Differential response of tellimagrandin II and total bioactive hydrolysable tannins in an aquatic angiosperm to changes in light and nitrogen

The submerged freshwater angiosperm Myriophyllum spicatum produces high amounts of polyphenols, especially gallotannins, with broad biological activity against insect herbivores, algae, cyanobacteria and heterotrophic bacteria. To test whether resource availability explains the intraspecific variability of these hydrolysable tannins, the impact of light and nitrogen on the production and release of total polyphenols and tellimagrandin II, the major allelochemical present in M. spicatum was investigated. Axenic cultures grown in a controlled environment allowed to exclude any effects of herbivores, epiphytes or pathogens on phenolic compounds. Light had a strong positive effect both on tissue-bound and exuded polyphenolic compounds. Nitrogen availability neither influenced the total content of tissue-bound polyphenols nor the exudation of phenolic compounds. In contrast, at low nitrogen and low light availability tissue concentrations of the major polyphenol tellimagrandin II increased. These findings are important considering the allelochemical activity of M. spicatum polyphenols, especially tellimagrandin II. The results are assessed in the context of the recent debate on the validity of the carbon-nutrient balance hypothesis and possible other models.