Isotopic Signatures Of Nitrogen Research Articles

Effect of adult feeding on the δ15N signatures of different tissues for Popillia japonica

AbstractAs insects feed, stable isotopes from their diets are assimilated into their tissues. Stable isotopes provide a method to determine what insects are feeding on, and in some cases, where the insects have been feeding. One method for evaluating what adult holometabolous insects fed on as larvae, is to sample tissues from the integument of the adult. The integument should have isotopic signatures that reflect the diet of the larvae, and these inert tissues should be less influenced by adult feeding compared to other tissues. The objective of our research was to examine how isotopic signatures of nitrogen in various tissues of adult Popillia japonica (Newman) (Coleoptera: Scarabaeidae) beetles would be influenced by adults feeding on 15N‐enriched plant material. We collected adults from emergences cages at unenriched grasses and fed them for 0, 2, 5, or 10 days with grape plants fertilized with isotopically enriched or unenriched potassium nitrate. The δ15N signature of elytra and soft tissues both increased over time when fed enriched plant material. The δ15N signatures of soft tissues were higher than that of the elytra over time. Adult beetles fed highly enriched plant material displayed increased δ15N signatures over time of tissues generally considered metabolically inactive, which suggests that adult feeding does contribute to the isotopic signatures of elytra tissue. The difference between the δ15N signatures of soft tissues and elytra demonstrates a lower turnover rate in the elytra and highlights the fact that diet does contribute to the signature of elytra.

Stable isotope analyses reveal unique trophic role of reef manta rays (Mobula alfredi) at a remote coral reef.

Stable isotope analyses provide the means to examine the trophic role of animals in complex food webs. Here, we used stable isotope analyses to characterize the feeding ecology of reef manta rays (Mobula alfredi) at a remote coral reef in the Western Indian Ocean. Muscle samples of M. alfredi were collected from D'Arros Island and St. Joseph Atoll, Republic of Seychelles, in November 2016 and 2017. Prior to analysis, lipid and urea extraction procedures were tested on freeze-dried muscle tissue in order to standardize sample treatment protocols for M. alfredi. The lipid extraction procedure was effective at removing both lipids and urea from samples and should be used in future studies of the trophic ecology of this species. The isotopic signatures of nitrogen (δ15N) and carbon (δ13C) for M. alfredi differed by year, but did not vary by sex or life stage, suggesting that all individuals occupy the same trophic niche at this coral reef. Furthermore, the isotopic signatures for M. alfredi differed to those for co-occurring planktivorous fish species also sampled at D'Arros Island and St. Joseph Atoll, suggesting that the ecological niche of M. alfredi is unique. Pelagic zooplankton were the main contributor (45%) to the diet of M. alfredi, combined with emergent zooplankton (38%) and mesopelagic prey items (17%). Given the extent of movement that would be required to undertake this foraging strategy, individual M. alfredi are implicated as important vectors of nutrient supply around and to the coral reefs surrounding D'Arros Island and St. Joseph Atoll, particularly where substantial site fidelity is displayed by these large elasmobranchs.

Stable isotopic evidence for the differential contribution of diazotrophs to the epipelagic grazing food chain in the mid‐Pacific Ocean

AbstractAimBiological nitrogen fixation supports primary production in oligotrophic water, but its link to higher trophic levels has not been described fully on a biogeographical basis. Here, we determine the regional patterns of the contribution of the combined nitrogen to biological production within the epipelagic layer of the mid‐Pacific Ocean using the isotopic signatures of nitrogen (δ15N) and carbon (δ13C) in the biological components.LocationThe mid‐Pacific Ocean along 170° W between the southern subtropical front and the Chukchi Sea.Time periodNorthern and austral summer in 2013 and 2014.Major taxa studiedPlanktonic and micronektonic biota in the euphotic layer.MethodsWe measured the geographical variations in δ15N and δ13C of the suspended particulate organic matter (POM), mesozooplankton assemblage and micronektonic fish. We analysed the relationships among these values and the environmental variables of temperature, nitrate concentration and biological nitrogen fixation activity along a 12,000‐km meridional transect.ResultsThe POM δ15N at 0 m was negatively correlated with in situ N2 fixation activity in the subtropical region, whereas that in the equatorial and high‐latitude regions was correlated with the nitrate concentration at 0 m. We found that the ratios of the increase in δ15N to δ13C along the grazing food chain were consistent throughout the equatorial and subtropical regions. Cluster analyses based on the stable isotopic signatures in the biotic components revealed that the food chains in the stations within the subtropical mid‐Pacific Ocean were separated into three groups based on the differential contributions of biological nitrogen fixation.Main conclusionsDistinct food chains from primary to tertiary production sustained by different nitrogen sources, nitrate below the euphotic zone, and diazotrophic nitrogen occur within the same biogeographical provinces in the subtropical mid‐Pacific Ocean. The diazotroph‐dominant community contributes substantially to the apex predators in the central areas of the subtropical gyres.

