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The nitrogen deficiency in steels measured by atom probe tomography (APT) is considered to arise from the obscurement of singly charged dimer nitrogen ions (N2+) by the iron-dominant peak (56Fe2+) at 28 Da. To verify this by quantifying the amount of N2+ ions, γ′-Fe4N consisting of the 15N isotope was prepared on iron substrates by plasma nitriding using a nitrogen isotopic gas (15N2). Although considerable amounts of 15N2+ were observed at 30 Da without overlap with any iron peak, the observed nitrogen concentrations of γ′-Fe4N were clearly lower than the stoichiometric composition (19–20 at%), using both pulsed voltage and pulsed laser atom probes. The origin of the missing nitrogen, excluding nitrogen obscured by other ion species, was predicted to be the occurrence of neutral nitrogen or nitrogen gas molecules in field evaporation. The generation rate of iron nitride ions (FeN2+) for 15N was significantly lower than that for 14N in γ′-Fe4N, which affected the amount of the missing nitrogen. The isotope effect suggests that the isotopic ratio cannot always be determined from only one ion species among the multiple species observed in the APT analysis. We discuss the mechanism of the isotope effect in FeN2+ formation by field evaporation.

Ammonium nitrate (AN) is one of the most commonly used explosives in criminal cases. The comparison and source-tracing of AN is important for investigation of attribution and fingerprinting of an explosive used at different events. The stable isotope signature of AN is an important index for comparison and tracing. However, the characteristics of the stable nitrogen isotopic ratios of AN (δ15 NNH4NO3 ) alone are not sufficient to achieve a fine comparison between different AN samples. To increase the comparison index and further improve the discriminability between stable nitrogen isotopic ratios of different ANs, a method of isolation and analysis of nitrate ions in AN was established using stable-isotope-ratio mass spectrometry (IRMS). The method was based on the principle that strong alkali react with AN to produce ammonia and nitrate. After the isolation, stable nitrogen isotopes of nitrate ions (δ15 NNO3 ) were obtained using IRMS, and then the stable nitrogen isotopes of ammonium ions from AN (δ15 NNH4 ) was calculated according to the principle of mass balance. The results show that the method is effective for the isolation of nitrate ions without notable isotope fractionation. The developed method was applied to analyze and discriminate AN samples from eight different cities in China. Three samples out of the initial eight AN samples with similar δ15 NNH4NO3 values were further distinguished by their δ15 NNH4 and δ15 NNO3 values. The isolation and stable-nitrogen isotopic analysis method developed for nitrate ions in AN is simple and effective, thereby increasing the discriminability of the stable isotope ratios in AN.

While plant δ15 N values have been applied to understand nitrogen (N) dynamics, uncertainties regarding intraspecific and temporal variability currently limit their application. We used a 28 yr record of δ15 N values from two Mojave Desert populations of Encelia farinosa to clarify sources of population-level variability. We leveraged > 3500 foliar δ15 N observations collected alongside structural, physiological, and climatic data to identify plant and environmental contributors to δ15 N values. Additional sampling of soils, roots, stems, and leaves enabled assessment of the distribution of soil N content and δ15 N, intra-plant fractionations, and relationships between soil and plant δ15 N values. We observed extensive within-population variability in foliar δ15 N values and found plant age and foliar %N to be the strongest predictors of individual δ15 N values. There were consistent differences between root, stem, and leaf δ15 N values (spanning c. 3‰), but plant and bulk soil δ15 N values were unrelated. Plant-level variables played a strong role in influencing foliar δ15 N values, and interannual relationships between climate and δ15 N values were counter to previously recognized spatial patterns. This long-term record provides insights regarding the interpretation of δ15 N values that were not available from previous large-scale syntheses, broadly enabling more effective application of foliar δ15 N values.

Estimating stable isotopic offset values is crucial for dietary reconstructions. Although research into stable isotope ecology of wild nonhuman primates is increasing overall, only a minority of studies involve laboratory experiments. This study is the first to report the carbon and nitrogen stable isotopic offset values in hair and feces of orangutans. During an experiment lasting 1 week, the weight of each consumed food item was recorded for each of six captive Bornean orangutan (Pongo pygmaeus) individuals. The food, hair, and fecal samples were collected for a few days, and their stable carbon and nitrogen isotope ratios were measured using an elemental analyzer/isotope ratio mass spectrometer. Subsamples of feces were treated with ethanol during the preservation process. Monte Carlo analyses showed that the 95% confidence intervals (CIs) of the carbon and nitrogen offset values between hair and diet were +0.9‰ to +3.9‰ and +2.3‰ to +4.5‰, respectively. The 95% CIs of the carbon and nitrogen offset values between feces and diet were −3.7‰ to −0.9‰ and +0.3‰ to +2.7‰, respectively. The effect of ethanol treatment on the stable isotope ratios of feces was unclear and inconclusive. The computed offset values of hair in captive orangutans are similar to those reported in other nonhuman primates, although those of feces showed greater interspecies variations. The offset values estimated in this study contribute to isotopic studies into the feeding ecology of free-ranging orangutans who are critically endangered in most wild settings.

The availability of nitrogen (N) in ocean surface waters affects rates of photosynthesis and marine ecosystem structure. In spite of low dissolved inorganic N concentrations, export production in oligotrophic waters is comparable to more nutrient replete regions. Prior observations raise the possibility that di-nitrogen (N2) fixation supplies a significant fraction of N supporting export production in the Gulf of Mexico. In this study, geochemical tools were used to quantify the relative and absolute importance of both subsurface nitrate and N2 fixation as sources of new N fueling export production in the oligotrophic Gulf of Mexico in May 2017 and May 2018. Comparing the isotopic composition (“δ15N”) of nitrate with the δ15N of sinking particulate N collected during five sediment trap deployments each lasting two to four days indicates that N2 fixation is typically not detected and that the majority (≥80%) of export production is supported by subsurface nitrate. Moreover, no gradients in upper ocean dissolved organic N and suspended particulate N concentration and/or δ15N were found that would indicate significant N2 fixation fluxes accumulated in these pools, consistent with low Trichodesmium spp. abundance. Finally, comparing the δ15N of sinking particulate N captured within vs. below the euphotic zone indicates that during late spring regenerated N is low in δ15N compared to sinking N.

The isotopic composition of nitrogen and oxygen in nitrogen dioxide (NO2) potentially carries a wealth of information about the dynamics of the nitrogen oxides (NOx = nitric oxide (NO) + NO2) chemistry in the atmosphere. While nitrogen isotopes of NO2 are subtle indicators of NOx emissions and chemistry, oxygen isotopes are believed to reflect only the O3 / NOx / VOC chemical regime in different atmospheric environments. In order to access this potential tracer of the tropospheric chemistry, we have developed an efficient active method to trap atmospheric NO2 on denuder tubes and measured, for the first time, its multi-isotopic composition (δ15N, δ18O, and Δ17O). The Δ17O values of NO2 trapped at our site in Grenoble, France, show a large diurnal cycle peaking in late morning at (39.2 ± 0.3) ‰ and decreasing at night until (20.5 ± 0.3) ‰. On top of this diurnal cycle, Δ17O also exhibits substantial daytime variability (from 29.7 ‰ to 39.2 ‰), certainly driven by changes in the O3 to peroxyl radicals (RO2) ratio. The nighttime decay of Δ17O(NO2) appears to be driven by NO2 slow removal, mostly from conversion into N2O5, and its formation from the reaction between O3 and freshly emitted NO. As expected from a nighttime Δ17O(NO2) expression, our Δ17O(NO2) measured towards the end of the night is quantitatively consistent with typical values of Δ17O(O3). Daytime N isotope fractionation is estimated using a general expression linking it to Δ17O(NO2). An expression is also derived for the nighttime N isotope fractionation. In contrast to Δ17O(NO2), δ15N(NO2) measurements exhibit little diurnal variability (−11.8 ‰ to −4.9 ‰) with negligible isotope fractionations between NO and NO2, mainly due to high NO2 / NOx ratios, excepted during the morning rush hours. The main NOx emission sources are estimated using a Bayesian isotope mixing model, indicating the predominance of traffic emissions in this area. These preliminary results are very promising for using the combination of Δ17O and δ15N of NO2 as a probe of the NOx sources and fate and for interpreting nitrate isotopic composition records.

