Elemental Analyses of Marine Phytoplankton Purified by Cell Sorting

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Much can be learned of the nutritional status, relative growth rates, physiology and food web position of particular organisms from biochemical and stable isotope measurements. However, these measurements are almost always complicated in natural field samples by the presence of contaminating detritus and other organisms. Since direct biochemical measurements of the bulk phytoplankton (collected on filters) are often equivocal, researchers have employed statistical methods and incubation experiments for determining phytoplankton biomass and assimilation patterns. A powerful alternative to these indirect solutions to the problem is flow cytometric cell sorting. Flow cytometry, which allows us to recognize several classes of phytoplankton based on their autofluorescence and light scatter properties and to physically separate these particles form all others, will be used to obtain samples from a variety of oceanic regimes for measurements of C and N (and secondarily, of the natural abundances of C and N stable isotopes). Specifically,Dr. Olson will answer the following questions about the nature and extent of N limitation in the oceans: * Is there a difference between the C:N ratios of phytoplankton cells (and of specific groups within the phytoplankton) in coastal waters and those in the oligotrophic ocean? * Are there seasonal differences in C:N ratio of phytoplankton? * Are there changes in C:N of the phytoplankton with depth? * Are there diel changes in C:N ratios in the phytoplankton? * What are the characteristics of the "non-phytoplankton" under these sets of conditions? The results will shed light on the extent of N-limitation int he oceans and on the ecological roles of different groups of phytoplankton, and will help interpret observed patterns of isotope abundance in water column particle samples. It should also act as a springboard for a variety of other biochemical measurements of specific components of the plankton.