Fractionation Of Nitrogen Stable Isotopes Research Articles

Isotope fractionation (δ13C, δ15N) and microbial community response in degradation of petroleum hydrocarbons by biostimulation in contaminated soil.

This study investigated the isotope effects of δ13C and δ15N and microbial response during biodegradation of hydrocarbons by biostimulation with nitrate or compost in the petroleum-contaminated soil. Compost and KNO3 amendments promoted the total petroleum hydrocarbon (TPH) removal accompanied by a significant increase of Actinobacteria and Firmicutes phyla. Soil alpha diversity decreased after 90 days of biostimulation. An inverse significant carbon isotope effect (εc = 16.6 ± 0.8‰) and strong significant nitrogen isotope effect (εN = -24.20 ± 9.54‰) were shown by the KNO3 supplementation. For compost amendment, significant carbon and nitrogen isotope effect were εc = 38.8 ± 1.1‰ and εN = -79.49 ± 16.41‰, respectively. A clear difference of the carbon and nitrogen stable isotope fractionation was evident by KNO3 or compost amendment, which indicated that the mechanisms of petroleum degradation by adding compost or KNO3 may be different.

Carbon, hydrogen and nitrogen stable isotope fractionation allow characterizing the reaction mechanisms of 1H-benzotriazole aqueous phototransformation

1H-benzotriazole is part of a larger family of benzotriazoles, which are widely used as lubricants, polymer stabilizers, corrosion inhibitors, and anti-icing fluid components. It is frequently detected in urban runoff, wastewater, and receiving aquatic environments. 1H-benzotriazole is typically resistant to biodegradation and hydrolysis, but can be transformed via direct photolysis and photoinduced mechanisms. In this study, the phototransformation mechanisms of 1H-benzotriazole were characterized using multi-element compound-specific isotope analysis (CSIA). The kinetics, transformation products, and isotope fractionation results altogether revealed that 1H-benzotriazole direct photolysis and indirect photolysis induced by OH radicals involved two alternative pathways. In indirect photolysis, aromatic hydroxylation dominated and was associated with small carbon (εC = -0.65 ± 0.03‰), moderate hydrogen (εH = -21.6‰), and negligible nitrogen isotope enrichment factors and led to hydroxylated forms of benzotriazole. In direct photolysis of 1H-benzotriazole, significant nitrogen (εN = -8.4 ± 0.4 to -4.2 ± 0.3‰) and carbon (εC = -4.3 ± 0.2 to -1.64 ± 0.04‰) isotope enrichment factors indicated an initial N-N bond cleavage followed by nitrogen elimination with a C-N bond cleavage. The results of this study highlight the potential for multi-element CSIA application to track 1H-benzotriazole degradation in aquatic environments.

Nitrogen isotope fractionation in a continuous culture system containing phytoplankton and blue mussels

An experiment was conducted to examine the fractionation of nitrogen stable isotopes in a continuous culture system containing field collected estuarine phytoplankton and blue mussels, Mytilus edulis. Nitrate and phosphate were added to culture vessels at concentrations above ambient levels and nitrogen isotope ratios (δ15N) were measured in particulate matter (PM) and blue mussels over the course of the 15-day experiment. The added nutrients resulted in large productivity and chlorophyll increases in the system. Study results indicate that rapid and significant nitrogen isotope fractionation can occur during incorporation by phytoplankton grown under conditions of excess dissolved inorganic nitrogen, as shown by δ15N values depleted by as much as 9‰ in PM from the higher nutrient treatments. These lower δ15N values were also reflected in mussels exposed to culture vessels effluents. Therefore, nitrogen concentration needs to be considered when using δ15N values in biota as indicators of anthropogenic nitrogen inputs.

Carbon and nitrogen stable isotope fractionation during abiotic hydrolysis of pesticides

