Nitrogen dynamics in the tropical savanna of Australia

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Termites are super-abundant soil animals and play an important role on the decomposition of dead plant material containing little nitrogen in tropical terrestrial ecosystems. Most dead plant material contains only 0.03-0.7% nitrogen and C/N ratio is 70-500, while termites contain about 19% nitrogen and their C/N ratio is 4-12. Therefore, termites must solve this C/N balance problem by either increasing nitrogen intake or selectively eliminating carbon. Tayasu et al (1994) showed that about 50% of body nitrogen of a lower termite, Neotermes koshunensis comes from the air through the activity of nitrogen-fixing bacteria in the gut.In this study we examined mainly how termites solve C/N balance problem with reference to their role in ecosystems. We measured methane production by termites as a process of carbon elimination, showing that the methane production was high in soil feeding termites. Termites harbor abundant bacteria in the hindgut. Therefore, its was suspected that termites utilized the hindgut bacteria as a nitrogen source. We examined the activities of lysozyme which decomposes the cellwall of bacteria in termite guts. The activity of lysozyme of a wood-feeder, Reticulitermes speratus, which was produced in salivary gland, was high in the foregut, and the activity of protenase was high in the midgut. It was highly probable that lysozyme secreted from salivary gland to foregut digests the symbiont bacteria transferred by trophallaxis in the mid gut. We suspected that major food of soil feeding termites, which occupy about 50% of termites at genus level, and showed the presence of lysozyme activity in the gut, although we could not show if symbiont bacteria are their major food or not. We showed the tendency of soil-feeding in termites using stable isotope. We extended our studies into the nitrogen economy at colony level in the savanna of Queensland of Australia.