Abstract
We review the biochemical and physiological bases of the use of carbon and nitrogen isotopic compositions as an approach for environmental and ecological studies. Biochemical processes commonly observed in the biosphere, including the decarboxylation and deamination of amino acids, are the key factors in this isotopic approach. The principles drawn from the isotopic distributions disentangle the complex dynamics of the biosphere and allow the interactions between the geosphere and biosphere to be analyzed in detail. We also summarize two recently examined topics with new datasets: the isotopic compositions of individual biosynthetic products (chlorophylls and amino acids) and those of animal organs for further pursuing the basis of the methodology. As a tool for investigating complex systems, compound-specific isotopic analysis compensates the intrinsic disadvantages of bulk isotopic signatures. Chlorophylls provide information about the particular processes of various photoautotrophs, whereas amino acids provide a precise measure of the trophic positions of heterotrophs. The isotopic distributions of carbon and nitrogen in a single organism as well as in the whole biosphere are strongly regulated, so that their major components such as amino acids are coordinated appropriately rather than controlled separately.
Highlights
The biological processes that significantly affect the Earth's surface environment generally lack rigorous formulations because they are intrinsically elastic
The carbon and nitrogen isotopic compositions of diverse types of organic matter were measured and discussed by the pioneers of isotope geochemistry (e.g., Rankama 1948; Wickman 1952; Craig 1953; Hoering 1955; Parwel et al 1957), the isotopic fractionation associated with various biochemical reactions was only determined precisely after some time (e.g., Park and Epstein 1960; DeNiro and Epstein 1977; Hoering and Ford 1960; Wada 1980)
Wada and Hattori (1978) derived a more rigorous formula based on Michaelis-Menten kinetics to explain the nitrogen isotopic fractionation that occurs during nitrate assimilation by the marine diatom Phaeodactylum tricornutum (Figure 2d): εp 1⁄4 ε0þ þ ε2XY –ε0–X
Summary
The biological processes that significantly affect the Earth's surface environment generally lack rigorous formulations because they are intrinsically elastic. Wada and Hattori (1978) derived a more rigorous formula based on Michaelis-Menten kinetics to explain the nitrogen isotopic fractionation that occurs during nitrate assimilation by the marine diatom Phaeodactylum tricornutum (Figure 2d): εp 1⁄4 ε0þ þ ε2XY –ε0–X
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