Compound-specific Stable Isotope Analysis (CSIA) has been recently established as a tool to study pesticide degradation in the environment. Among degradative processes, hydrolysis is environmentally relevant as it can be chemically or enzymatically mediated. Here, CSIA was used to examine stable carbon and nitrogen isotope fractionation during abiotic hydrolysis of legacy or currently used pesticides (chloroacetanilide herbicides: Acetochlor, Alachlor, S-Metolachlor and Butachlor, acylalanine fungicide: Metalaxyl, and triazine herbicide: Atrazine). Degradation products analysis and CN dual-CSIA allowed to infer hydrolytic degradation pathways from carbon and nitrogen isotopic fractionation. Carbon isotopic fractionation for alkaline hydrolysis revealed similar apparent kinetic isotope effects (AKIEC = 1.03–1.07) for the 6 pesticides, which were consistent with SN2 type nucleophilic substitutions. Neither enantio-selectivity (EF ≈ 0.5) nor enantio-specific isotope fractionation occurred during hydrolysis of R (AKIEC = 1.04 ± 0.01) and S (AKIEC = 1.04 ± 0.02) enantiomers of a racemic mixture of Metalaxyl. Dual element isotope plots enabled to tease apart CCl bond breaking of alkane (Λ ≈ εN/εC ≈ 0, Acetochlor, Butachlor) and aromatic π-system (Λ ≈ 0.2, Atrazine) from CO bond breaking by dealkylation (Λ ≈ 0.9, Metalaxyl). Reference values for abiotic versus biotic SN2 reactions derived from carbon and nitrogen CSIA may be used to untangle pesticide degradation pathways and evaluate in situ degradation during natural and engineered remediation.

Solvent stress-induced changes in membrane fatty acid composition of denitrifying bacteria reduce the extent of nitrogen stable isotope fractionation during denitrification

Microcosm experiments with the well-studied denitrifier Thaurera aromatica show a link between a higher maximum membrane concentration (MMC) of the toxic organic solvents 1-octanol and 4-chlorophenol and a higher degree of saturation (DoS) of the fatty acids in the cell membrane. This coincides with less pronounced stable isotope fractionation during denitrification. We suggest that the change in cell membrane fluidity and the cell’s stress response leads to a decrease in nitrate transport across the cell membrane and/or an increase in the relative ratio of respiratory nitrate reduction rate versus efflux of unreacted nitrate. Both models show that the apparent kinetic isotope effect (AKIE) approach unity and thus reduce the extent of the resulting stable isotope enrichment factor ε15N-NO3− in dissolved nitrate during denitrification, as experimentally and mathematically shown in this study. This may lead to an underestimation of nitrate reduction determined by nitrate stable isotope analysis in aquatic habitats where various types of stresses may affect the physiology of the driving microorganisms.

Fractionation of stable nitrogen isotopes (<sup>15</sup>N/<sup>14</sup>N) during enzymatic deamination of glutamic acid: Implications for mass and energy transfers in the biosphere

Fractionation of stable nitrogen isotopes (<sup>15</sup>N/<sup>14</sup>N) during enzymatic deamination of glutamic acid: Implications for mass and energy transfers in the biosphere

Determination of the in situ growth rate of Microcystis based on carbon and nitrogen stable isotope fractionation

Abstract Stable isotope fractionation of carbon and nitrogen in algal cells can be affected by photosynthesis, temperature, nutrient and CO2 concentrations, and cell size. As a consequence, carbon and nitrogen stable isotope techniques are not popular for determining algal growth rates. To counter these issues, this study used BG11 medium to cultivate Microcystis in the laboratory. First, the carbon and nitrogen stable isotope values of the culture medium and the algae are determined. Then, based on changes in isotope fractionation before and after cell division, a function μ = 1.32(1 + x)−0.52 relating growth rate and stable isotope fractionation is established. By substituting stable isotope values from Taihu Lake water and Microcystis into this function, the growth rate of the Microcystis in Taihu Lake is calculated to be 0.64 d−1 in May and 0.12 d−1 in September, with an average growth rate of 0.42 d−1. By incorporating most of the above-mentioned factors influencing isotope fractionation, this method can determine the growth rate of algae based directly on the stable isotope fractionation relationship, enabling simple and practical determination of algae growth rates.

Enantioselective disturbance of chiral herbicide dichlorprop to nitrogen metabolism of Arabidopsis thaliana: Regular analysis and stable isotope attempt

As the most essential element, nitrogen play a pivotal role in plant physiological process, which is susceptible to contaminants. However, the enantioselective effects of chiral herbicides on nitrogen metabolism have not been comprehensively understood. In this study, effects of chiral herbicide dichlorprop (DCPP) on the nitrogen behaviors in Arabidopsis thaliana were investigated. The results revealed that the uptakes of inorganic nitrogen (NO3− and NH4+) were preferentially impacted by herbicidal active (R)-DCPP, where the transportation of beneficial NO3− was inhibited but the toxic NH4+ was accumulated. As for nitrogen assimilation, enantioselectivity was disappeared and reoccurred when NO3− was assimilated into NH4+. Furthermore, the pathways of NH4+ assimilation differed in Arabidopsis exposed to DCPP enantiomers, where (S)-DCPP remained almost the same to the control relying on GS-GOGAT cycle, but the dominant pathway in (R)-DCPP group was shifted to glutamate dehydrogenase route. Consequently, a profound enantioselectivity was also observed in the effects on amino acids synthesis. As for nitrogen stable isotope fractionation, (R)-DCPP led to more negative δ15N values than (S)-DCPP at 0.3μM, indicating the selective uptake of toxic NH4+ and different discrimination of δ15N was also observed between DCPP enantiomers. Moreover, stable isotopic evidence also revealed the disturbance caused by DCPP to the balance of nitrogen demand and consumption in A. thaliana. All these results may contribute to the final enantioselective toxicity, providing a new sight into the better understanding the action mechanism of chiral herbicides.