The aim of this study is to determine the stable isotope ratios of anchovy caught in the Black Sea and Marmara Sea. Stable carbon and nitrogen isotope ratios (δ13C, δ15N) of European anchovy (Engraulis encrasicolus) were estimated at four sampling sites (İğneada, İstanbul, Trabzon and Hopa) in the Black Sea and Marmara Sea (Turkey). δ13C and δ15N values of European anchovy ranged from -22.31 to -19.19 ‰ and from 3.81 to 12.79 ‰, while C/N ratios ranged from 2.01 to 6.21 in muscle tissue of European anchovy, respectively. İğneada station had more depleted δ13C values and more enriched δ15N values than other stations. This difference might be due to the terrestrial input and agricultural activities in this region.

Nitrogen fertiliser application can effectively increase the net primary productivity (NPP) of agriculture and grassland ecosystems. There is some long-term retention of nitrogen applied to soils, ...

Dissimilatory nitrate reduction (DNR) to nitrite is the first step in denitrification, the main process through which bioavailable nitrogen is removed from ecosystems. DNR is catalyzed by both cytosolic (Nar) and periplasmic (Nap) nitrate reductases and fractionates the stable isotopes of nitrogen (14N, 15N) and oxygen (16O, 18O), which is reflected in residual environmental nitrate pools. Data on the relationship between the pattern in oxygen vs nitrogen isotope fractionation (18e/15e) suggests that systematic differences exist between marine and terrestrial ecosystems that are not fully understood. We examined the 18e/15e of nitrate-reducing microorganisms that encode Nar, Nap, or both enzymes, as well as gene deletion mutants of Nar and Nap to test the hypothesis that enzymatic differences alone could explain the environmental observations. We find that the distribution of 18e/15e fractionation ratios of all examined nitrate reductases forms two distinct peaks centered around an 18e/15e proportionality of 0.55 (Nap) and 0.91 (Nar), with the notable exception of the Bacillus Nar reductases, which cluster isotopically with the Nap reductases. Our findings may explain differences in 18e/15e fractionation between marine and terrestrial systems and challenge current knowledge about Nar 18e/15e signatures.

The nitrogen isotope exchange reaction was applied to measure the interfacial reaction rate constant of nitrogen with liquid cobalt at 1823 K, 1873 K, and 1923 K. Measured values increased with increasing temperature, with average values of 1.3×10−7 mol cm−2 s−1 atm−1 at 1823 K, 3.3×10−7 mol cm−2 s−1 atm−1 at 1873 K, and 6.2×10−7 mol cm−2 s−1 atm−1 at 1923 K. Compared with liquid iron, the rate on cobalt is more than an order of magnitude smaller.

Ammonium (NH4+), ammonia (NH3) and N2 are key nitrogen species in geological nitrogen recycling. NH3 has also been proposed to play an important role in mobilizing base metals in the form of metal-ammine complexes in hydrothermal fluids. The nitrogen isotope fractionation factors among these nitrogen species in aqueous and gaseous phases are essential parameters to trace source signatures and geochemical properties in geological processes. However, the nitrogen isotope fractionation factors for metal-ammine complexes are largely absent, and the few existing nitrogen isotope fractionation factors for the aqueous NH4+ – aqueous NH3 pair show large discrepancy between experimental results and theoretical calculations. In this study, we employed the density functional theory to systematically calculate the nitrogen isotope fractionation factors among the nitrogen species that may occur in a hydrothermal system, i.e., gaseous N2, gaseous and aqueous NH4+ and NH3, and ammine complexes of Co, Zn, Cu, Cd, Ag, Au, and Pt. Based on these new results, the large nitrogen isotope fractionations for the aqueous NH4+ – aqueous NH3 pair observed in previous experimental studies can be well explained by a combined effect of an equilibrium isotope fractionation between aqueous NH4+ and aqueous NH3 and a kinetic isotope fractionation during NH3 degassing from the solution. This suggests that the nitrogen isotopic behavior during NH3 degassing in natural hydrothermal system can be more complicated than previous thought. A numeric model is thus established here to quantify the combined isotopic effect on partial NH3 degassing. Using the new results of metal-ammine complexes, we also tested the hypothesis that nitrogen mobilization could be controlled by copper-ammine complex based on the copper concentration-δ15N relationship previously observed in meta-gabbros.

Plants acquire multiple resources from the environment and may need to adjust and/or balance their respective resource-use efficiencies to maximize grow and survival, in a locally adaptive manner. In this study, tissue and whole-plant carbon (C) isotopic composition (δ13C) and carbon/nitrogen (C/N) ratios provided long-term measures of use efficiencies for water (WUE) and nitrogen (NUE), and a nitrogen (N) isotopic composition (δ15N)-based mass balance model was used to estimate traits related to N uptake and assimilation in heart-leaved willow (Salix eriocephala Michx.). In an initial common garden experiment consisting of 34 populations, we found population-level variation in δ13C, C/N ratio and δ15N, indicating different patterns in WUE, NUE and N uptake and assimilation. Although there was no relationship between foliar δ13C and C/N ratios among populations, there was a significant negative correlation between these measures across all individuals, implying a genetic and/or plastic trade-off between WUE and NUE not associated with local adaptation. To eliminate any environmental effect, we grew a subset of 21 genotypes hydroponically with nitrate as the sole N source and detected significant variation in δ13C, δ15N and C/N ratios. Variation in δ15N was mainly due to genotypic differences in the nitrate efflux/influx ratio (E/I) at the root. Both experiments suggested clinal variation in δ15N (and thus N uptake efficiency) with latitude of origin, which may relate to water availability and could contribute to global patterns in ecosystem δ15N. There was a tendency for genotypes with higher WUE to come from more water-replete sites with shorter and cooler growing seasons. We found that δ13C, C/N ratio and E/I were not inter-correlated, suggesting that the selection of growth, WUE, NUE and N uptake efficiency can occur without trade-off.

Redox transformations of nitrogen (N) play a critical role in determining its speciation and biological availability, thus defining the magnitude and extent of productivity in many ecosystems. A range of important nitrogen transformations often co-occur in regions hosting other redox-active elements, including sulfur, iron, and manganese (Mn), especially along sharp redox gradients within aquatic sediments. This proximity in “redox real estate” produces conditions under which multi-element interactions and coupled cycling are thermodynamically favored. While previous work has reported anoxic nitrification linked to the presence of manganese (Mn) oxides in sediments, a clear connection between the cycling of Mn and N has remained elusive. Soluble Mn(III), which is stabilized via ligand-complexation, has recently been shown to represent the dominant dissolved Mn species in many environments. Here, we examined the reactivity of ligand-stabilized Mn(III) with nitrite, using natural abundance stable nitrogen and oxygen isotopes to explore reaction dynamics under a range of conditions. Oxidation of nitrite to nitrate by Mn(III)-pyrophosphate proceeded abiotically under both oxygen replete and nitrogen-purged conditions. Kinetics and isotope systematics of this reaction were measured over a range of pH (5–8), with reaction rates decreasing with increasing pH. Under all treatments, an inverse kinetic isotope effect of −19.9 ± 0.7‰ was observed for N, remarkably similar to previously documented fractionation by nitrite-oxidizing organisms. Experiments using 18O-labeled water confirmed that the source of the additional oxygen atom was from water. These findings suggest that nitrite oxidation in environments hosting abundant ligand-bound Mn(III), including porewaters, estuaries, and coastal waters, may be facilitated in part by abiotic reactions with Mn, even under functionally anoxic conditions.

