9618112 Targett Brown algal polyphenolics are acetate-malonate derived phloroglucinol (1,3,5- trihydroxybenzene) polymers with putative biological activity (herbivore deterrents, digestion reducers, antibacterial agents) that attain substantial concentrations in many brown algal species, and hence, represent a significant investment of plant resources. Ecological theories, such as optimal defense, resource availability, and growth differentiation balance, have attempted to provide an inclusive theoretical framework that balances improvements in plant fitness resulting from secondary metabolite production with the metabolic costs of these compounds. However, experimental tests of these theories have yielded mixed results. Our understanding of factors that control plant production of secondary metabolites is limited because experiments to date have focused primarily on correlations between plant stresses and plant secondary metabolite concentrations, rather than rates of metabolite synthesis and turnover. Information regarding phlorotannin concentration levels as they correlate to various environmental factors has been useful in establishing general trends, but increasingly, observations of inter- and intraspecific variation in brown algal phlorotannin concentrations are falling outside of the current theoretical framework. To truly understand the observed patterns of plant phlorotannin concentrations, it is essential to understand the effect that specific environmental factors have on rates of phlorotannin production and turnover. The goals of this project are: 1. To establish an accurate understanding of brown algal phlorotannin synthesis, turnover, and exudation rates, 2. To establish the magnitude of variation in these rates as a result of changes in nutrient (nitrogen) concentration, irradiance bevels, and grazing intensity, 3. To use the data as a framework for the evaluation of the carbon-nutrient balance hypothesis (CNB) and the induction hypothesis ( IND) in marine systems, 4. To quantitatively evaluate the cost of phlorotannin synthesis and maintenance under varying nitrogen, irradiance and herbivory regimes. This research addresses several competing ideas that attempt to account for variation in concentrations of carbon-based secondary metabolites in plants. It does so with a direct experimental approach (lab and field) to measurement of rates of phlorotannin synthesis, turnover and fate in temperate and tropical brown algal species. Understanding these mechanisms is central to understanding issues of resource allocation and cost of allelochemical production.
