9321535 COLLIER Differences in nitrogen nutrition might affect the distribution of phyoplankters because each nitrogen source has different patterns of availability. Ammonium, which is the preferred nitrogen source of most phytoplankton, is often not available in sufficient quantities to support phytoplankton growth. Therefore urea and nitrate are important nitrogen sources for the phytoplankton. Because urea like ammonium is produced within the plankton, while nitrate is supplied from deeper water, the relative availability of the various nitrogen sources changes both in space and in time. Marine cyanobacteria currently in culture are able to grow with ammonium or nitrate as sole nitrogen source, but only about half of them are able to utilize urea. This suggest that urea may affect the growth rate and distribution of marine cyanobacteria. This project, will develop molecular probes to cyanobacterial ureases which will then be used in field studies to examine the relationships between cyanobacterial urease utilization and basic oceanographic parameter. Molecular probes will be used because it is unlikely that any other techniques can provide the sensitivity and resolution required to understand these relationships. ***
