Dataset Information

Factors Controlling the Stable Nitrogen Isotopic Composition (?15N) 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 (?15N) of residual biomass. However, the underlying factors causing these changes are not yet clear. Here we address this issue by comparing the ?15N of bulk and residual biomass of several marine animal tissues (fish, crab, cockle, oyster, and polychaete), as well as the ?15N of the extracted lipids. As observed previously, lipid extraction led to a variable offset in ?15N 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 ?15N of amino acids was determined, including serine because it is one of the main sources of nitrogen to N-containing lipids. Serine ?15N values differed by -7 to +2 ‰ from bulk biomass ?15N, 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.

SUBMITTER: Svensson E

PROVIDER: S-EPMC4701503 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Factors Controlling the Stable Nitrogen Isotopic Composition (δ15N) of Lipids in Marine Animals.

Svensson Elisabeth E Schouten Stefan S Hopmans Ellen C EC Middelburg Jack J JJ Sinninghe Damsté Jaap S JS

PloS one 20160105 1

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 variabl ...[more]

PMID: 26731720

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Project description:BackgroundBrazil is a low- to medium-income country and has the second largest pet food market in the world with 8% of world pet food consumption. The lowest-income social class spends around 17% of their domestic budget on pet food and other items related to pets. Consumers are frequently misled by advertising as there is no precise information about the main sources of protein, carbohydrates and fat in the labels, and the Brazilian pet food industry can legally claim that their products contain certain items like salmon or beef even if they use just a flavoring compound.MethodsThe stable isotope methodology compares the stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N) between source and product. The 13C/12C ratio of a specific product (e.g., dog food) reveals the proportions of C4 (maize) and C3 (soybean, rice and wheat) plants in that product and the 15N/14N ratio reveals the proportion of the compounds derived from animals. With this isotopic data, we used MixSIAR, a Bayesian stable isotope-mixing model, to estimate the proportion of maize, grains, poultry and beef in dog food.ResultsThe δ13C values of dry dog food ranged from -24.2‰ to -12.8‰, with an average (± standard-deviation) of -17.1‰ ± 2.8‰. The δ13C values of wet pet food ranged from -25.4‰ to -16.9‰, with an average (± standard-deviation) of -21.2‰ ± 2.4‰, which was significantly lower (p < 0.01). The δ15N values of the dry and wet food ranged from 1.7‰ to 4.2‰, and from 0.5‰ to 5.5‰, respectively. The average δ15N values of dry food (2.9‰ ± 0.5‰) was not higher than the wet food (2.6‰ ± 1.3‰) (p > 0.01). The output of the MixSIAR showed a low proportion of bovine products in dry dog food samples. On the other hand, poultry was obviously the dominant ingredient present in most of the samples. Maize was the second dominant ingredient. Wet and dry dog food showed similar isotopic analysis results. The only difference was a lower proportion of maize and higher proportion of grains in wet dog food.DiscussionThe main finding is that dog food in Brazil is mostly made of approximately 60% (ranging from 32% to 86%) animal-based and 40% (ranging from 14% to 67%) plant-based products. Poultry and maize are the main ingredients. Poultry is added as a by-product or meal, which avoids competition between dogs and humans for meat products, while they can compete for maize. On the other hand, a large proportion of plant-based products in dog food decreases the energy and environmental footprint, since plant-based food products tend to be less harmful compared to animal-based products. Labels can mislead consumers by showing pictures of items that are not necessarily part of the product composition and by not showing the detailed information on the proportion of each ingredient. This information would allow customers to make their own choices considering their pet's nutrition, the competition between animals and humans for resources and environmental sustainability.

Project description:Nitrogen stable isotope (15N) natural abundance is widely used to study nitrogen cycling. In grazed ecosystems, urine patches are hot-spots of nitrogen inputs, losses, and changes in δ15N. Understanding δ15N dynamics in urine-affected vegetation is therefore crucial for accurate inferences from 15N natural abundance in grasslands. We hypothesized that leaf δ15N following urine deposition varies with time and plant functional group. Specifically, we expected (i) short-term decreases in δ15N due to foliar absorption of 15N-depleted volatilized ammonia, (ii) followed by increases in δ15N due to uptake of 15N-enriched soil inorganic nitrogen, and (iii) that the magnitude of these changes is less in legumes than in grasses. The latter should be expected because ammonia absorption depends on leaf nitrogen concentration, which is higher in legumes than grasses, and because biological nitrogen fixation will modify the influence of urine-derived nitrogen on δ15N in legumes. We applied cattle urine to a mixture of Lolium perenne and Trifolium repens in a pot experiment. Nitrogen concentration and δ15N were determined for successive leaf cohorts and bulk biomass either 17 (early) or 32 (late) days after urine application. Early after urine application, leaves of L. perenne were 15N-depleted compared to control plants (δ15N 0.1 vs. 5.8‰, respectively), but leaves of T. repens were not (-1.1 vs. -1.1‰, respectively). Later, both species increased their δ15N, but T. repens (4.5‰) less so than L. perenne (5.9‰). Vegetation sampled within and outside urine patches in the field further supported these results. Our findings confirm that foliar ammonia uptake can substantially decrease grass foliar δ15N, and that in both grass and legume the direction of the δ15N response to urine changes over time. Temporal dynamics of plant δ15N at urine patches therefore need to be explicitly addressed when 15N natural abundance is used to study nitrogen cycling in grazed grasslands.

Dataset Information

Factors Controlling the Stable Nitrogen Isotopic Composition (?15N) of Lipids in Marine Animals.

Publications

Factors Controlling the Stable Nitrogen Isotopic Composition (δ15N) of Lipids in Marine Animals.

Similar Datasets

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