A new era of isotope ecology: Nitrogen isotope ratio of amino acids as an approach for unraveling modern and ancient food web

Food web research is rapidly expanding through study of natural fractional abundance of 15N in individual amino acids. This paper overviews the principles of this isotope approach, and from my perspective, reanalyzes applications, and further extends the discussion. It applies kinetic isotope effects that enriches 15N in certain amino acids associated with the metabolic processes, which was clearly demonstrated by observations of both natural ecosystem and laboratory experiments. In trophic processes 'trophic amino acids' such as glutamic acid that significantly enrich 15N, whereas 'source amino acids' such as phenylalanine and methionine show little 15N enrichment. Through various applications conducted over the years, the principles of the method have shown to operate well and disentangle complex food webs and relevant problems. Applications include food chain length estimate, nitrogen resource assessment, tracking fish migration, and reconstruction of paleodiet. With this approach, considerations of a wide range of classical issues have been reinvigorated, while in the same time, new challenging frontiers are emerging.

Automated summary

Food web research is expanding rapidly with the study of natural fractional abundance of 15N in individual amino acids. This paper provides an overview of the principles of this isotope approach and reanalyzes applications, as well as extends the discussion. The method applies kinetic isotope effects to enrich 15N in specific amino acids associated with metabolic processes, which has been demonstrated through observations in natural ecosystems and laboratory experiments. The application of this approach has proven to be successful in unraveling complex food webs and addressing various issues, such as estimating food chain length, assessing nitrogen resources, tracking fish migration, and reconstructing paleodiet.