Portal de Periódicos da CAPES

Meta‐analysis of primary producer amino acid δ 15 N values and their influence on trophic position estimation

2021; Wiley; Volume: 12; Issue: 10 Linguagem: Inglês

10.1111/2041-210x.13678

2041-210X

Matthew D. Ramirez, Alexi C. Besser, Seth D. Newsome, Kelton W. McMahon,

Microbial Community Ecology and Physiology

Abstract Compound‐specific stable isotope analysis of individual amino acids (CSIA‐AA) has emerged as a transformative approach to estimate consumer trophic positions (TP CSIA ) that are internally indexed to primary producer nitrogen isotope baselines. Central to accurate TP CSIA estimation is an understanding of beta ( β ) values—the differences between trophic and source AA δ 15 N values in the primary producers at the base of a consumers’ food web. Growing evidence suggests higher taxonomic and tissue‐specific β value variability than typically appreciated. This meta‐analysis fulfils a pressing need to comprehensively evaluate relevant sources of β value variability and its contribution to TP CSIA uncertainty. We first synthesized all published primary producer AA δ 15 N data to investigate ecologically relevant sources of variability (e.g. taxonomy, tissue type, habitat type, mode of photosynthesis). We then reviewed the biogeochemical mechanisms underpinning AA δ 15 N and β value variability. Lastly, we evaluated the sensitivity of TP CSIA estimates to uncertainty in mean β Glx‐Phe values and Glx‐Phe trophic discrimination factors (TDF Glx‐Phe ). We show that variation in β Glx‐Phe values is two times greater than previously considered, with degree of vascularization, not habitat type (terrestrial vs. aquatic), providing the greatest source of variability (vascular autotroph = −6.6 ± 3.4‰; non‐vascular autotroph = +3.3 ± 1.8‰). Within vascular plants, tissue type secondarily contributed to β Glx‐Phe value variability, but we found no clear distinction among C 3 , C 4 and CAM plant β Glx‐Phe values. Notably, we found that vascular plant β Glx‐Lys values (+2.5 ± 1.6‰) are considerably less variable than β Glx‐Phe values, making Lys a useful AA tracer of primary production sources in terrestrial systems. Our multi‐trophic level sensitivity analyses demonstrate that TP CSIA estimates are highly sensitive to changes in both β Glx‐Phe and TDF Glx‐Phe values but that the relative influence of β values dissipates at higher trophic levels. Our results highlight that primary producer β values are integral to accurate trophic position estimation. We outline four key recommendations for identifying, constraining and accounting for β value variability to improve TP CSIA estimation accuracy and precision moving forward. We must ultimately expand libraries of primary producer AA δ 15 N values to better understand the mechanistic drivers of β value variation.