Nonlinear dynamic model describing the fractionation of stable nitrogen isotopes in denitrification process with nitrous oxide formation

Soil thawing in permafrost zones can lead to the formation of readily digestible organic matter. This intensifies nitrate denitrification processes, leading to the formation of nitrous oxide, which produces a considerable greenhouse effect, and its release into the atmosphere. Therefore, studying denitrification pro� cesses is an important problem at a planetary scale. A mathematical model is proposed, based on a modifica� tion of the classical Monod dependence for the rate of the process as a function the concentrations of two substrates—nitrate and organic matter—describing the fractionation dynamics of stable nitrogen isotopes 14 N and 15 N in the process of denitrification of nitrates ( ). The model was calibrated against experimen� tal data. The model gives a description of nonlinear fractionation dynamics at both excess and deficiency of digestible organic matter. The conventional Rayleigh equation, derived from firstorder kinetics with respect to the substrate (nitrate) and the nonlinear model yield similar results.

Carbon and nitrogen isotope fractionation of amino acids in an avian marine predator, the gentoo penguin (Pygoscelis papua).

Compound-specific stable isotope analysis (CSIA) of amino acids (AA) has rapidly become a powerful tool in studies of food web architecture, resource use, and biogeochemical cycling. However, applications to avian ecology have been limited because no controlled studies have examined the patterns in AA isotope fractionation in birds. We conducted a controlled CSIA feeding experiment on an avian species, the gentoo penguin (Pygoscelis papua), to examine patterns in individual AA carbon and nitrogen stable isotope fractionation between diet (D) and consumer (C) (Δ13CC-D and Δ15NC-D, respectively). We found that essential AA δ13C values and source AA δ15N values in feathers showed minimal trophic fractionation between diet and consumer, providing independent but complimentary archival proxies for primary producers and nitrogen sources respectively, at the base of food webs supporting penguins. Variations in nonessential AA Δ13CC-D values reflected differences in macromolecule sources used for biosynthesis (e.g., protein vs. lipids) and provided a metric to assess resource utilization. The avian-specific nitrogen trophic discrimination factor (TDFGlu-Phe = 3.5 ± 0.4‰) that we calculated from the difference in trophic fractionation (Δ15NC-D) of glutamic acid and phenylalanine was significantly lower than the conventional literature value of 7.6‰. Trophic positions of five species of wild penguins calculated using a multi-TDFGlu-Phe equation with the avian-specific TDFGlu-Phe value from our experiment provided estimates that were more ecologically realistic than estimates using a single TDFGlu-Phe of 7.6‰ from the previous literature. Our results provide a quantitative, mechanistic framework for the use of CSIA in nonlethal, archival feathers to study the movement and foraging ecology of avian consumers.

Describing a kinetic effect of fractionation of stable nitrogen isotopes in nitrification process

A mathematical model is proposed to assess the dynamics of stable nitrogen isotopes 14N and 15N in nitrification process—transformation of ammonium into nitrites and nitrates. The model was calibrated against experimental data with nitrite as an end nitrification product. The model, which use the Monod dependence, provides a description of the nonlinear dynamics of functioning and enables improving the kinetic coefficient of nitrification process.

Diet‐tissue fractionation of δ15N by consumers from streams and rivers

Variation in the diet‐tissue fractionation of stable nitrogen isotopes (Δ15N) is a major source of uncertainty in mixing model outputs and the calculation of trophic level in food web studies in aquatic systems. Using δ15N and δ13C of algae and consumers collected from a broad range of streams and rivers in Australia and New Guinea, we calculated Δ15N using a gradient approach, and compared these estimates with those from the literature. Riverine invertebrates and fishes from this region have δ15N diet‐tissue fractionation at the low end of the range of values reported for literature summaries, but different trophic groups had different Δ15N estimates. Source‐consumer regressions based on δ13C had lower slope estimates and lower R2 values compared with those based on δ15N. This implies that although consumers on average obtain a portion of their organic carbon from higher plants, they derive most of their organic nitrogen from N‐rich algae. Use of appropriate Δ15N for riverine consumers will lead to more satisfactory results with isotope mixing models, and the uncertainty associated with Δ15N estimates can be incorporated in the latest iterations of these models that are probabilistic rather than deterministic.

