Distribution of stable isotopes in the ecosystem

This paper gives a summary of distribution regularity of the ratio of carbon to nitrogen isotopes in the ecosystem, together with a few applied examples. The subject is discussed under the following items: expression of the ratio of carbon to nitrogen isotopes; sites for nitrogen and carbon isotope fractionation; isotopic compositions in plants and animals; origin of organic substances in the coastal sediments; analysis for habitual eating by the lake system; and estimation of the fixed amount of N in soybeans by the combination of tracer method using stable and low-level radioactive isotopes. The following three subjects to be further studied are mentioned: 1) study of the ratio of natural stable isotopes by combining tracer method using stable and low-level radioactive isotopes, 2) analysis for the regularity of in vivo isotope distribution, and 3) study of molecular isotope distribution. (Namekawa, K.)