The paper presents the first data on the nitrogen isotope composition of the associated gases of mineral waters in the North Caucasus and newly acquired data on the carbon isotope composition of the CO2 and CH4. Most of the samples were taken from the high- $${{p}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}$$ waters of the Elbrus and Kazbek volcanic areas in the Greater Caucasus. It is shown that δ15N changes in the range of –3.9 to +5.6‰ and synchronously increases in gases of the Caucasus Spa Area (CSA) with an increase in the N2 and CH4 concentrations. This correlation points to a genetic association of non-atmogenic nitrogen with sedimentary methane-generating processes. The values of δ13С in carbon dioxide in the Elbrus area vary from –11.8 to –3.0‰. The mean value of δ13С (СО2) tends to increase north of Elbrus volcano, and this trend may be a consequence of the increasing content of СО2 produced by the thermal decomposition of sedimentary carbonates in the composition of gases, as well as a result of low-temperature interaction of the high- $${{p}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}$$ waters with the Jurassic and Cretaceous carbonate rocks. It is shown that high- $${{p}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}$$ waters associated with Elbrus volcano often contain up to 12.4% CH4. This methane is characterized by high δ13С of –32.0 to –17.2‰. Analysis of the distribution of concentrations and δ13С values of СН4 around Elbrus and the presence of N2 with positive δ15N values in the gases suggest a crustal genesis of the methane. The role of magmatic activity in this situation is reduced to producing a temperature anomaly that activates carbon isotope exchange in the CO2–CH4 system.

Biochar has strong potential to improve nitrogen (N) use efficiency in both agricultural and horticultural systems. Biochar is usually co-applied with full rates of fertiliser. However, the extent to which N cycling can be affected after biochar application to meet plant N requirement remains uncertain. This study aimed to explore N cycling up to 2 years after biochar application. We applied pine woodchip biochar at 0, 10 and 30 t ha−1 (B0, B10, B30, respectively) in a macadamia orchard and evaluated the N isotope composition (δ15N) of soil, microbial biomass and macadamia leaves. Soil total N (TN) and inorganic N pools were also measured up to 2 years after biochar application. Biochar did not alter soil TN but soil NO3−-N increased at months 12 and 24 after biochar application. Soil NO3−-N concentrations were always over ideal levels of 15 μg g−1 in B30 throughout the study. Stepwise regression indicated that foliar δ15N decreases after biochar application were explained by increased NO3−-N concentrations in B30. Foliar TN and photosynthesis were not affected by biochar application. The soil in the high rate biochar plots had excess NO3−-N concentrations (over 30 μg g−1) from month 20 onwards. Therefore, N fertiliser applications could be adjusted to prevent excessive N inputs and increase farm profitability.

Nitrogen isotope fractionations between nitrogen oxides (NO and NO2 ) play a significant role in determining the nitrogen isotopic compositions ( δ15N ) of atmospheric reactive nitrogen. Both the equilibrium isotopic exchange between NO and NO2 molecules and the isotope effects occurring during the NOx photochemical cycle are important, but both are not well constrained. The nighttime and daytime isotopic fractionations between NO and NO2 in an atmospheric simulation chamber at atmospherically relevant NOx levels were measured. Then, the impact of NOx level and NO2 photolysis rate on the combined isotopic fractionation (equilibrium isotopic exchange and photochemical cycle) between NO and NO2 was calculated. It was found that the isotope effects occurring during the NOx photochemical cycle can be described using a single fractionation factor, designated the Leighton cycle isotope effect (LCIE). The results showed that at room temperature, the fractionation factor of nitrogen isotopic exchange is 1.0289±0.0019 , and the fractionation factor of LCIE (when O3 solely controls the oxidation from NO to NO2 ) is 0.990±0.005 . The measured LCIE factor showed good agreement with previous field measurements, suggesting that it could be applied in an ambient environment, although future work is needed to assess the isotopic fractionation factors of NO + RO 2 / HO 2 → NO 2 . The results were used to model the NO– NO2 isotopic fractionations under several NOx conditions. The model suggested that isotopic exchange was the dominant factor when NOx>20 nmol mol −1 , while LCIE was more important at low NOx concentrations ( nmol mol −1 ) and high rates of NO2 photolysis. These findings provided a useful tool to quantify the isotopic fractionations between tropospheric NO and NO2 , which can be applied in future field observations and atmospheric chemistry models.

The ability to accurately analyze nitrogen (N) isotopes of coal is important for evaluating its contribution to NOX emissions to the atmosphere via coal combustion. Although an elemental analyzer/isotope ratio mass spectrometer is highly efficient for analyzing the N isotopes of coal, it requires large amounts of organic matter (>3 mg) to produce enough N2 to enable N isotope measurements due to the high organic carbon contents of coal with relatively low N contents. Therefore, to completely oxidize the organic matter, more oxidant matter is required to enhance coal combustion in a reactor tube in an elemental analyzer through injecting O2 during the combustion process. One reference material (RM) (GBW11104) was used to determine the effect of amounts of O2 on the accuracy of nitrogen isotope values obtained. Our results show that small amounts of O2 injected into the EA resulted in incomplete coal combustion, which yielded a lower N content and more positive N isotope ratio for RM (GBW11104) than those obtained by complete combustion. Thus, to ensure the complete combustion of coal, large O2 injection amounts are required. The refined method was applied to provide the N isotope values of coals imported from Southeast Asia, Russia, and Australia. Combined with the carbon isotope values, the imported coals from three coal-producing regions (Southeast Asia, Russia, and Australia) display distinct characteristics.

The open ocean nitrogen cycle is being altered by increases in anthropogenic atmospheric nitrogen deposition and climate change. How the nitrogen cycle responds will determine long-term trends in net primary production (NPP) in the nitrogen-limited low latitude ocean, but is poorly constrained by uncertainty in how the source-sink balance will evolve. Here we show that intensifying nitrogen limitation of phytoplankton, associated with near-term reductions in NPP, causes detectable declines in nitrogen isotopes (δ15N) and constitutes the primary perturbation of the 21st century nitrogen cycle. Model experiments show that ~75% of the low latitude twilight zone develops anomalously low δ15N by 2060, predominantly due to the effects of climate change that alter ocean circulation, with implications for the nitrogen source-sink balance. Our results highlight that δ15N changes in the low latitude twilight zone may provide a useful constraint on emerging changes to nitrogen limitation and NPP over the 21st century., Projected declines in marine primary production are underpinned by a slowdown in nitrogen supplied to surface waters. Here the authors detail a new means to detect this slowdown and describe major shifts in the 21st century oceanic nitrogen cycle.

Natural gases in China are mainly coal-derived gas, with assistance from oil-typed gas. At present, many genetic identification methods, from hydrocarbon composition and isotope to light hydrocarbon and biomarker indexes, have been formed, but combined methods from non-hydrocarbon gases are lacking. Based on compositions and isotopes geochemical characteristics and the differences of non-hydrocarbon nitrogen gas in coal-derived gas and oil-typed gas, and combining the isotopic geochemical characteristics of non-hydrocarbon helium, the comprehensive identification methods of coal-derived gas and oil-typed gas for hydrocarbon gases according to the associated non-hydrocarbon gases of nitrogen and helium are established and the preliminary applications have been engaged. The main recognitions are as follows:1)Coal-derived gas generally has relatively lower nitrogen abundance, mainly distributed from 0 to 31.2% with main frequency from 0 to 2%. Oil-typed gas, on the other hand, usually has relatively higher nitrogen abundance, mainly distributed from 1.1 to 57.1% with main frequency from 2 to 16%. 2) Coal-derived gas generally has relatively heavier nitrogen isotope values, mainly distributed from -8 to 19.3‰ with main frequency from -8 to 8‰.Oil-typed gas usually has relatively lower nitrogen isotope values, mainly distributed from -10.6 to 4.6‰ with main frequency from -8 to 4‰.3)The geochemical characteristic differences of coal-derived gas and oil-typed gas are mainly due to the fact that the sapropel parent material is relatively rich in nitrogen element and rich in light δ14N, while the humic parent material is relatively poor in nitrogen element and rich in heavy δ15N. The differences on thermal maturity of source rocks, the redox conditions of source rock sedimentary environment, and the salinity of water body are also important effective factors.4)Differences on nitrogen abundances and isotopes in coal-derived gas and oil-typed gas have great significance in genetic identification. The genetic identification chart of R/Ra-δ15N for organic and inorganic nitrogen in natural gas and the comprehensive joint identification charts of R/Ra-δ15N-N2 of nitrogen and helium for coal-derived gas and oil-typed gas have been established, and are of great reference in investigating the origins and sources of natural gas and guiding natural gas exploration in China.

