

Vitamin B,2 binding by microalgal exocrines: dissociation constant of the vitamin-binder complex determined using an ultrafiltration technique

“…Equation (1) transforms to K, is thus also the half-saturation constant for B,, binding (equal to the concentration of free vitamin present when half of the binding sites are occupied). Values of B, , and K, were obtained by fitting the experimental data to this expression using the method of Droop et al (1982;Appendix 2). Some examples of these fits are given in Fig.…”