Nitrate availability and calcite production inEmiliania huxleyiLohmann

Abstract

High-calcifying cells of Emiliania huxleyi were grown on a synthetic seawater medium and the effect of nitrate (NO3) concentration on growth, calcite accumulation, calcification rate and DIC (dissolved inorganic carbon) utilisation determined. The stoichiometry between NO3 utilisation and calcite production was 1:6.5 (mol/mol). Calcification and growth were tightly coupled: calcite production ceased when cultures entered the stationary phase due to NO; depletion, but by adding a pulse of NO; growth and calcification were restored. The initial C/N ratio in the medium was important in relation to calcification rate. At 20/~M NO3 the total DIC (2 mM) was rapidly depleted, the calcification rate subsequently declining, whereas at 5 and 10/~M NO3 ~ rates of calcification were constant at 20 g carbon celt ~x 1014.h ~ throughout culture growth, excess DIC being present relative to the available NO3. Calcite production per unit NO3 was similar for isolates of E. huxleyi from neritic, oligotrophic and nitrate-rich waters. In laboratory cultures, where the photon flux density is optimised for growth, the initial NO; concentration is a reliable indicator of final calcite yield.

A review of the coccolithophorid Emiliania huxleyi (Prymnesiophyceae), with particular reference to growth, coccolith formation, and calcification-photosynthesis interactions

“…They concluded that CO2 from intracellularly converted bicarbonate was the major carbon source in photosynthesis, and this was further supported by experiments in which these cells were grown in the virtual absence of external molecular CO2 (Dong et al , 1999Nimer et al 1994a). It was also claimed that E. huxleyi is able to completely exhaust the DIC from a seawater medium (Dong et al , 1999Merrett et al 1993;Nimer & Merrett 1995). This implies removal of all bicarbonate and carbonate ions together with an equivalent number of calcium ion charges.…”

INORGANIC CARBON TRANSPORT IN RELATION TO CULTURE AGE AND INORGANIC CARBON CONCENTRATION IN A HIGH‐CALCIFYING STRAIN OF EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE)1

“…Alkalinity was measured according to Parsons et al (1989). as described previously (Dong et al 1993).…”

“…Measurement of calrtfication rate. Calcification was measured as described previously (Nimer and Merrett 1993). Cultures harvested at the required growth stage were resuspended in fresh growth medium (but lacking DIC) and taken to the compensation point in a Clark-type oxygen electrode (Hansatech Ltd., Kings Lynn, Norfolk, U.K.) calibrated according to Delieu and Walker (1972).…”

“…T h e generation of CO, from HC0,during calcification may provide some advantages in terms of photon and nutrient costs of carbon fixation in calcifying cells compared to other phytoplankton with CO, concentrating mechanisms (Raven and Johnston 1991). In contrast to cells in the exponential phase, stationary-phase cells in highcalcifying cultures of E. huxleyi with low external dissolved inorganic carbon (DIC) (Dong et al 1993) express external carbonic anhydrase (CA,,,) (Nimer et al 1994b).…”

Bicarbonate addition promotes coral growth

“…Until recently, the general view has been that, at concentrations greater than 2 mM, DIC in seawater is in ample supply compared with other essential solutes such as nitrate and phosphate and trace elements such as iron, zinc, and silicon. There is, however, a growing awareness (Raven 1993) that the supply of DIC limits photosynthesis in planktonic algae, seagrasses (Beer and Rehnberg 1997), coccolithophores (Merrett et al 1993;Israel and Gonzales 1996), and macroalgae (Johnston et al 1992). Several authors (Muscatine et al 1989b;Weis et al 1989;Dubinsky et al 1990;Lesser et al 1994) have speculated on DIC limitation in coral.…”