Exotic plant invasion is an urgent issue occurring in the biosphere, which can be stimulated by environmental nitrogen (N) loading. However, the allocation and assimilation of soil N sources between leaves and roots remain unclear for plants in invaded ecosystems, which hampers the understanding of mechanisms behind the expansion of invasive plants and the co-existence of native plants. This work established a new framework to use N concentrations and isotopes of soils, roots, and leaves to quantitatively decipher intra-plant N allocation and assimilation among plant species under no invasion and under the invasion of Chromolaena odorata and Ageratina adenophora in a tropical ecosystem of SW China. We found that the assimilation of N derived from both soil ammonium (NH4+) and nitrate (NO3-) were higher in leaves than in roots for invasive plants, leading to higher leaf N levels than native plants. Compared with the same species under no invasion, most native plants under invasion showed higher N concentrations and NH4+ assimilations in both leaves and roots, and increases in leaf N were higher than in root N for native plants under invasion. These results inform that preferential N allocation, dominated by NH4+-derived N, to leaves over roots as an important N-use strategy for plant invasion and co-existence in the studied tropical ecosystem.

The Ediacaran-Cambrian transition is marked by the diversification of metazoans. However, this is not true for the Bambuí Group, South-East Brazil, in which, despite its age, is almost fossil-barren. The reasons for such inhospitable conditions for the development of complex life forms in this progressively restricted foreland basin in the core of the West Gondwana continent are still being investigated. Thus, to enhance the comprehension of environmental conditions during the deposition of this basin, this work brings \'delta POT.15\'Nbulk data from rocks of its two lowermost 2nd-order sequences. Stable nitrogen isotopes are the only tool that allows the rebuilding of past N-cycles, and not only this is element is an essential part of life, they are a useful proxy to investigate the redox structure of the water column as the stability of N species are conditioned by the availability of oxygen in the environment. Here, a positive \'delta POT.15\'N excursion in the first transgressive system tract of the basin is reported, suggesting that the Bambuí basin was still connected to the global ocean. This excursion is interpreted as an event of increasing oxygenation of the Bambuí sea, as the increment of \'delta POT.15\'N values indicates that the dominant path of the N-cycle went from N2 direct fixation to NO3- assimilation. At the Early Highstand System Tract \'delta POT.15\'N values show that the nitrate pool that was established during the transgression persisted, however, as the restriction of the basin progressed, nitrate became scarce and N2 fixation became the main form of acquisition of N by microorganisms. Finally, \'delta POT.15\'N data from the second 2nd-order sequence points again to the existence of a nitrate pool during this interval, however, not as big or stable as the one from the first transgression. Hence, the data show that during the deposition of the basal Bambuí Group rocks, N2 fixation and NO3- assimilation alternated as the dominant path of the N cycle. Importantly, the instability of the N-cycle and redox conditions plus the scarcity of nitrate, especially during the deposition of the late highstand system tract, might have affected the development of complex life forms. A transição Ediacarano-Cambriano é marcada pela diversificação dos metazoários. No entanto, isso não é observado nas rochas do Grupo Bambuí, no leste do Brasil, que, apesar da sua idade, possuem um pobre e escasso registro fossilífero. As razões que levaram este ambiente a ser impróprio para o florescimento de vidas complexas nesta bacia progressivamente restrita ainda estão sendo investigadas. Assim, para compreender melhor as condições ambientais durante a deposição do Grupo Bambuí, este trabalho traz dados obtidos nas duas primeiras sequências de 2ª ordem. Isótopos estáveis de nitrogênio são a única ferramenta que permite reconstruir ciclos do N em tempos passados. Este elemento é uma parte essencial da vida e seus isótopos são úteis para investigar a estrutura redox de uma coluna de água, já que a estabilidade das espécies de N são condicionadas pela disponibilidade de oxigênio no ambiente. Neste trabalho, é descrita uma excursão \'delta POT.15\'N positiva no primeiro trato de sistema transgressivo da bacia. Neste ponto, o mar que deu origem às rochas do Grupo Bambuí ainda estava conectado ao oceano e essa excursão pode ser interpretada como um evento de aumento da oxigenação do mar, pois o aumento dos valores de \'delta POT.15\'N indica que a etapa dominante do ciclo do N foi da fixação direta do N2 para assimilação do NO3-. Já no início do trato de mar alto, os dados de \'delta POT.15\'N mostram que o reservatório de nitrato que se estabeleceu durante a transgressão persistiu, entretanto, conforme a restrição da bacia progrediu, o nitrato tornou-se escasso e a fixação de N2 passou a ser o mecanismo dominante de aquisição de N pelos microrganismos. Por fim, os dados de \'delta POT.15N\' da segunda sequência de 2ª ordem apontam novamente para a existência de um reservatório de nitrato durante este intervalo, porém não tão grande ou estável quanto o da primeira transgressão. Logo, os dados de \'delta POT.15\'N mostram que durante a deposição das unidades basais do Grupo Bambuí, a fixação de N2 e a assimilação de NO3- alternaram-se como o mecanismo dominante do ciclo de N. É importante ressaltar que a instabilidade do ciclo do nitrogênio, das condições redox e a escassez de nitrato, especialmente durante a deposição do trato de mar alto tardio, podem ter afetado o desenvolvimento de formas de vida complexas.

BACKGROUND: The nitrogen isotope ratio (NIR) is a promising index of traditional food intake for an Alaska Native (Yup'ik) population, which can be measured in blood and hair. However, the NIR has not been calibrated to high-quality measures of Yup'ik traditional food intake. OBJECTIVES: Our primary objective was to examine associations between intakes of Yup'ik traditional food groups, including fish, marine mammals, birds, land mammals, berries, greens, and total traditional foods, and the NIR. In an exploratory analysis, we also examined whether NIR analyzed sequentially along hair could reflect dietary seasonality. METHODS: We recruited 68 participants from 2 Yup'ik communities in the Yukon Kuskokwim region of Southwest Alaska (49% female, aged 14–79 y). Participants completed 4 unscheduled 24-h food recalls over the period peak of RBC and hair synthesis preceding a specimen collection visit. The NIR was measured in RBCs ( n = 68), a proximal hair section (n = 58), and sequential segments of hair from individuals in the upper 2 quartiles of traditional food intake having hair >6 cm in length, plus 2 low subsistence participants for reference (n = 18). Diet–biomarker associations were assessed using Pearson's correlation and linear regression. RESULTS: Intakes of fish, marine mammals, berries, and greens were significantly associated with the NIR. The strongest dietary association was with total traditional food intake (R(2) = 0.62), which indicated that each 1‰ increase in the RBC NIR corresponded to 8% of energy from traditional foods. Hair NIR appeared to fluctuate seasonally in some individuals, peaking in the summertime. CONCLUSIONS: Findings support the use of the RBC and hair NIR to assess total traditional food intake in a Yup'ik population. Analyses of sequential hair NIR provided evidence of seasonality in traditional food intake, although seasonal variations were modest relative to interindividual variation.

Identification of nitrate sources and its transformations are important for the management of large lakes and reservoirs. The Three Gorges Reservoir (TGR) in China is one of the largest reservoirs around the world. In this study, stable isotopes of nitrogen (δ15N–NO3−) and oxygen (δ18O–NO3−) of nitrate in water were used to gain insights into nitrate sources and transformations in the tail area of the TGR. Bayesian mixing model has been conducted to estimate the proportional contribute of nitrate sources. The mixing modelling results indicated that NH4+ fertilizer (range 7–54%) and soil organic nitrogen (range 2–45%) were the dominant NO3−–N sources in the tail area of the TGR during the three season study period. Nitrification contributed a part of NO3−–N in the river water during the dry season. The nitrate from soil solution in the riparian zone with denitrified NO3− might be another major reason for the enrichment of δ15N–NO3− and δ18O–NO3− during the normal season. Reducing the use of chemical nitrogen fertilizers, especially NH4+ fertilizers, and protecting soil from erosion may be effective measures to improve water quality in the TGR.

