UC Davis

This study compares soluble phenolics and lignin content in two wetland macrophytes with contrasting life strategies grown under a varying nutrient supply in the field and in a greenhouse experiment. The differences are explained in terms of the protein competition model (PCM) hypothesis relating changes in secondary metabolites to changing nutrient limitation. The two study species, Eleocharis cellulosa (EC) and Typha domingensis (TD), are both widespread in tropical and subtropical freshwater and brackish marshes of the New World, and are often found in P-limited rather than N-limited conditions. TD is a fast-growing competitor with large nutrient requirements. EC is a stress tolerator, quite well adapted to growth in nutrient-limiting environments. In both species, the concentration of phenolics was negatively correlated with increasing growth (due to increasing nutrient levels). This is in agreement with the PCM hypothesis, which predicts an increase in phenolic synthesis when protein synthesis (and consequently growth) is low due to limited resource availability. An interesting difference was found in the correlation between tissue nutrients and phenolics. TD from both the field and the greenhouse showed a negative correlation between tissue P and phenolics, while EC displayed a significant negative correlation between tissue N and phenolics. EC is adapted to low P, and increased tissue P content represents luxury consumption (uptake of P for storage) which is not reflected in increased growth and thus is not correlated with phenolics. These are the first steps in elucidating the relationship among nutrient availability, growth and phenolic content in two important primary producers of tropical and subtropical marshes.