Use of carbon and nitrogen isotope ratios in termite research

In this paper, I review carbon and nitrogen isotopic (natural abundance levels) studies of termites. The carbon isotope ratio of CH₄ emitted from termites, together with the emission rates of CO₂, CH₄ and H₂, showed several trends corresponding to the kinds of symbiotic microbes and feeding habits. The fraction of methane oxidized in the nest structure was estimated by comparing carbon isotope ratio of CH₄ emitted from the nest with that produced by termites in the nest. Symbiotic nitrogen fixation in the gut of termites has been shown to have a significant contribution to the nitrogen economy in some wood-feeding termites. The carbon isotope ratio distinguishes between C4 from C3 plants, and the fractional contribution of grass in the diet can thereby be estimated. The carbon and nitrogen isotope ratios in termites are discernible among soil-feeders, fungus cultivators and wood-feeders. Wood/soil-interface feeders have intermediate values between wood- and soil-feeders, and thus carbon and nitrogen stable isotope ratios are assumed to characterize the degree of humification of the material consumed by termites. It is suggested that carbon and nitrogen isotope ratios are useful indicators of the functional position of termites in the decomposition process. A similar isotope pattern has been obtained in earthworms, suggesting that isotope signatures might be useful parameters in investigating detritivorous animals in general.