Due to the local emissions and transportations of air pollution from the most polluted regions such as the North China Plain and Yangtze Delta metropolitan, Xuzhou is becoming one of the most polluted cities in East China. The sources and formation processes of nitrogen-containing aerosols are therefore very complex. Two continuous aerosol measurement campaigns were conducted in this industrial city during the wintertime and summertime of 2016, to investigate the chemical compositions and potential sources of total nitrogen (TN, including 89% inorganic nitrogen and 11% organic nitrogen) in PM2.5. Abrupt enhancements of nitrogen-containing aerosols (e.g., NO3− and NH4+) were found in the winter, and nitrate became as a dominant contributor in high pollution days (e.g., PM2.5 > 150 μg m−3). Nitrogen oxidation ratios (NOR) correlated significantly with aerosol liquid water content (ALWC), which was estimated by ISORPROPIA-II model. This suggested heterogeneous process might be an important pathway in nitrate formation during the high PM2.5 days. The nitrogen isotope composition (δ15N) in TN varied from −1.3 to +13.2‰ with a mean value of 6.9 ± 3.6‰ during the wintertime. An isotope-based source apportionment approach was then developed using a Bayesian isotope mixing model (SIAR) with chemical compositions as an important constrain, which improved accuracy and reduced the overall uncertainties in estimations of TN sources. From this optimized model, we identified six major sources including NH3 from combustion-related emissions (49%), NH3 derived from animal wastes (6%), NH3 from urban volatilization (3%), NOx derived from coal combustion (33%), NOx from biomass burning (5%) and NOx from vehicles (3%). Our results demonstrated that ambient NOx was dominated by coal combustion. Since NOx and NH3 are important precursors for ammonium nitrate aerosols, controlling of combustion related NOx and NH3 emissions might be an important way to reduce PM2.5 levels in this region.

24 pages; International audience; The Earth’s oxygenation represents one of the most important environmental drivers of life’s evolution, with the first rise, known as ‘the Great Oxidation Event’ (GOE), corresponding to unpreceded accumulation of atmospheric O2, changes in the flux of marine nutrients and possibly global glaciations. However, the detailed evolution of the GOE is still debated, as for instance the accumulation trends of oceanic versus atmospheric oxygen and the nature of biogeochemical responses to oxygenation. Here, we combine organic carbon and bulk nitrogen isotope compositions with major element concentrations and iron speciation data of sedimentary rocks recovered from two drill cores (T2 and T3) in the early Paleoproterozoic Turee Creek Group, Western Australia, to track the redox evolution of marine conditions during the GOE. T2 core samples of the Kungarra Formation, which consists of clastic sedimentary rocks overlaid by the glaciogenic Meteorite Bore Member, were deposited ∼2.31 Ga ago. T3 core intercepts, from bottom to top, quartzite of the Koolbye Formation, and shales and stromatolitic carbonates of the Kazput Formation, which were deposited around ∼2.25 Ga. Samples from T2 show minor variations of δ13Corg (avg. −34.5 ± 1.7‰, n = 30), with no significant difference between siliciclastic and glaciogenic sedimentary rocks. In contrast, T3 samples display an increase in δ13Corg from −32.0 to −24.8‰ (n = 54) from shales to carbonates. In both T2 and T3 cores, δ13Corg values are inversely correlated with Al2O3, suggesting a strong petrological control on δ13Corg values, inferred here as resulting from variable contributions of detrital organic matter. Bulk N contents are low, from 13.5 to 56.7 ppm and 15.7 to 53.4 ppm in T2 and T3 samples, respectively. The δ15N values show a bimodal distribution, with one mode at +2.6‰ in T2 and another at +8.8‰ in T3, independent from lithological variations. This δ15N values shift between T2 and T3 is interpreted as reflecting a change from dominating N2-fixers to NO3-assimilating organisms. This implies an increase of NO3− availability, and thus of O2 concentration, during the time interval separating the deposition of T2 and T3 sediments. Dissolved NO3− and O2 concentrations of the Turee Creek marine basin are estimated from two models using N isotope data. The dissolved NO3− concentration has an upper limit ranging from 1.91 to 3.04 µM, about one order of magnitude below the average value of modern oceans. The lower limit for dissolved oxygen concentration ranges from 1.8 to 4.4 µM, which is two orders of magnitude lower than modern oceans. Together with previous studies, the present data place quantitative constraints on the redox changes associated with the Great Oxidation Event and illustrate a stepwise increase of NO3− bioavailability between 2.31 to 2.25 Ga, in relation with increasing O2 level.

The nitrogen stable isotope ratios of NH3 gas (δ15N-NH3(g)) and particulate NH4+ (δ15N-NH4+(p)) have been used to determine the sources and elucidate the environmental dynamics of NH3(g) and NH4+(p). Some studies have determined the sources from δ15N-NH4+(p) in the ambient environment by using the nitrogen isotope fractionation value (Δδ15N). Studies of Δδ15N are limited and estimated the Δδ15N by theoretical calculation or laboratory experiments in closed systems. Here, we produced actual submicron-sized particles and exposed them to NH3(g) in a dynamic chamber under various experimental conditions of temperature and NH3(g) turnover rate. Δδ15N was lower when temperature was higher. For low turnover rates (about 0.9 per day), the Δδ15N was 31.6 ± 2.0‰ (mean ± 1SD), almost equal to the Δδ15N from theoretical calculations and laboratory tests in closed systems. Also, the relationship between Δδ15N, the temperature, and the turnover rate can be described in the equation form. This relationship can help to explain the discrepancies between Δδ15N values in closed and open systems. Our results could help to clarify the sources and mechanisms of particle formation.

Trophic positions (TPs) are key parameters for determining trophic magnification factors (TMFs) of environmental pollutants. We used compound-specific nitrogen isotope analysis of amino acids (CSIA-AA), with which we expected to obtain precise TPs, to estimate the TMFs of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the pelagic and benthic food webs of Tokyo Bay. The objective of the present study was to evaluate the difference between TMFs derived from TPs estimated by CSIA-AA (TPGlu/Phe) and TMFs derived from TPs estimated by bulk stable isotope analysis (TPbulk). TPGlu/Phe tended to be lower than TPbulk for many pelagic and benthic fishes. In the pelagic food web, the slopes for the relationships between PCB concentrations and TPGlu/Phe exceeded those between PCB concentrations and TPbulk for many congeners in samples from December 2014, and TMFGlu/Phe values (0.89–6.9) were higher than TMFbulk values (0.92–3.8). However, there were no statistically significant differences between the slopes of the relationships between PCB and PBDE concentrations and TPbulk or TPGlu/Phe for any of the congeners (analysis of covariance, P ≥ 0.08). In the benthic food web, PCB concentrations correlated with TPGlu/Phe for 9 PCB congeners in the samples collected during December 2014, although the concentrations of none of the PCB congeners correlated with TPbulk. A decrease of TMFGlu/Phe and TMFbulk values from December 2014 to May 2015 suggested that variation of PCB and PBDE concentrations in the organisms had more effect than TPs on the TMFs.

Rationale Foodcrust, the charred deposit adhering to the surface of containers, is a possible source of information on the function of ancient vessels and the subsistence of prehistoric humans. While the carbon isotope ratios in those materials are useful in detecting the usage of C4 plants, the reliability of nitrogen isotopic signatures has not been fully investigated. Methods The validity of bulk nitrogen isotope ratios has previously been investigated in coastal or riverine environments, where multiple resources from terrestrial and aquatic ecosystems were available, but not in terrestrial settings which provide a simpler mixing of terrestrial animals and plants. Hence, we conducted an exhaustive study on charred deposits on potsherds at two inland archaeological sites belonging to prehistoric Jomon hunter-gathers in central Japan, focusing on δ15 N values and atomic N/C ratios determined using an isotope ratio mass spectrometer and an elemental analyzer, respectively. Results For both sites, the δ15 N values showed significant correlations with the N/C ratios among samples from the inner surface, suggesting that these have recorded animal contribution. Furthermore, previous studies of Neolithic pottery from North Europe and Far East Russia bearing strong marine signatures had shown reasonably higher δ15 N values and N/C ratios in comparison with our data from terrestrial settings. On the other hand, some charred materials probably originating from plant starch showed lower values with both parameters. Samples from the outer surface produced less meaningful isotopic and elemental ratios altered by a thermal effect and/or contamination from soot. Conclusions When the samples of foodcrusts were selected carefully from the inner surface, bulk nitrogen isotopes and N/C ratios reflect the composition of what was cooked or processed in containers. This will provide useful information for understanding the human adaptation from the Late Pleistocene to the Holocene in conjunction with residual lipid analyses.

