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Nitrogen dynamics in the tropical savanna of Australia

澳大利亚热带稀树草原的氮动态

基本信息

批准号：
10044205
负责人：
ABE Takuya
金额：
$ 4.35万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

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.

白蚁是数量极其丰富的土壤动物，在热带陆地生态系统中对分解含氮量很少的死亡植物物质发挥着重要作用。大多数死亡植物材料仅含有0.03-0.7%的氮，C/N比为70-500，而白蚁含有约19%的氮，其C/N比为4-12。因此，白蚁必须通过增加氮的摄入或选择性地消除碳来解决这种C/N平衡问题。Tayasu等（1994）指出，新白蚁体内约50%的氮是通过肠道固氮菌的活动从空气中获得的，本研究主要从白蚁在生态系统中的作用出发，探讨白蚁如何解决C/N平衡问题。我们测量了白蚁作为碳消除过程的甲烷生产，表明甲烷生产在土壤喂养白蚁中很高。白蚁的后肠里有大量的细菌。因此，怀疑白蚁利用后肠细菌作为氮源。本文研究了白蚁肠道中分解细菌细胞壁的溶菌酶的活性。黄胸散白蚁唾液腺分泌的溶菌酶在前肠中活性较高，蛋白酶在中肠中活性较高。由唾液腺分泌到前肠的溶菌酶极有可能阻断了中肠内通过互养转移的共生菌。我们怀疑土食白蚁的主要食物，其中占约50%的白蚁属水平，并显示溶菌酶活性的存在下，在肠道中，虽然我们不能表明，如果共生细菌是它们的主要食物或没有。利用稳定同位素示踪技术，揭示了白蚁食土的倾向。我们在澳大利亚昆士兰州的稀树草原上扩展了我们的研究到群体水平的氮经济。