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The accumulation of inorganic carbon from seawater by eukaryotic marine phytoplankton is limited by the diffusion of carbon dioxide (CO2) in water and the dehydration kinetics of bicarbonate to CO2 and by ribulose-1,5-bisphosphate carboxylase/oxygenase's (RubisCO) low affinity for its inorganic carbon substrate, CO2. Nearly all marine phytoplankton have adapted to these limitations and evolved inorganic carbon (or CO2) concentrating mechanisms (CCMs) to support photosynthetic carbon fixation at the concentrations of CO2 present in ocean surface waters (< 10-30 microM). The biophysics and biochemistry of CCMs vary within and among the three dominant groups of eukaryotic marine phytoplankton and may involve the activity of external or intracellular carbonic anhydrase, HCO3- transport, and perhaps a C4 carbon pump. In general, coccolithophores have low-efficiency CCMs, and diatoms and the haptophyte genus Phaeocystis have high-efficiency CCMs. Dinoflagellates appear to possess moderately efficient CCMs, which may be necessitated by the very low CO2 affinity of their form II RubisCO. The energetic and nutrient costs of CCMs may modulate how variable CO2 affects primary production, element composition, and species composition of phytoplankton in the ocean.

Phytoplankton is a nineteenth century ecological construct for a biologically diverse group of pelagic photoautotrophs that share common metabolic functions but not evolutionary histories. In contrast to terrestrial plants, a major schism occurred in the evolution of the eukaryotic phytoplankton that gave rise to two major plastid superfamilies. The green superfamily appropriated chlorophyll b, whereas the red superfamily uses chlorophyll c as an accessory photosynthetic pigment. Fossil evidence suggests that the green superfamily dominated Palaeozoic oceans. However, after the end-Permian extinction, members of the red superfamily rose to ecological prominence. The processes responsible for this shift are obscure. Here we present an analysis of major nutrients and trace elements in 15 species of marine phytoplankton from the two superfamilies. Our results indicate that there are systematic phylogenetic differences in the two plastid types where macronutrient (carbon:nitrogen:phosphorus) stoichiometries primarily reflect ancestral pre-symbiotic host cell phenotypes, but trace element composition reflects differences in the acquired plastids. The compositional differences between the two plastid superfamilies suggest that changes in ocean redox state strongly influenced the evolution and selection of eukaryotic phytoplankton since the Proterozoic era.

Metabolic responses to the subacute toxicities (non-growth-rate inhibiting) of Cd, Cu, and Zn were measured in the coastal marine diatom Thalassiosira weissflogii using calorespirometry. Respiratory heat production and oxygen consumption rates were measured in diatom cells grown with concentrations of Cd2+ (10-12 to 10-8 M), Cu2+ (10-13.8 to 10-9.8 M), and Zn2+ (10-10.9 to 10-6.9 M) that are typical of urban and suburban coastal waters. These trace metals did not significantly inhibit diatom growth rates in high-nutrient, high-light laboratory cultures except for the highest concentrations of Cd (Cd2+ = 10-8 M) and Zn (Zn2+ = 10-6.9 M). Respiratory heat rates in cells grown with elevated, but on-growth-rate-inhibiting free Cu2+ ion concentrations (10-11.8 to 10-9.8 M) were up to 40% higher and oxygen consumption rates were 50 to 75% lower than control ([Cu2+] = 10-10.8 M) cells indicating a subacute depression of respiratory efficiency in Cu-exposed cells. Exposure to elevated free Cd2+ concentrations (10-10 to 10-8 M) caused dramatic short-term (hours) increases (five- to eight-fold) in respiratory oxygen consumption rates, which returned to normal in acclimated cells, suggesting a transient disruption of metabolism upon Cd exposure. Zinc did not significantly affect either respiratory parameter up to a free Zn concentration of 10-7.9 M, above which diatom growth rate was significantly reduced. The subacute toxic effects of Cd and Cu were more pronounced in low Mn than in Mn-replete cells, consistent with proposed Mn- Cd, -Cu antagonisms in marine phytoplankton. The range of free Cu2+ ion concentrations in coastal waters is similar to that found to cause a decrease in respiratory efficiency in T. weissflogii, th... [ABSTRACT FROM AUTHOR]

Assesses the bioavailability of inorganic silver species and the importance of the low polarity AgCl complex to biological uptake. Determination of the octanol-water partition coefficient of silver over a range of chloride concentration representatives of fresh to brackish water; AgCl as the principal bioavailable species of inorganic silver in phytoplankton.