Intraspecific variation in the red alga Portieria hornemannii : monoterpene concentrations are not influenced by nitrogen or phosphorus enrichment

The red alga Portieria hornemannii (Lyngbye) Silva was selected to test the effects of enhanced nutrient availability on the production of carbon-based secondary metabolites, because of its notable site-to-site variation in monoterpene production. On Guam, the major secondary metabolite produced by this alga is ochtodene, a cyclic monoterpene. Quantitative high-performance liquid-chromatography analysis of the extracts of P. hornemannii collected from six sites on Guam showed that both ochtodene and triglyceride concentrations differed significantly among sites. Internal nitrogen and phosphorus content of the algae did not correlate with the observed variation in chemistry. Experimental enhancement of N-alone, P-alone or N + P in the field for 5 wk failed to induce a significant change in ochtodene concentrations in the alga, while triglyceride concentrations increased significantly in the N + P treatment. Ochtodene and triglyceride concentrations did not change among similar treatments in shaded (18 d) and unshaded (11 d) fertilization experiments conducted in the laboratory. Variation in ochtodene concentrations in P. hornemannii cannot be attributed to N and P availability; however, the decrease in ochtodene and triglyceride concentrations during the shaded laboratory experiment suggests that light may be a factor influencing monoterpene biosynthesis. The difference in ochtodene concentration between the initial and final sets of field controls collected for the unshaded laboratory experiment suggests that temporal variation might also contribute to differences observed among the algae at the different sites. Received 11 June 1996 / Accepted 20 July 1996