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

Compound‐specific stable isotope analysis of individual amino acids (CSIA‐AA) has emerged as a transformative approach to estimate consumer trophic positions (TPCSIA) that are internally indexed to primary producer nitrogen isotope baselines. Central to accurate TPCSIAestimation is an understanding of beta (β) values—the differences between trophic and source AA δ15N values in the primary producers at the base of a consumers’ food web. Growing evidence suggests higher taxonomic and tissue‐specificβvalue variability than typically appreciated.

This meta‐analysis fulfils a pressing need to comprehensively evaluate relevant sources ofβvalue variability and its contribution to TPCSIAuncertainty. We first synthesized all published primary producer AA δ15N 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 δ15N andβvalue variability. Lastly, we evaluated the sensitivity of TPCSIAestimates to uncertainty in meanβGlx‐Phevalues and Glx‐Phe trophic discrimination factors (TDFGlx‐Phe).

We show that variation inβGlx‐Phevalues 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 toβGlx‐Phevalue variability, but we found no clear distinction among C3, C4and CAM plantβGlx‐Phevalues. Notably, we found that vascular plantβGlx‐Lysvalues (+2.5 ± 1.6‰) are considerably less variable thanβGlx‐Phevalues, making Lys a useful AA tracer of primary production sources in terrestrial systems. Our multi‐trophic level sensitivity analyses demonstrate that TPCSIAestimates are highly sensitive to changes in bothβGlx‐Pheand TDFGlx‐Phevalues but that the relative influence ofβvalues dissipates at higher trophic levels.

Our results highlight that primary producerβvalues are integral to accurate trophic position estimation. We outline four key recommendations for identifying, constraining and accounting forβvalue variability to improve TPCSIAestimation accuracy and precision moving forward. We must ultimately expand libraries of primary producer AA δ15N values to better understand the mechanistic drivers ofβvalue variation.

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Award ID(s):
1907144 2049307
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Date Published:
Journal Name:
Methods in Ecology and Evolution
Medium: X Size: p. 1750-1767
["p. 1750-1767"]
Sponsoring Org:
National Science Foundation
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