Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 2, 1999
Publication Date: N/A
Interpretive Summary: Aquatic weeds can quickly take over lakes, rivers, irrigation canals, farm ponds and other watery habitats. They crowd out desirable native vegetation, clogs irrigation systems, and make waterways unsuitable or unpleasant for boating, fishing, and swimming. This research revealed differences in the chemical makeup of several aquatic plants from Fall River, California. Specifically, carbon, nitrogen, and phenolic acids differed among the five species examined. Contrary to published hypothesis carbon and nitrogen content were not good predictors of phenolic acid content. Predicting phenolic acid content is useful because phenolic acids are believed to protect plants from attack by insects or diseases. The nutrient and phenolic acid content of a plant affect the plant's nutritional value to a potential biological control organism and may affect the agents vigor and ability to impact an aquatic weed. The ability to predict when nutrients are high or phenolic acid content is low will be useful in determining the best time to release potential biological control agents in different water bodies.
Technical Abstract: Phenolic acids in plants serve as defense against attack by herbivores and microbes. Understanding how plant nutrient content affects the level of phenolic acids would be useful in the timing of applications of biological control agents for aquatic weeds. To test published hypotheses, we compared seasonal changes in tissue C, tissue N, C:N ratio, and total phenolic acids for five species of submersed plants from Fall River, California. Mean tissue C differed among the five species and was between 35 and 40%, except for Ranunculus aquatilis, which had a mean tissue C content of 26%. Mean tissue N differed among the five species; Ranunculus aquatilis had the lowest mean value (2.71%) and Zannichellia palustris the highest (3.74%). Mean C:N ratio was between 9.7 and 12.7. Mean phenolic acid content for Myriophyllum sibiricum was greatest among the five species examined and, was nearly seven times that for the species with the lowest phenolic acid content, Elodea canadensis. Results from regression analysis indicated positive relationships between phenolic acid content and tissue C for only two species, Callitriche hermaphroditica and Ranunculus aquatilis. For regression equations relating phenolic acid content to tissue N, none of the slopes was statistically significant. For Elodea canadensis, the equation describing phenolic acid content as a function of the C:N ratio had a negative slope while, the equation for Callitriche hermaphroditica, had a significant positive slope.