Nitrate (NO3−) is a key component of secondary inorganic aerosols and PM2.5. However, the contributions of nitrogen oxides (NOx) emission sources to NO3− in PM2.5 remain poorly constrained. This study measured nitrogen (N) isotopes of NO3− (hereafter as δ15N-NO3-) in PM2.5 collected at Beijing in 2014. We observed that δ15N-NO3- values in PM2.5 (−2.3‰ − 19.7‰; 7.3 ± 5.4‰ annually) were significantly higher in winter (11.9 ± 4.4‰) than in summer (2.2 ± 2.5‰). The δ15N differences between source NOx and NO3− in PM2.5 (hereafter as Δ values) were estimated by a computation module as 7.8 ± 2.2‰ − 10.4 ± 1.6‰ (8.8 ± 2.4‰). Using the Δ values and δ15N values of NOx from major fossil (coal combustion, vehicle exhausts) and non-fossil sources (biomass burning, microbial N cycle), contributions of major NOx sources to NO3− in PM2.5 were further estimated by the SIAR model. We found that seasonal variations of δ15N-NO3- values in PM2.5 of Beijing were mainly caused by those of NOx contributions from coal combustion (38 ± 10% in winter, 20 ± 9% in summer). Annually, NOx from coal combustion, vehicle exhausts, biomass burning, and microbial N cycle contributed 28 ± 12%, 29 ± 17%, 27 ± 15%, and 16 ± 7% to NO3− in PM2.5, respectively, showing actually comparable contributions between non-fossil NOx (43 ± 16%) and fossil NOx (57 ± 21%). These results are useful for planning the reduction of NOx emissions in city environments and for elucidating relationships between regional NOx emissions and atmospheric NO3− pollution or deposition.

Fermentation is seldom considered in paleodietary analyses of Arctic and Subarctic peoples despite its ubiquitous traditional use as a cooking technique in high latitudes. Further, chemists have yet to assess the potential isotopic effects of fermentation on animal tissues, though isotopic research has documented measurable isotopic effects associated with other cooking techniques such as stewing and boiling. To measure the effects of fermentation on stable carbon and nitrogen isotopes, muscle tissues from 11 central Alaskan Chinook salmon (Oncorhynchus tshawytscha) were fermented following ethnographic methods. The results of this experiment demonstrate statistically significant isotopic differences in both carbon (−1.5‰) and nitrogen (+1.3‰) values taken from fermented muscle tissues compared to raw muscle tissues. Additionally, this study found a significant physiological fractionation effect between bone collagen and raw muscle (+3.3‰) consistent with previous research on Pacific salmon. In contrast to previous research, however, these tissues' nitrogen values show no significant fractionation. These findings have implications for central Alaskan dietary reconstructions, residue analyses, and our understanding of past subsistence practices in the Arctic and Subarctic.

Nitrification of the environment has resulted from tremendous increases in the use of fertilizers for crop plants. This has increased runoff to coastal marine areas with consequences for primary production, benthos and upper trophic-level consumers, including sea ducks such as eiders Somateria mollissima. This species primarily relies on filter-feeding bivalves, especially blue mussels Mytilus edulis. Stable isotopes of nitrogen (measured as δ15N) are incorporated in the feathers of eiders during molt at a constant rate reflecting the amount in food eaten. We examined if δ15N values in feathers can link eiders to the nitrogen loads in the marine waters surrounding Denmark, which is the main wintering grounds for the Baltic/Wadden Sea eider population. We also assessed how the abundance of eiders is related to nutrients and dead zones with oxygen deficit. During 2014–2018 we collected samples from 489 eiders, and of these 100 were analyzed for stable isotopes δ15N. Eider feather δ15N was positively related to nitrogen abundance in marine waters. Local aggregations of eiders in late summer (the molting period) and in winter increased with the amount of nitrogen in the marine environment. Large eiders took longer to molt, they molted later and the daily growth increments of feathers were larger. Finally, larger eiders and eiders in higher numbers occurred in areas with hypoxia. These findings show that anthropogenic inputs to the coastal marine environment positively influence the abundance and aggregations of eiders.

Most biological nitrogen transformations have characteristic kinetic isotope effects used to track these processes in modern and past environments. The isotopic fractionation associated with nitrogen fixation, the only biological source of fixed nitrogen (N), provides a particularly important constraint for studies of nitrogen cycling. Nitrogen fixation using the ‘canonical’ Mo-nitrogenase produces biomass with a δ^(15)N value of ca. −1‰ (vs. atmospheric N_2). If the ‘alternative’ V- and Fe-only nitrogenases are used, biomass δ^(15)N can be between −6‰ and −7‰. These biomass values are assumed to be relatively invariant and to reflect the cellular level expressed isotope effect of nitrogen fixation. However, field and laboratory studies report wide ranges of diazotrophic biomass δ^(15)N (from −3.6‰ to +0.5‰ for Mo-based nitrogen fixation). This variation could be partly explained by the release of dissolved organic N (DON) that is isotopically distinct from biomass. The model nitrogen fixer Azotobacter vinelandii secretes siderophores, small molecules that aid in Fe uptake and can comprise >30% of fixed nitrogen. To test whether siderophores (and other released N) can decouple biomass δ^(15)N from the isotope effect of nitrogen fixation we measured the isotopic composition of biomass and released N in Fe-limited A. vinelandii cultures fixing nitrogen with Mo- and V-nitrogenases. We report that biomass δ^(15)N was elevated under Fe limitation with a maximum value of +1.2‰ for Mo-based nitrogen fixation. Regardless of the nitrogenase isozyme used, released nitrogen δ^(15)N was also 2–3‰ lower than biomass δ^(15)N. Siderophore nitrogen was found to have a slightly higher δ^(15)N than the rest of the DON pool but was still produced in large enough concentrations to account for increases in biomass δ15N. The low δ^(15)N of siderophores (relative to biomass) is consistent with what is known from compound specific isotope studies of the amino acids used in siderophore biosynthesis, and indicates that other amino-acid derived siderophores should also have a low δ^(15)N. The implications for studies of nitrogen fixation are discussed.

Although groundwater nitrogen pollution has been widely studied, the control of hydrogeological conditions on behavior of nitrogen compounds has been poorly understood. In this study, multiple stable isotopes (N/C/H/O), spectral characteristics of DOM coupled with water chemistry were used to reveal the sources and fate of nitrate and ammonium in three subareas with different hydrogeological conditions in the Central Yangtze River Basin. We identified three contrasting patterns of nitrogen sources and fate in groundwater controlled by different aquifer features. In a reducing porous aquifer mainly composed of carbonate minerals overlain by a thick low-permeability layer, the NH4–N concentration is high (mean 4.12 mg/L) but with quite low NO3–N concentration (mean 0.28 mg/L). The high ammonium is mainly from intense degradation of organic matter (OM), while denitrification at a higher rate results in nitrate removal. Feammox may be favored owing to abundant humics acting as the electron shuttle. In a weakly reducing to oxidizing porous aquifer mainly composed of aluminosilicate minerals overlain by a varying thickness of low-permeability layer, high ammonium occurs in a weakly reducing condition and is affected by both anthropogenic input and OM degradation, while high nitrate occurs in a more oxidizing condition and could be mainly from soil nitrogen, manure or sewage. Feammox may be also favored due to more acidic environment formed by weathering of aluminosilicate minerals, fluctuating redox condition and low abundance of labile organic carbon, while denitrification occurs at a slower rate coupled with concurrent re-oxidation of nitrite to nitrate. In an oxidizing porous - fissured aquifer system overlain by a thin low-permeability layer, the concentrations of ammonium and nitrate are both low, possibly due to strong hydrodynamic and flushing condition, although slightly higher concentration of nitrate exhibit similar sources and fate with the weakly reducing to oxidizing porous aquifer mentioned above.

