Fractionation of Cd and P by Marine Phytoplankton

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ABSTRACTOCE-0137592In this project, researchers at Rutgers University will continue their ongoing studies of the dependence of cadmium uptake by coastal marine phytoplankton on taxonomic affinity, growth rate, relative concentrations of other bioactive metals, and the ambient dissolved concentration of carbon dioxide in seawater. With this renewal funding, the focus will be on laboratory culture studies to complement field work carried out over the last four years. Anticipating that the implications of the study will be of general applicability, the investigators have designed the study to quantify fundamental dependencies for several classes of phytoplankton. Nevertheless, a strong impetus for the work is the desire to understand cadmium/phosphorous fractionation in Southern Ocean surface waters. The team hopes to develop ground rules for the robust estimation of phosphorous utilization in past Southern Ocean surface waters from the Cd/Ca ratio of fossil planktonic foraminifera. The three-year project will address two major questions: (1) Does uptake of Cd depend strongly on phytoplankton phylogeny, or are cell size, growth rate and availability of other metals more important? (2) Is increased Cd uptake with decreased pCO2 found in all major phytoplankton groups, or just diatoms, and is it caused by a physiological response to pCO2 or by pH-dependent changes in water chemistry? To answer these questions the research team will conduct two sets of experiments. First, they will determine Cd uptake in phytoplankton species from four major taxonomic groups, and test the dependence of Cd uptake on availability of other bioactive metals and on growth rate. Secondly, they will investigate the mechanism and ubiquity of Cd uptake control by ambient dissolved CO2 concentration by measuring the effect of varying CO2 on species across a wide phylogenetic spectrum of the phytoplankton. As part of the latter studies, they will conduct experiments to distinguish a physiological role for Cd in carbon acquisition from pH effects on availability of competing metals.