土壌中の窒素・炭素同位体組成 : 有機物の続成過程に関連して

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Distributions of nitrogen and carbon isotopes in terrestrial ecosystems are described based on available data and our recent findings for soil organic matters. Major processes regulating N-isotope and C-isotope ratios in biogenic substances are discussed. The biological di-nitrogen fixation and the precipitation are major sources which lower the δ^<15>N value for forested soil organic matters. Denitrification enhances δ^<15>N value for soil in cultivated fields. An addition of chemical fertilizer lowers ^<15>N content in soils. The permiation of soil water is an important factor controlling vertical profiles of δ^<15>N in soil systems. Among soil organic matters, non-hydrolizable fraction seems to give unique low δ^<15>N value, suggesting the utility of δ^<15>N analysis in studying the nature of the fractions. δ^<13>C of soil organic matter is significantly lower than that for marine sediments. δ^<13>C for soil humus varies with respect to chemical forms as well as an age of soil organic matters. The variation is large in paddy fields. It is, thus, probable that δ^<13>C is an useful parameter in studying the early epidiagenesis of soil organic matters. Based on the known δ^<15>N-δ^<13>C relationships, a two-source mixing model has been applied to assess sources of organic matters in coastal sediment.
1980-08-30