Large rivers are important terrestrial dissolved organic matter (DOM) sources to marginal seas, and dissolved organic nitrogen (DON) plays an essential role in DOM cycling. The Yellow River ranks as the fifth largest river (in length) in the world and is well-known for its high dissolved inorganic nitrogen (DIN) concentration and relatively low DON concentration, leading to extreme measuring uncertainties in DON and nitrogen isotopic composition (δ15N), consequently leaving its DON cycling as an unresolved puzzle. To fill such a knowledge gap, we analyzed 17 samples from the middle to downstream with a combination of spectroscopy, tangential flow filtration, nitrogen isotope, and DNA sequencing. DON

Understanding of nitrogen stable isotope variation in maize hybrids might help obtaining information on nitrogen absorption and distribution in different maize hybrids. In this study, we examined the nitrogen isotopic composition of different parts of maize hybrids under a laboratory culture experiment. The results showed that the δ15N values of different parts of the maize hybrid and its parents were ordered as follows: δ15Nstem>δ15Nleaf>δ15Nroot. The variation pattern of δ15N between the roots and leaves(Δδ15Nroot-leaf) of the maize hybrid was the same as that of δ15N between the roots and stems (Δδ15Nroot-stem). Therefore, the order of Δδ15Nroot-leaf as well as Δδ15Nroot-stem was as follows: Δδ15Nroot-leaf of the maize hybrid>Δδ15Nroot-leaf of the female parent (T4)>Δδ15Nroot-leaf of the male parent (803) and Δδ15Nroot-stem of the maize hybrid>Δδ15Nroot-stem of the female parent (T4)>Δδ15Nroot-stem of the male parent (803). This order is consistent with heterosis, indicating that differences in δ15N reflect the phenomenon of heterosis. The present study provides data in support of using the isotope technique to determine nitrogen distributions inside a plant and guide crossbreeding.

Nitrate (NO3−) is one of the most important inorganic ions in fine particulate (PM2.5) and drives regional haze formation; however, the NO3− sources and formation mechanisms in different seasons and regions are still debated. Here, PM2.5 samples were collected from Kunming and Nanning in southwestern China from September 1, 2017, to February 28, 2018 (spanning warm and cold months). We measured the daily O and N isotopic compositions of NO3− (δ18O–NO3− and δ15N–NO3−), estimated the δ18O–HNO3 values produced by different oxidation pathways, and quantified the NO3− formation pathways based on the isotope mass-balance equation. Our results showed that the δ18O–NO3− values in Kunming (65.3 ± 7.6‰) and Nanning (67.7 ± 10.1‰) are close to the δ18O–HNO3 values arising from the OH radical pathway (POH, 54.7 ± 1.2‰ to 61.2 ± 1.8‰), suggesting that the δ18O–NO3− values are mainly influenced by POH, which showed a contribution greater than 74%. Stronger surface solar radiation and higher air temperatures in low-latitude regions and warm months increased the amount of HNO3 produced by POH and reduced the amount of HNO3 produced by PN2O5, which produced low δ18O–NO3− values. Increased air pollution emissions decreased the contribution from POH and increased the contribution from N2O5 and NO3 pathways (PN2O5+NO3). The δ15N–NO3− values of PM2.5 in Kunming (7.3 ± 2.8‰) were slightly higher than those in Nanning (2.8 ± 2.7‰). The increased NOx emissions with positive isotopic values led to high δ15N–NO3− values in northern China and during cold months. A higher fNO2 (fNO2 = NO2/(NO + NO2), temperature, and contribution of POH produced lower N isotope fractionation between NOx and δ15N–NO3−, which was found to further decrease the δ15N–NO3– values in southwestern China and during warm months.

Stable isotope analysis is an increasingly used molecular tool to reconstruct the diet and ecology of elusive primates such as unhabituated chimpanzees. The consumption of C4plant feeding termites by chimpanzees may partly explain the relatively high carbon isotope values reported for some chimpanzee communities. However, the modest availability of termite isotope data as well as the diversity and cryptic ecology of termites potentially consumed by chimpanzees obscures our ability to assess the plausibility of these termites as a C4resource. Here we report the carbon and nitrogen isotope values from 79Macrotermestermite samples from six savanna woodland chimpanzee research sites across equatorial Africa. Using mixing models, we estimated the proportion ofMacrotermesC4plant consumption across savanna woodland sites. Additionally, we tested for isotopic differences between termite colonies in different vegetation types and between the social castes within the same colony in a subset of 47 samples from 12 mounds. We found thatMacrotermescarbon isotope values were indistinguishable from those of C3plants. Only 5 to 15% ofMacrotermesdiets were comprised of C4plants across sites, suggesting that they cannot be considered a C4food resource substantially influencing the isotope signatures of consumers. In theMacrotermessubsample, vegetation type and caste were significantly correlated with termite carbon values, but not with nitrogen isotope values. LargeMacrotermessoldiers, preferentially consumed by chimpanzees, had comparably low carbon isotope values relative to other termite castes. We conclude thatMacrotermesconsumption is unlikely to result in high carbon isotope values in either extant chimpanzees or fossil hominins.

Remediation of nitrate pollution of Earth’s rivers and aquifers is hampered by cumulative biogeochemical processes and nitrogen sources. Isotopes (δ15N, δ18O) help unravel spatiotemporal nitrogen(N)-cycling of aquatic nitrate (NO3−). We synthesized nitrate isotope data (n = ~5200) for global rivers and shallow aquifers for common patterns and processes. Rivers had lower median NO3− (0.3 ± 0.2 mg L−1, n = 2902) compared to aquifers (5.5 ± 5.1 mg L−1, n = 2291) and slightly lower δ15N values (+7.1 ± 3.8‰, n = 2902 vs +7.7 ± 4.5‰, n = 2291), but were indistinguishable in δ18O (+2.3 ± 6.2‰, n = 2790 vs +2.3 ± 5.4‰, n = 2235). The isotope composition of NO3− was correlated with water temperature revealing enhanced N-cascading in warmer climates. Seasonal analyses revealed higher δ15N and δ18O values in wintertime, suggesting waste-related N-source signals are better preserved in the cold seasons. Isotopic assays of nitrate biogeochemical transformations are key to understanding nitrate pollution and to inform beneficial agricultural and land management strategies.

Roaldite (Fe4N) is one of the few nitride minerals found in meteorites. Their nitrogen (N) isotopic signatures carry important information for understanding the early N cycle in the proto-solar nebula. However, the lack of knowledge on the N isotopic effects from nitride formation to its survival from frictional heating during landing impedes the interpretation and application of N isotope compositions of nitride minerals in meteorites. Here, we carried out laboratory experiments under a recently proposed roaldite forming condition, i.e., NH3 (as starting N source) reacting with metallic Fe at medium temperatures. We observed Fe4N formation over a large range of temperatures from 300�����C to 700�����C. The formation of Fe4N was associated with equilibrium N isotope fractionations with ��Fe4N-NH3 values of 0.9907 (��0.0004) at 300�����C and 0.9936 (��0.0004) at 500�����C, respectively. In the experimental pressure conditions (initial PNH3���=���3.9���6.4���bar, PTotal���300���. Thus, great caution is needed when using N isotope composition of roaldite (and probably other nitride minerals as well) to trace source information.

