Emiliania huxleyi (strain L) expressed an exceptional P assimilation capability. Under P limitation, the minimum cell P content was 2.6 fmol P ؒ cell Ϫ 1 , and cell N remained constant at all growth rates at 100 fmol N ؒ cell Ϫ 1 . Both, calcification of cells and the induction of the phosphate uptake system were inversely correlated with growth rate. The highest (cellular P based) maximum phosphate uptake rate ( V max P ) was 1400 times (i.e. 8.9 h Ϫ 1 ) higher than the actual uptake rate. The affinity of the P-uptake system (d V /d S ) was 19.8 L ؒ mol Ϫ 1 ؒ h Ϫ 1 at ϭ 0.14 d Ϫ 1 . This is the highest value ever reported for a phytoplankton species. V max and d V /d S for phosphate uptake were 48% and 15% lower in the dark than in the light at the lowest growth rates.The half-saturation constant for growth was 1.1 nM. The coefficient for luxury phosphate uptake ( Q maxt / Q min ) was 31. Under P limitation, E. huxleyi expressed two different types of alkaline phosphatase (APase) enzyme kinetics. One type was synthesized constitutively and possessed a V max and half-saturation constant of 43 fmol MFP ؒ cell Ϫ 1 ؒ h Ϫ 1 and 1.9 M, respectively. The other, inducible type of APase expressed its highest activity at the lowest growth rates, with a V max and half-saturation constant of 190 fmol MFP ؒ cell Ϫ 1 ؒ h Ϫ 1 and 12.2 M, respectively. Both APase systems were located in a lipid membrane close to the cell wall. Under N-limiting growth conditions, the minimum N quotum was 43 fmol N ؒ cell Ϫ 1 . The highest value for the cell N-specific maximum nitrate uptake rate ( V max N ) was 0.075 h Ϫ 1 ; for the affinity of nitrate uptake, 0.37 L ؒ mol Ϫ 1 ؒ h Ϫ 1 . The uptake rate of nitrate in the dark was 70% lower than in the light. N-limited cells were smaller than P-limited cells and contained 50% less organic and inorganic carbon. In comparison with other algae, E. huxleyi is a poor competitor for nitrate under N limitation. As a consequence of its high affinity for inorganic phosphate, and the presence of two different types of APase in terms of kinetics, E. huxleyi is expected to perform well in P-controlled ecosystems.

A variety of filtration and passive dialysis protocols were tested with seawater for determination of the dissolved concentrations of dimethylsulfoniopropionate (DMSPd), a compound originating in the cytosol of many marine phytoplankton. Commonly used sampling procedures, such as in‐line filtration, syringe pressure filtration, and gravity filtration of relatively large‐volume samples (5‐50 mL) through glass fiber filters, caused release of DMSPd from particulate material as evidenced by increasing DMSPd concentrations with volume filtered. Exposure of filters to air at the end of filtration caused particularly severe DMSPd release. Dialysis bags or Slide‐A‐Lyzer dialysis cassettes equilibrated with seawater DMSPd within 4 h, even in polar waters (−1.8 °C), and appeared to give accurate DMSPd concentrations in some circumstances. However, incubation of seawater in laboratory containers (e.g., glass jars) during dialysis sometimes caused artifactual release of DMSPd. We therefore adopted a small‐volume gravity drip filtration (SVDF) procedure, the essential elements of which were: (i) collection of 20 to 50 mL seawater directly from the primary sample container (e.g., Niskin bottle) into a dry, all‐plastic filtration tower; (ii) use of a 47‐mm‐diameter Whatman GF/F filter; (iii) rapid (< 3 min) filtration by gravity (hydrostatic) pressure; (iv) collection of only the first 3.5 mL filtrate for DMSPd analysis; and (v) never exposing the filtered plankton to air. The SVDF procedure appeared to yield the same low DMSPd concentrations as dialysis samplers incubated in the ocean water column. Using the SVDF procedure, DMSPd was found to be < 2.8 nM over a broad range of ocean water types and particulate DMSP concentrations. The maximum DMSPd concentration observed in our study (2.8 nM) was far lower than the reported worldwide average DMSPd concentration of 16.9 nM, raising the possibility that past data collections may have been influenced by filtration artifacts.

Dimethylsulfoniopropionate (DMSP) accounts for most of the organic sulfur fluxes from primary to secondary producers in marine microbial food webs. Incubations of natural communities and axenic cultures with radio-labeled DMSP showed that dominant phytoplankton groups of the ocean, the unicellular cyanobacteria Prochlorococcus and Synechococcus and diatoms, as well as heterotrophic bacteria take up and assimilate DMSP sulfur, thus diverting a proportion of plankton-produced organic sulfur from emission into the atmosphere.