In addition to being an economically important pest, termites are also important ecologically to forest ecosystems. They are closely linked with biogeochemical (nutrient) cycling. The major biogeochemical cycles are: hydrologic, carbon, oxygen, nitrogen, sulfur, and phosphorus (Staley and Orians 1992). Components of each conceptually belong to "reservoir pools". Depending on the scale, reservoir pools may include all or part of the atmosphere, the ocean, the sediments, and living organisms. In general, flux between reservoirs is dominated by the biota and their activities. Elements are exchanged slowly between some reservoirs over a long period of geological time (Rodhe 1992).

Termites are important in the carbon cycle through their roles as consumers and detritivores (DeAngelis 1992). The termite gut is host to protozoan and bacterial symbionts that are able to digest wood cellulose and thus release the energy otherwise unavailable to the insects (Waller and La Fage 1987). Termite foraging and tunnelling redistributes soil and increases the surface area available to bacteria and fungi (Wood and Sands 1978). The breakdown of lignin and cellulose found in wood is primarily facilitated by the enzymatic secretions of fungi (Bold et al. 1980). Fungi are also able to liberate various elements such as nitrogen, phosphorus, potassium, sulfur, iron, calcium, magnesium, and zinc (Bold et al. 1980). The ability of termites to influence the physical structure and chemical nature of their environment impacts vegetation and other components of the ecosystem (Wood and Sands 1978). Their effect on the nitrogen cycle has traditionally been recognized as returning nutrients to the ecosystem. However, recent studies indicate that termites may play a larger role in the cycling of nitrogen than was once thought.

The atmosphere is composed of 78% nitrogen as N₂ gas. This represents a reservoir pool for nitrogen in terrestrial ecosystems. Biota cannot use this element until it is "fixed" into useable forms. Nitrogen fixation most commonly occurs in two ways: lightning accounts for the fixation of 10% of global available nitrogen and the other 90% of fixed nitrogen is generated from the action of microbes. Free living bacteria, cyanobacteria, and symbiotic bacteria in nodules in the low O₂ environment within heterocysts of leguminous plants are all involved in microbial nitrogen fixation (Jaffe 1992). However, there is another place where nitrogen fixation occurs.

The microbial gut flora of termites include nitrogen fixing bacteria (Benemann 1973, Breznak et al. 1973, French et al. 1976, Potrikus and Breznak 1977, Prestwich and Bentley 1981). The rate at which nitrogen is fixed varies among termite species (Prestwich et al. 1980, Breznak 1984, Bentley 1987, Waller et al. 1989) and within species as a function of food quality (Breznak et al. 1973), termite caste (Prestwich et al. 1980, Hewitt et al. 1987), and termite size (Waller et al. 1989). Intraspecific variation may also exist due to seasonal factors (Pandey et al. 1992, Waller et al. 1989). Newly fixed nitrogen is incorporated into termite tissue, excretion products, and secretion products (Bentley 1984).

Benemann, J. R. 1973. Nitrogen fixation in termites. Science 181: 164-165.

Bentley, B. L. 1984. Nitrogen fixation in termites: Fate of Newly fixed nitrogen. J. Insect Physiol. 30: 653-655.

Bentley, B. L. 1987. Nitrogen fixation by Nasutitermes and Velocitermes in Venezuela. In: Eder, J. and Remhold, H. (eds.), Chemistry and Biology of Social Insects. Verlag J. Peperny, Munich, p. 365.

Bold, H. C., C. J. Alexopoulos and T. Delevoryas. 1980. Morphology of Plants and Fungi. Harper and Row, New York. pp. 610-612.

Breznak, J. A. 1984. Biochemical aspects of symbiosis between termites and their intestinal microbiota. In: Anderson, J.M., Rayner, A.D.M., and D.W.H. Walton, (eds.) Invertebrate-Microbial Interactions. Cambridge Univ. Press, Cambridge, U.K. pp.173-203.

Breznak, J. A., W. J. Brill, J. W. Mertins and H. C. Coppel. 1973. Nitrogen fixation in termites. Nature 244: 577-580.

DeAngelis, D. L. 1992. Nutrient interactions of detritus and decomposers. In: M. B. Usher, M.L. Rosenzweig and Kitching, R.L. (eds.) Dynamics of Nutrient Cycling and Food Webs. Chapman and Hall, London. pp.123-141.

French, J. R. J., G. L. Turner and J. F. Bradbury. 1976. Nitrogen fixation by bacteria from the hindgut of termites. J. Gen. Microbiol 95: 202-206.

Hewitt, P. H., M. C. Van der Westhuizen, T. C. De K. Van der Linde and R. A. Adam. 1987. Acetylene reduction by the harvester termite Hodotermes mossambicus (Hagen). J. Entomol. Soc. S. Africa 50: 513-520.

Jaffe, D. A. 1992. The nitrogen cycle. In: S. S. Butcher, R.J. Charlson, Orians, G.H. and G.V. Wolfe (eds.) Global Biogeochemical Cycles. Academic Press Ltd. London. pp. 263-284.

Pandey, S., D.A. Waller and A.S. Gordon. 1992. Variation in acetylene-reduction (nitrogen-fixation) rates in Reticulitermes spp. (Isoptera: Rhinotermitidae). Virginia J. Sci. 43: 333-338.

Potrikus, C. J., and J. A. Breznak. 1977. Nitrogen-fixing Enterobacter agglomerans isolated from guts of wood-eating termites. Appl. Envir. Microbiol. 33: 392- 399.

Prestwich, G. D. and B. L. Bentley, 1981. Nitrogen fixation in intact colonies of the termite Nasutitermes corniger. Oecologia 49: 249-251.

Prestwich, G. D., B.L. Bentley and E. J. Carpenter. 1980. Nitrogen sources for neotropical nauste termites: Fixation and selective foraging. Oecologia 46: 397- 401.

Rodhe, H. 1992. Modeling biogeochemical cycles. In: S. S. Butcher, R.J. Charlson, Orians, G.H. and G.V. Wolfe (eds.) Global Biogeochemical Cycles. Academic Press Ltd. London. pp. 55-72.

Staley, J. T. and G. H. Orians. 1992. Evolution of the biosphere. In: Butcher, S.S., R.J. Charlson, Orians, G.H. and G.V. Wolfe (eds.) Global Biogeochemical Cycles. Academic Press Ltd. London. pp 21-54.

Waller, D. A. and J. P. La Fage. 1987. Nutritional ecology of termites. In: F. Slansky, Jr. and J. G. Rodriguez (eds.) The Nutritional Ecology of Insects, Mites, and Spiders. John Wiley and Sons, New York. pp. 487-532.

Waller, D. A., G. A. Breitenbeck and J. P. La Fage. 1989. Variation in acetylene reduction by Coptotermes formosanus (Isoptera: Rhinotermitidae) related to colony source and termite size. Sociobiology 16: 191-196.

Wood, T. G., and W. A. Sands. 1978. The role of termites in ecosystems. In: M. V. Brian (ed.) Production Ecology of Ants and Termites. Cambridge Univ. Press, U.K., pp. 245-292.

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