N:P ratios, δ 15N fractionation and nutrient resorption along a nitrogen to phosphorus limitation gradient in an oligotrophic wetland complex

The vegetation N:P ratio is thought to be a diagnostic indicator of the nature of nutrient limitation in wetland vegetation. It should therefore be closely linked to other indicators of nutrient acquisition and conservation, such as nitrogen stable isotope fractionation (δ 15N), nutrient resorption efficiency (RE) and resorption proficiency (RP). However, the interrelationships among these traits and the N:P ratio remain unclear. We compared tissue nutrient concentrations, N:P ratios, δ 15N fractionation, RE, and RP along an N to P limitation gradient in an oligotrophic wetland valley in the South Island of New Zealand. Within the valley, the soil TN:TP ratio increased from 1.3 to 18.0 in three discrete wetlands along the gradient. In pooled data from all vegetation communities within each site, the mass-based vegetation N:P ratio correlated significantly ( r 2 = 0.35, P < 0.01) to soil TN:TP ratios and increased from 10.2 ± 2.7 to 13.5 ± 3.6 along the N to P limitation gradient. This was accompanied by an increase in tissue δ 15N enrichment from 2.05 ± 1.12‰ to 6.27 ± 1.70‰, consistent with more open N cycling and lower N demand. These trends held within all vegetation types, but were particularly strong in a Typha orientalis (C-strategist) community (soil TN:TP vs vegetation N:P correlation r 2 = 0.78, P < 0.001; δ 15N increase from 1.81 ± 0.44‰ to 7.73 ± 1.79‰). The individual N and P concentrations and retention patterns were more species-specific and less responsive to the nutrient limitation gradient. T. orientalis maximised N resorption as N limitation increased (increasing NRE from 50.8 ± 3.3% to 71.7 ± 7.4%; reducing NRP from 0.70 ± 0.12% to 0.36 ± 0.13%) but did not alter PRE or PRP, whereas the S-strategist Schoenus pauciflorus maximised P resorption as P limitation increased (increasing PRE from 48.0 ± 5.6% to 73.5 ± 10.1%; reducing PRP from 0.053 ± 0.008% to 0.015 ± 0.004%) but did not alter NRE or NRP. These results show that the tissue N:P ratio and its associated δ 15N enrichment are highly responsive indicators of the relative availability of N and P at the site and community level. However, they are not indicators of species-specific physiological requirements for N and P, or of likely responses of individual species to N or P enrichment, which are better interpreted from indicators such as RE and RP that describe nutrient retention behaviour.

Variability in amino acid composition of alpine crustacean zooplankton and its relationship with nitrogen-15 fractionation

Amino acids (AAs) are critical biochemical compounds for living organisms. Because of the limited capacity for their de novo synthesis in many animals, the nutritional value of food largely depends on its AA composition relative to the animal's requirements. To improve present knowledge on AA variability in freshwater crustaceans, we studied the inter- and intraspecific variability in three contrasting species from an oligotrophic alpine lake (Daphnia pulicaria, cladocera; Cyclops abyssorum, cyclopoid copepod and Diaptomus cyaneus, calanoid copepod). Inter-species differences were larger than intraspecific variation, confirming a non-strict homeostasis in freshwater crustacean zooplankton. The intraspecific variability differed for each species: in Daphnia, it was mainly related with ontogenetic changes rather than reproduction; in Cyclops, both factors were equally important; and reproduction was the most relevant in Diaptomus. Reproduction changes were associated with serine and phenylalanine in the three species, while the AAs responsible for ontogenetic changes differed in each species. There were no gender differences in AA composition in any of the two copepod species. Free AAs formed a very low percentage of total AA pool (<2.7%). Taking advantage of the fact that Daphnia is the main prey for Cyclops in the lake studied, we further investigated to what extent the AA composition is related with Cyclops-Daphnia nitrogen stable isotope fractionation. Only those AAs that are both essential and are not trans-aminated during protein synthesis had a significant correlation with nitrogen stable isotope fractionation, supporting the hypothesis that an AA imbalance can be responsible for a variable nitrogen stable isotope fractionation.

