FIG. 7.

Seawater samples were taken on 30 June 1998 and assayed for P. minimum ELF-97 labeling (Initial sample, Day 0). Water was then sealed in triplicate clear polycarbonate bottles and incubated in situ with either nothing added (No Addition, Day 3) or inorganic P added (+P Addition, Day 3) to a final concentration of approximately 36 μM. After 3 days, cell numbers and ELF-97 labeling were assessed. There was a significant difference in the levels of ELF-97 labeling between the control and +P treatments (84.6 and 59.3%, respectively; P < 0.05). This indicates that the activity of ELF-97-labeled alkaline phosphatase, our marker for P stress, was repressed when cells from field populations were refed with phosphate.