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Factors Controlling the Stable Nitrogen Isotopic Composition (δ15N) of Lipids in Marine Animals
Svensson, E.; Schouten, S.; Hopmans, E.C.; Middelburg, J.J.; Sinninghe Damsté, J.S. (2016). Factors Controlling the Stable Nitrogen Isotopic Composition (δ15N) of Lipids in Marine Animals. PLoS One 11(1): e0146321. dx.doi.org/10.1371/journal.pone.0146321
In: PLoS One. Public Library of Science: San Francisco. ISSN 1932-6203, more
Peer reviewed article  

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  • Middelburg, J.J., more
  • Sinninghe Damsté, J.S., more

Abstract
    Lipid extraction of biomass prior to stable isotope analysis is known to cause variablechanges in the stable nitrogen isotopic composition (d15N) of residual biomass. However,the underlying factors causing these changes are not yet clear. Here we address this issueby comparing the d15N of bulk and residual biomass of several marine animal tissues (fish,crab, cockle, oyster, and polychaete), as well as the d15N of the extracted lipids. Asobserved previously, lipid extraction led to a variable offset in d15N of biomass (differencesranging from -2.3 to +1.8‰). Importantly, the total lipid extract (TLE) was highly depleted in15N 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 nitrogenatom in the headgroup. To elucidate the cause for the 15N-depletion in the TLE, thed15N of amino acids was determined, including serine because it is one of the main sourcesof nitrogen to N-containing lipids. Serine d15N values differed by -7 to +2‰from bulk biomassd15N, and correlated well with the 15N depletion in TLEs. On average, serine was lessdepleted (-3‰) than the TLE (-7‰), possibly due to fractionation during biosynthesis of Ncontainingheadgroups, or that other nitrogen-containing compounds, such as urea andcholine, or recycled nitrogen contribute to the nitrogen isotopic composition of the TLE. Thedepletion in 15N of the TLE relative to biomass increased with the trophic level of theorganisms.

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