Influence of light and nitrogen on the phlorotannin content of the brown seaweeds Ascophyllum nodosum and Fucus vesciulosus

摘要

Phlorotannins, C-based defence compounds in brown seaweeds, show a high degree of spatial and temporal v~ ation within seaweed species. One important model explaining this variation is the Carbon Nutrient Balance Mol (CNBM), which states that the relative supply of carbon and limiting nutrients will determine the level of defer compounds in plants. Nitrogen is often considered to be the limiting nutrient for marine macroalgal growth and I CNBM thus predicts that when the carbon:nitrogen ratio is high, photosynthetically fixed carbon will be allocal to production of phlorotannins. In the present study, we evaluated the effects of light (i.e. carbon) and nitro~ on the phlorotannin content of two intertidal brown seaweeds, Ascophyllum nodosum and Fucus vesiculosus. T was done in an observational field study, as well as in a manipulative experiment where plants from habitats w different light regimes were subjected to different nitrogen and light treatments, and their phlorotannin cont was measured after 14 days. The results showed that there was a negative relationship between tissue nitro~ and phlorotannin content in natural populations of F. vesiculosus, but not in A. nodosum. In the short term, phlorotannin content in both algal species was not affected by changes in nitrogen availability. Exposure to sunli: had a positive effect on the phlorotannin content in natural populations of both algal species but, in the manipulat experiment, only F. vesiculosus showed a rapid response to changes in light intensities. Plants subjected to sunli: contained higher phlorotannin content than shaded plants. In conclusion, the results imply that nitrogen availabi] explains some of the natural variation in the phlorotannin content of F. vesiculosus, but the light environment I greater importance than nitrogen availability in predicting the phlorotannin content of each species.