Information on the sources and transformations of particulate organic N (PN) and dissolved organic N (DON) at the coastal interface remains insufficient due to technological difficulties and complicated features of intensive physical mixing and rapid biological activities. Here, we investigated the spatial distribution of concentrations and isotopic compositions of PN and DON in the Changjiang plume during the summer flood period. In average, DON and PN accounted for 25.6 ± 12.1% and 8.1 ± 9.1% (n = 55), respectively, of the total N pool, with the remaining N primarily in the form of nitrate (NO3−). Mean δ15N values were the lowest for DON (−0.1 ± 2.7‰, n = 58) and slightly higher for PN (2.0 ± 1.6‰, n = 101), and the highest for NO3− (6.5 ± 2.2‰, n = 67), suggesting multiple transformations had occurred to differentiate isotopic characteristics among the three N pools. By applying a conservative mixing model, we found DON deficits (−3.5 ± 3.7 μmol L−1, n = 43) and negative shift in δ15NDON (−3.6 ± 2.2‰, n = 43) in the Changjiang plume, revealing nonconservative DON behaviors. In the offshore surface plume where Chlorophyll a was high, the most likely cause is the DON uptake by phytoplankton with a strong inverse isotope effect (around −40‰). This DON assimilation by phytoplankton contributed to ~16 ± 12% of the PN production, with the remaining supported by NO3− assimilation, producing an overall isotope effect of 4–9‰. However, in waters near the river mouth and at the bottom of the offshore plume where total suspended matter concentrations were high (>5 mg L−1), the DON deficit was most likely induced by the selective adsorption of 15N enriched moieties of DON onto particulate surfaces (with an isotope effect of −20‰ to −5‰). Unlike dissolved organic carbon to behave conservatively in most estuaries, our results show that active transformations had occurred between the DON and PN pools in the Changjiang plume.

The origin of ammonium-nitrogen in Indonesian coastal groundwater has not been intensively examined, meanwhile the elevated concentration remains a concern. This research aims at tracing the potential sources of ammonium-nitrogen in the groundwater of Indramayu, Indonesia where groundwater is vital for livelihood. From results, a combined examination of nitrogen isotope, coliform bacteria, land-use, and geology confirmed the natural and anthropogenic origins of ammonium-nitrogen in the groundwater. In the brackish-water aquaculture region, groundwater has &delta, 15NNH4 values from +1.8 to +4.8&permil, signifying that ammonium-nitrogen is derived from mineralization of organic nitrogen to ammonium. Furthermore, ammonium has a significantly positive relationship with sodium indicating the exchangeable ammonium is mobilized to groundwater via cation exchange. Meanwhile ammonium-nitrogen from anthropogenic waste was detected in agricultural and residential region. The groundwater has more varied &delta, 15NNH4 values, from &minus, 2.9 to +16.1&permil, which implies attenuation of ammonium-nitrogen from several sources namely manure, mineral fertilizer, sewage, and pit latrines. Also, the presence of E. coli confirms the indication of human and animal waste contamination. However, since ammonium has no relationship with sodium, cation exchange is not feasible and ammonium-nitrogen flows into the groundwater from anthropogenic sources along with liquid wastes.

In nature-based treatment systems, such as constructed wetlands, plant uptake of nutrients can be a significant removal pathway. Current methods for quantifying plant uptake of nitrogen in constructed wetlands, which often involve harvesting biomass and assuming that all nitrogen stored in plants was derived from wastewater, are inappropriate in pilot- and full-scale systems where other sources of nitrogen are available. To improve our understanding of nitrogen cycling in constructed wetlands, we developed a new method to quantify plant uptake of nitrogen by using stable isotopes and a mixing model to distinguish between nitrogen sources. We applied this new method to a pilot-scale horizontal levee system (i.e., a subsurface constructed wetland) over a two-year monitoring period, during which 14% of nitrogen in plants was wastewater-derived on average and the remaining plant nitrogen was obtained from the soil. Analysis of nitrogen isotopes indicated substantial spatial variability in the wetland: 82% of nitrogen in plants within the first 2m of the slope came from wastewater while less than 12% of plant nitrogen in the remainder of the wetland originated from wastewater. By combining these source contributions with remote-sensing derived total biomass measurements, we calculated that 150kgN (95% CI=50kgN, 330kgN) was taken up and retained by plants during the two-year monitoring period, which corresponded to approximately 8% of nitrogen removed in the wetland. Nitrogen uptake followed seasonal trends, increased as plants matured, and varied based on design parameters (e.g., plant types), suggesting that design decisions can impact this removal pathway. This new method can help inform efforts to understand nitrogen cycling and optimize the design of nature-based nutrient control systems.

We investigated the within- and between-leaf variability in the carbon and nitrogen isotope composition (δ 13 C and δ 15 N) and total nitrogen (TN) content in two grapevine cultivars (Vitis vinifera cv. Chasselas and Pinot noir) field-grown under rain-fed conditions. The within-leaf variability was studied in discs sampled from base-to-tip and left and right regions from the margin to midrib. The intra- and interplant variability was studied by comparing leaves at different positions along the shoot (basal, median, apical). In leaves from both cultivars, a decrease in δ 13 C from base to tip was observed, which is in line with an upward gradient of stomatal density and chlorophyll concentration. Less important, but still significant differences were observed between the right and left discs. The leaf TN and δ 15 N values differed between cultivars, showed smaller variations than the δ 13 C values, and no systematic spatial trends. The intraleaf variations in δ 13 C, δ 15 N, and TN suggest that stomatal behavior, CO 2 fixation, chlorophyll concentrations, and the chemical composition of leaf components were heterogeneous in the leaves. At the canopy scale, the apical leaves had less 13 C and more 15 N and TN than the basal leaves, indicating differences in their photosynthetic capacity and remobilizations from old, senescing leaves to younger leaves. Overall, this study demonstrates patchiness in the δ 13 C and δ 15 N values of grapevine leaves and species-specificity of the nitrogen assimilation and 15 N fractionation. These findings suggest that care must be taken not to overinterpret foliar δ 13 C and δ 15 N values in studies based on fragmented material as markers of physiological and biochemical responses to environmental factors.

Changes in leaf carbon and nitrogen isotope composition (δ 13 C and δ 15 N values) and the accumulation of epicuticular lipids have been associated with plant responses to water stress. We investigated their potential use as indicators of early plant water deficit in two grapevine (Vitis vinifera L.) cultivars, Chasselas and Pinot noir, that were field-grown under well-watered and water-deficient conditions. We tested the hypothesis that the bulk δ 13 C and δ 15 N values and the concentrations of epicuticular fatty acids may change in leaves of similar age with the soil water availability. For this purpose, leaves were sampled at the same position in the canopy at different times (phenological stages) during the 2014 growing season. Bulk dry matter of young leaves from flowering to veraison had higher δ 13 C values, higher total nitrogen content, and lower δ 15 N values than old leaves. In both cultivars, δ 15 N values were strongly correlated with plant water deficiency, demonstrating their integration of the plant water stress response. δ 13 C values recorded the water deficiency only in those plants that had not received foliar organic fertilization. The soil water deficiency triggered the accumulation of C >26 fatty acids in the cuticular waxes. The compound-specific isotope analysis (CSIA) of fatty acids from old leaves showed an increase in δ 13 C among the C 16 -C 22 chains, including stress signaling linoleic and linolenic acids. Our results provide evidence for leaf 13 C-enrichment, 15 N-depletion, and enhanced FA-chain elongation and epicuticular accumulation in the grapevine response to water stress. The leaf δ 13 C and δ 15 N values, and the concentration of epicuticular fatty acids can be used as reliable and sensitive indicators of plant water deficit even when the level of water stress is low to moderate. They could also be used, particularly the more cost-efficient δ 13 C and δ 15 N measurements, for periodic biogeochemical mapping of the plant water availability at the vineyard and regional scale.

Food choices affect the isotopic composition of the body with each food item leaving its distinct isotopic imprint. The common view is that the natural abundance of the stable isotopes of nitrogen (expressed as &delta, 15N) is higher in animals than in plants that constitute our contemporary diets. Higher &delta, 15N is thus increasingly viewed as a biomarker for meat and fish intake. Here we show that organic compared to conventional farming increases plant &delta, 15N to an extent that can appreciably impact the performance of &delta, 15N as a biomarker. The error that can arise when organic plants are consumed was modelled for the entire range of proportions of plant versus animal protein intake, and accounting for various intakes of organic and conventionally grown crops. This mass balance model allows the interpretation of differences in &delta, 15N in light of organic food consumption. Our approach shows that the relationship between &delta, 15N and meat and fish intake is highly contextual and susceptible to variation at the population, community or group level. We recommend that fertilization practices and organic plant consumption must not be overlooked when using &delta, 15N as a biomarker for meat and fish intake or to assess compliance to nutritional interventions.