Fate and Trophic Transfer of Rare Earth Elements in Temperate Lake Food Webs.

Many mining projects targeting rare earth elements (REE) are in development in North America, but the background concentrations and trophic transfer of these elements in natural environments have not been well characterized. We sampled abiotic and food web components in 14 Canadian temperate lakes unaffected by mines to assess the natural ecosystem fate of REE. Individual REE and total REE concentrations (sum of individual element concentrations, ΣREE) were strongly related with each other throughout different components of lake food webs. Dissolved organic carbon and dissolved oxygen in the water column, as well as ΣREE in sediments, were identified as potential drivers of aqueous ΣREE. Log10 of median bioaccumulation factors ranged from 1.3, 3.7, 4.0, and 4.4 L/kg (wet weight) for fish muscle, zooplankton, predatory invertebrates, and nonpredatory invertebrates, respectively. [ΣREE] in fish, benthic macroinvertebrates, and zooplankton declined as a function of their trophic position, as determined by functional feeding groups and isotopic signatures of nitrogen (δ15N), indicating that REE were subject to trophic dilution. Low concentrations of REE in freshwater fish muscle compared to their potential invertebrate prey suggest that fish fillet consumption is unlikely to be a significant source of REE to humans in areas unperturbed by mining activities. However, other fish predators (e.g., piscivorous birds and mammals) may accumulate REE from whole fish as they are more concentrated than muscle. Overall, this study provides key information on the baseline concentrations and trophic patterns for REE in freshwater temperate lakes in Quebec, Canada.

Using dual isotopes to identify sources and transformations of nitrogen in water catchments with different land uses, Loess Plateau of China.

Nitrogen pollution in rivers is a research hotspot in the field of biogeochemistry. However, the types and sources of pollution have historically been poorly understood in the water catchments of the Loess Plateau in China. In this study, we have chosen the main waterway and four lesser branches of the Jinghe River that vary by land use. We investigated the concentrations and isotopic signatures of nitrogen in river water. Our results revealed that nitrate was the dominant nitrogen type in river catchments of the Loess Plateau. The δ(15)N and δ(18)O values showed that NO3 (-) ions in the studied river samples were derived from precipitation, manure, sewage, soil organic nitrogen, and synthetic NO3 (-) fertilizer. The δ(18)O-NO3 (-) values during July 2012 (mean ± SD = +18.1 ± 1.5‰) were higher than those during the September 2013 (mean ± SD = +7.8 ± 3.7‰), which indicated that mixing with atmospheric NO3 (-) resulted in the high δ(18)O values during July 2012. It appears that no intense nitrification and denitrification occurred in all five rivers according to the isotopic and chemical data. A Bayesian model was used to determine the contributions of four NO3 (-) sources to all five rivers. Results showed that source contributions differ significantly between July and September, and the four potential NO3 (-) sources also showed high variability between the different land use areas.

Signatures of the martian atmosphere in glass of the Zagami meteorite.

Isotopic signatures of nitrogen, argon, and xenon have been determined in separated millimeter-sized pockets of shock-melted glass in a recently identified lithology of the meteorite Zagami, a shergottite. The ratio of nitrogen-15 to nitrogen-14, which is at least 282 per mil larger than the terrestrial value, the ratio of xenon-129 to xenon-132 = 2.40, and the argon isotopic abundances match the signatures previously observed in the glassy lithology of the Antarctic shergottite EETA 79001. These results show that the signatures in EETA 79001 are not unique but characterize the trapped gas component in shock-melted glass of shergottites. The isotopic and elemental ratios of nitrogen, argon, and xenon closely resemble the Viking spacecraft data for the martian atmosphere and provide compelling evidence for a martian origin of the two shergottites and, by extension, of the meteorites in the shergottites-nakhlites-chassignites (SNC) group.