Amino acid nitrogen and carbon isotope data: Potential and implications for ecological studies

Abstract

Explaining food web dynamics, stability, and functioning depend substantially on understanding of feeding relations within a community. Bulk stable isotope ratios (SIRs) in natural abundance are well‐established tools to express direct and indirect feeding relations as continuous variables across time and space. Along with bulk SIRs, the SIRs of individual amino acids (AAs) are now emerging as a promising and complementary method to characterize the flow and transformation of resources across a diversity of organisms, from microbial domains to macroscopic consumers. This significant AA‐SIR capacity is based on empirical evidence that a consumer's SIR, specific to an individual AA, reflects its diet SIR coupled with a certain degree of isotopic differences between the consumer and its diet. However, many empirical ecologists are still unfamiliar with the scope of applicability and the interpretative power of AA‐SIR. To fill these knowledge gaps, we here describe a comprehensive approach to both carbon and nitrogen AA‐SIR assessment focusing on two key topics: pattern in AA‐isotope composition across spatial and temporal scales, and a certain variability of AA‐specific isotope differences between the diet and the consumer. On this basis we review the versatile applicability of AA‐SIR to improve our understanding of physiological processes as well as food web functioning, allowing us to reconstruct dominant basal dietary sources and trace their trophic transfers at the specimen and community levels. Given the insightful and opportunities of AA‐SIR, we suggest future applications for the dual use of carbon and nitrogen AA‐SIR to study more realistic food web structures and robust consumer niches, which are often very difficult to explain in nature.

Application of a porous graphitic carbon column to carbon and nitrogen isotope analysis of underivatized individual amino acids using high‐performance liquid chromatography coupled with elemental analyzer/isotope ratio mass spectrometry

“…The AAs in organisms is independent of that in δ 15 N values. 3 Our determined δ 13 C and δ 15 N values of AAs in blue mackerel show a similar pattern to those in other marine organisms. Gly shows the highest δ 13 C values.…”

“…δ 13 C values varied from −20‰ to −5‰, whereas δ 15 N values had a larger variation from −20‰ to +18‰. δ 13 C and δ 15 N values of AAs do not show a significant correlation (R 2 = 0.370), suggesting that the change in δ 13 C values of AAs in organisms is independent of that in δ 15 N values 3 . Our determined δ 13 C and δ 15 N values of AAs in blue mackerel show a similar pattern to those in other marine organisms.…”

“…Compound‐specific stable carbon and nitrogen isotope (δ 13 C and δ 15 N) analyses of amino acids (AAs) have been used in a wide range of physiological, ecological, geochemical, cosmochemical, and archaeological studies as a complementary and improved method of conventional isotope analyses of bulk organic matter. Especially, δ 13 C and δ 15 N values of proteinogenic AAs have been used as powerful tools for studying food web structures, trophic relationships, and biogeochemical processes in the ecosystem (see Ohkouchi et al 2017, 1 Whiteman et al 2019, 2 Yun et al 2022, 3 and Ohkouchi 2023 4 for general reviews). The δ 13 C values of AAs are “fingerprints” of the biosynthetic sources of AAs and are used to trace the carbon sources in food webs, 5–7 and δ 15 N values of AAs can be used to calculate the trophic positions of species and to reconstruct the food web structures in aquatic and terrestrial ecosystems 8–11 …”

“…tools for studying food web structures, trophic relationships, and biogeochemical processes in the ecosystem (see Ohkouchi et al 2017, 1 Whiteman et al 2019, 2 Yun et al 2022, 3 and Ohkouchi 2023 4 for general reviews). The δ 13 C values of AAs are "fingerprints" of the biosynthetic sources of AAs and are used to trace the carbon sources in food webs, [5][6][7] and δ 15 N values of AAs can be used to calculate the trophic positions of species and to reconstruct the food web structures in aquatic and terrestrial ecosystems.…”

Stepwise Approach for Tracing the Geographical Origins of the Manila Clam Ruditapes philippinarum Using Dual-Element Isotopes and Carbon Isotopes of Fatty Acids

“…The CSIA approach may overcome some of the limitations arising from bulk element isotopes that represent an integrated value analyzed in a sample [62]. This approach has been used in ecological and archaeological studies in recent years [63,64]. CSIA-FA can be utilized in various fields, such as food chain research, because it provides information on both FA composition and stable isotope ratios [32].…”