title: Factors Controlling the Stable Nitrogen Isotopic Composition (δ15N) of Lipids in Marine Animals.
abstract: Lipid extraction of biomass prior to stable isotope analysis is known to cause variable changes in the stable nitrogen isotopic composition (δ15N) of residual biomass. However, the underlying factors causing these changes are not yet clear. Here we address this issue by comparing the δ15N of bulk and residual biomass of several marine animal tissues (fish, crab, cockle, oyster, and polychaete), as well as the δ15N of the extracted lipids. As observed previously, lipid extraction led to a variable offset in δ15N of biomass (differences ranging from -2.3 to +1.8 ‰). Importantly, the total lipid extract (TLE) was highly depleted in 15N compared to bulk biomass, and also highly variable (differences ranging from -14 to +0.7 ‰). The TLE consisted mainly of phosphatidylcholines, a group of lipids with one nitrogen atom in the headgroup. To elucidate the cause for the 15N-depletion in the TLE, the δ15N of amino acids was determined, including serine because it is one of the main sources of nitrogen to N-containing lipids. Serine δ15N values differed by -7 to +2 ‰ from bulk biomass δ15N, and correlated well with the 15N depletion in TLEs. On average, serine was less depleted (-3‰) than the TLE (-7 ‰), possibly due to fractionation during biosynthesis of N-containing headgroups, or that other nitrogen-containing compounds, such as urea and choline, or recycled nitrogen contribute to the nitrogen isotopic composition of the TLE. The depletion in 15N of the TLE relative to biomass increased with the trophic level of the organisms.
authors.affiliation: Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, Den Burg (Texel), The Netherlands.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Svensson
authors.affiliation: Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, Den Burg (Texel), The Netherlands.|Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schouten
authors.affiliation: Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, Den Burg (Texel), The Netherlands.
authors.forename: Ellen C
authors.initials: EC
authors.lastname: Hopmans
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Jack J
authors.initials: JJ
authors.lastname: Middelburg
authors.affiliation: Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, Den Burg (Texel), The Netherlands.|Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Jaap S
authors.initials: JS
authors.lastname: Sinninghe Damsté
mesh_terms: D000818:Animals; D003386:Brachyura / Q000378:metabolism; D002247:Carbon Isotopes / Q000032:analysis; D049873:Cardiidae / Q000378:metabolism; D005399:Fishes / Q000378:metabolism; D008055:Lipids / Q000737:chemistry*; D009587:Nitrogen Isotopes / Q000032:analysis*; D011077:Polychaeta / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D008055:Lipids; D009587:Nitrogen Isotopes