Anthony D. Curtis and Deborah A. Waller.
Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529 USA.
Previous studies indicated that high levels of dietary nitrogen decreased rates of nitrogen fixation in termites (Breznak, 1973). We tested the effects of dietary nitrogen on termite nitrogen fixation rates in both field and laboratory studies. Ten field colonies of Reticulitermes Holmgren were collected and assayed for nitrogenase activity by acetylene reduction in July 1993, October 1993, January 1994, and April 1994. The nitrogen content (TKN) of wood obtained from each colony was determined using a CHN analyzer. We examined wood near sites of feeding activity, and wood was cleaned of debris of termite origin. There was no correlation between termite nitrogen fixation rates and the amount of nitrogen in their food for any of the four collection periods (p=0.47). These data indicate that the nitrogen content of termite food in field colonies does not affect termite nitrogen fixation rates. In laboratory experiments, termite nitrogen fixation rates varied depending on the concentration and form of combined nitrogen in the diet. Rates decreased when termites were fed filter paper treated with 3% solutions of amino acids (p<0.01), or ammonium nitrate (p<0.01) compared to water treated controls. In contrast, the nitrogenase activity of termites fed filter paper treated with either a 1% or 3% solution of urea did not differ from controls (p=0.86). These results indicate that the quality and quantity of dietary nitrogen affect nitrogen fixation rates in termites. Therefore, the nitrogen contribution of termites to forests may depend on the nutritional quality of available foods.
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Breznak, J.A., W.J. Brill, J.W. Mertins and H.C. Coppel. 1973. Nitrogen fixation in termites. Nature 244: 577-580.