This project involves the use radioactive phosphorus (33P) as a tracer in chemostat experiments to study the relationship between phosphate concentrations and growth rate in monospecific cultures of marine phytoplankton. For literally decades that relationship has been assumed to be described by the Monod equation, but the inability of colorimetric methods to accurately measure growth-rate-limiting concentrations of phosphate has precluded a rigorous test of this hypothesis. Theoretical analysis indicates that divergence from the Monod equation may be associated with diffusion of the growth-rate-limiting substrate through the boundary layer around the cell. Because the cell quota of limiting nutrient is more variable for phosphorus than nitrogen, it can be shown that the impact of diffusion through the boundary layer on the shape of the growth rate curve is likely to be much greater for phosphorus than for nitrogen. The intellectual merit of the proposed work lies in the use of tracer amounts of 33P to accurately measure phosphate in the nanomolar concentration range and the use of chemostats to provide rigorous control of growth rates. The combination of these methodologies offers by far the best chance of defining the relationship between phosphate concentration and growth rate and hence at last provide a rigorous test of the Monod growth model.
The broader impacts of the proposed work include the fact that the research will be a collaborative effort between Louisiana State University (LSU) and the University of Hawaii (UH) and will provide support for a graduate student at each institution. Both LSU and UH are EPSCoR institutions. Dr. Laws has written a textbook titled Mathematical Methods for Oceanographers (John Wiley) and teaches a graduate course at LSU that makes use of that text. The course and text include material on modeling. The results of the proposed work will be integrated into Dr. Laws' course and into future editions of his book and will be submitted for publication in the scientific literature. The broadest impact of the proposed work, however, will be on our understanding of the relationship that controls phytoplankton growth rates in phosphorus-limited systems and the outcome of resource competition among algae. For literally decades that relationship has been assumed to be the Monod equation. This project will use existing the tools to determine whether it is or is not.
