アミノ酸の窒素同位体比を用いた生物の栄養段階の解析 : 陸上環境を含めた生物生態系の解明に向けて(<特集>有機化合物の安定同位体比を用いた有機地球化学的研究の発展とその応用(Part II))

概要

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Recent evidences have suggested that compound-specific stable isotope analysis (CSIA) of amino acids has been employed as a new powerful method with that enables the estimation of trophic level of organisms in not only aquatic but also terrestrial food webs. This CSIA approach is based on contrasting the ^<15>N-enrichment with each trophic level between two common amino acids: glutamic acid shows significant enrichment of +8.0‰ with each trophic level, whereas phenylalanine shows little enrichment of +0.4‰. These ^<15>N-enrichments are well consistent in both aquatic and terrestrial organisms. The trophic level of organisms can be estimated within a small error as 1σ=0.12 for aquatic and 0.17 for terrestrial food webs, employing the eq.: [Trophic level]=(δ^<15>N_<glutamic acid>-δ^<15>N_<phenylalanine>+β)/7.6+1, where β represents the isotopic difference between these two amino acids in primary producers (-3.4‰ for aquatic cyanobacteria and algae, +8.4‰ for terrestrial C3 higher plants, and -0.4‰ for terrestrial C4 higher plants). Here, we briefly review this new method (i.e. CSIA of amino acids) and its application to natural organisms in terrestrial environments.
2011-09-30