by

Wood-feeding termites possess symbiotic bacteria that are capable of fixing atmospheric nitrogen to ammonia. This bacterial process is not only central to termite nutrition, but it also has tremendous ecological importance as fixed nitrogen is often a limiting nutrient in terrestrial ecosystems. However, nitrogen fixation is energetically costly, and we therefore hypothesized that a high nitrogen diet would reduce termite dependence on symbiotic nitrogen fixation. This was tested by rearing workers of the eastern subterranean termite (Reticulitermes flavipes) on three food substrates—pine wood, pine needles, and aspen leaves—that differed significantly in percent nitrogen (0.07, 0.36, and 0.93 % nitrogen, respectively). Termite and representative food samples were analyzed using an isotope ratio mass spectrometer. A mixed model equation was applied to determine the percent nitrogen derived from the atmosphere within each termite sample. Initial results indicated that nitrogen fixation rates are plastic within R. flavipes and they are negatively correlated with dietary nitrogen, as hypothesized. A follow-up study was conducted to investigate three assumptions associated with the initial experiment. The first assumption is that only nitrogen concentration, and not the nitroge