Effects of nutritional restriction on nitrogen and carbon stable isotopes in growing seabirds

When using stable isotopes as dietary tracers it is essential to consider effects of nutritional state on isotopic fractionation. While starvation is known to induce enrichment of (15)N in body tissues, effects of moderate food restriction on isotope signatures have rarely been tested. We conducted two experiments to investigate effects of a 50-55% reduction in food intake on delta(15)N and delta(13)C values in blood cells and whole blood of tufted puffin chicks, a species that exhibits a variety of adaptive responses to nutritional deficits. We found that blood from puffin chicks fed ad libitum became enriched in (15)N and (13)C compared to food-restricted chicks. Our results show that (15)N enrichment is not always associated with food deprivation and argue effects of growth on diet-tissue fractionation of nitrogen stable isotopes (Delta(15)N) need to be considered in stable isotope studies. The decrease in delta(13)C of whole blood and blood cells in restricted birds is likely due to incorporation of carbon from (13)C-depleted lipids into proteins. Effects of nutritional restriction on delta(15)N and delta(13)C values were relatively small in both experiments (delta(15)N: 0.77 and 0.41 per thousand, delta(13)C: 0.20 and 0.25 per thousand) compared to effects of ecological processes, indicating physiological effects do not preclude the use of carbon and nitrogen stable isotopes in studies of seabird ecology. Nevertheless, our results demonstrate that physiological processes affect nitrogen and carbon stable isotopes in growing birds and we caution isotope ecologists to consider these effects to avoid drawing spurious conclusions.

On the possibility of a kinetic fractionation of nitrogen stable isotopes during natural diamond growth

In a diamond from New South Wales (Australia), cubic and octahedral growth sectors, as identified by cathodoluminescence (CL), show slight differences in N-contents of 29 and 42 ppm respectively but no significant differences in either δ 13C, δ 15N and nitrogen aggregation state with values at +1.96‰, +19.4‰, and 25% Type IaAB aggregation, respectively. Two gem cubes from the Orapa kimberlite (Botswana) were studied by CL revealing a nonfaceted cubic growth. Accordingly, nine other gem cubes were combusted and yielded δ 13C-values from –5.33‰ to –6.63‰, δ 15N from –1.0‰ to –5.5‰, and nitrogen contents from 914 to 1168 ppm, with nitrogen aggregation state being only Type IaA (zero % B). The gem cubes show striking similarities to fibrous/coated diamonds, not only in both δ 13C ranges (less than 3‰ from –5 to –8‰), but also in the high levels of nitrogen (≈ 1000 ppm), suggesting that the two diamond types are related. Additionally, no δ 15N variation was detected between the cube and octahedral growth sectors of the Australian diamond, in the cube sectors of the nine gem cubes from Botswana, nor in fibrous/coated diamonds previously studied. These analyses contrast with an earlier study on a synthetic diamond, which reported a strong kinetic fractionation of N-isotopes of about 40‰ between cube and octahedral growth. The present evidence, therefore, suggests that kinetic fractionation of N-isotopes does not operate during natural diamond formation.

Fractionation of nitrogen stable isotopes by ion exchange chromatography

The ion exchange chromatography displacement technique was used for the enrichment of 15N. The runs were conducted in laboratory and bench scales using two systems of columns filled with Wofatit KPS ion exchange resin (medium porosity type). Ammonia NH4+/NH3 aq. was chosen as the isotopic exchange system. The ammonium bands formed in the columns were eluted by means of sodium hydroxide solution. Hydrodynamic patterns in the column beds was evaluated in terms of dimensionless Reynolds number. The results show that separation process can be performed in the turbulent or laminar flow regime.

Carbon and nitrogen stable isotope fractionation in the sediment of Lake Bled (Slovenia)

Carbon and nitrogen stable isotope fractionation in the sediment of Lake Bled (Slovenia)

Kinetic fractionation of stable nitrogen isotopes during amino acid transamination

This study evaluates a kinetic isotope effect involving 15N, during the transamination reactions catalyzed by glutamic oxalacetic transaminase. During the transfer of amino nitrogen from glutamic acid to oxaloacetate to form aspartic acid, 14NH 2 reacted 1.0083 times faster than 14NH 2. In the reverse reaction transferring NH 2 from aspartic acid to α-ketoglutarate, 14NH 2 was incorporated 1.0017 times faster than 15NH 2. Knowledge of the magnitude and sign of these isotope effects will be useful in the interpretation of the distribution of 15N in biological and geochemical systems.