Monday, December 10, 2007
D0079

The effect of dietary nitrogen on symbiotic nitrogen fixation in the eastern subterranean termite (Reticulitermes flavipes)

Megan E. Meuti, meuti.1@osu.edu, Susan C. Jones, jones.1800@osu.edu, and Peter S. Curtis, curtis.7@osu.edu. The Ohio State University, Entomology, 1991 Kenny Rd, Columbus, OH

Termites possess symbiotic bacteria that fix atmospheric nitrogen to ammonia. This process is not only central to termite nutrition, but also is ecologically important as nitrogen is often a limiting nutrient in terrestrial ecosystems. Because nitrogen fixation is energetically costly, we hypothesized that high dietary nitrogen would reduce symbiotic nitrogen fixation. To test this, workers of the eastern subterranean termite (Reticulitermes flavipes) were fed on three substrates-- pinewood, pine needles, or aspen leaves-- that differed significantly in percent nitrogen (0.07, 0.36, and 0.93% N, respectively). Termite and representative food samples were analyzed with an isotope ratio mass spectrometer, and the percent of fixed nitrogen within each termite sample was determined. Results indicate that nitrogen fixation rates are negatively correlated with dietary nitrogen as hypothesized. Currently we are investigating two assumptions associated with the initial experiment. First, the initial assumption that only the nitrogen source and not the concentration affects nitrogen fixation will be addressed by feeding R. flavipes workers different concentrations of either urea or ammonium nitrate. Second, because the isotope discrimination factor occurring as a result of digestion (Ädig) is not known for R. flavipes, Ädig was estimated by assuming that nitrogen fixation on aspen leaves (highest %N) was zero. Our estimates of Ädig (4.1-6.9) were slightly higher than those reported for other termite species. To accurately calculate Ädig, nitrogen fixation will be inhibited by feeding workers antibiotics. These studies represent the first attempt to employ stable isotopes to study nitrogen fixation in R. flavipes and therefore significantly extend what is known about this process.


Species 1: Isoptera Rhinotermitidae Reticulitermes flavipes (eastern subterreanean termite)