Two categories of c/c ratios for higher plants

Selected elements and fatty acid composition in human milk as indicators of seafood dietary habits

The maternal diet and living environment can affect levels of chemical elements and fatty acid (FA) composition and their stable isotopes (δ¹³C_FA) in human milk. Information obtained from questionnaires is frequently imprecise, thus limiting proper associations between external and internal exposures as well as health effects. In this study, we focused on seafood as a source of potentially toxic and essential elements and nutritional FAs. Concentrations of selected elements in human milk (As, Cd, Cu, Mn, Pb, Se and Zn) were determined using inductively coupled plasma mass spectrometry (ICP-MS) and Hg using cold vapour atomic-absorption spectrometry (CV-AAS). The identification and quantification of FAs in maternal milk were performed by an in-situ trans-esterification method (FAMEs), and the characterization of FAMEs was performed by gas chromatography with a flame ionisation detector (GC-FID). δ¹³C_FA was determined by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Seventy-four lactating Slovenian women from the coastal area of Koper (KP), with more frequent consumption of seafood, and the inland area of Pomurje (MS), with less frequent seafood consumption, were included in this study. Along with basic statistical analyses, data mining approaches (classification and clustering) were applied to investigate whether FA composition and δ¹³C_FA could improve the information regarding dietary sources of potentially toxic elements. As and Hg levels in milk were found to be statistically higher in populations from KP than in those from MS, and 71% of individual FAs and 30% of individual δ¹³C_FA values in milk differed statistically between the studied areas. In 19 cases, the levels of FAs in milk were higher in KP than in MS; these FAs include C20:5ω3 and C22:6ω3/C24:1ω9, which are typically contained in fish. In 16 cases, the mean percentage of FAs was higher in MS than in KP; these FAs include the PUFAs C18:2ω6, C18:3ω3, and C20:4ω6 which are important for human and infant growth. The difference in δ¹³C levels of C10:0, C12:0, C14:0, C16:1, C16:0, C18:1ω9c, C22:6ω3, and δ¹³C 18:0-16:0 in the study groups was statistically significant. In all seven cases where δ¹³C of FA significantly differed between KP and MS, δ¹³C was higher in KP, indicating a higher proportion of a marine-based diet. The data mining approaches confirmed that the percentage of selected FAs (iC17:0, C4:0, C18:2ω6t, aC17:0, CLA, and C22:4ω6) and δ¹³C_FA of C18:1ω9c in human milk could be used to distinguish between high and low frequency of fresh seafood consumption.

Tracing the geographical origin of rice by stable isotopic analyses combined with chemometrics

Multivariate stable isotope analysis combined with chemometrics was used to investigate and discriminate rice samples from six rice producing provinces in China (Heilongjiang, Jilin, Jiangsu, Zhejiang, Hunan and Guizhou) and four other Asian rice producing countries (Thailand, Malaysia, Philippines, and Pakistan). The stable isotope characteristics were analyzed for rice of different species cultivated with varied farming methods at different altitudes and latitudes/longitudes. The index groups of δ¹³C, δ¹⁵N, δ¹⁸O, ^207/206Pb and ^208/207Pb were screened and established for the selected samples with different geographical features by means of principal component analysis (PCA) and discriminant analysis (DA), which would provide a sound technical solution for rice traceability and serve as a template for further research on the traceability of other agricultural products, especially plant-derived products.

Status, kinship, and place of burial at Early Bronze Age Bab adh-Dhra': A biogeochemical comparison of charnel house human remains

OBJECTIVES

The Early Bronze Age (EBA; ca. 3,600-2000 BCE) of the southern Levant underwent considerable transformation as agro-pastoral communities began to utilize their land more intensively, constructing larger, fortified towns prior to site abandonment at the end of the third millennium. At the site of Bab adh-Dhra' in Jordan, the dead of the Early Bronze (EB) II-III (ca. 3,100-2,500 BCE) period were communally interred within charnel houses, but important disparities between these structures and their contents may be reflective of ownership and use by particular extended kin groups whose activity patterns, subsistence strategies, and even social status may have differed from one another. Subsequently, we hypothesized that differences in mobility and dietary intake may differentiate tomb groups from one another.

MATERIALS AND METHODS

Dental enamel from 31 individuals interred in three different Early Bronze Age charnel houses (A56, A22, A55) at Bab adh-Dhra', Jordan were analyzed for strontium, oxygen, and carbon isotope values.

RESULTS

Strontium isotope ratios (range: 0.70793-0.70842) possessed medians that did not differ statistically from one another, but had ranges that exhibited significant differences in variance. Carbon isotope values ( x ¯ = -13.2 ± 0.5‰, 1σ) were not significantly different.

DISCUSSION

General similarities in human isotopic signatures between EB II-III charnel houses A22 and A55 suggest that their activities were likely similar to one another and agree with findings from excavated domestic spaces with little archaeological evidence for economic, social, or political differentiation. More variable strontium isotope ratios and lower carbon isotope values from A22 could reflect a greater involvement with pastoralist practices or regional trade, including the consumption of more ¹³ C-depleted foods, while those in A55 may have led a more sedentary lifestyle with greater involvement in cultivating orchard crops. All charnel houses contained nonlocal individuals likely originating from other Dead Sea Plain sites with no EB II-III cemeteries of their own, supporting the idea that extended kin groups throughout the region returned to Bab adh-Dhra' to bury their dead.

Carbon and nitrogen isotopic signatures of hair, nail, and breath from tropical African human populations

RATIONALE

Stable isotopic analyses are increasingly used to study the diets of past and present human populations. Yet, the carbon and nitrogen isotopic data of modern human diets collected so far are biased towards Europe and North America. Here, we address this gap by reporting on the dietary isotopic signatures of six tropical African communities: El Molo, Turkana (Kerio), Luhya (Webuye), Luhya (Port Victoria), and Luo (Port Victoria) from Kenya, and Baka from Cameroon; representing four subsistence strategies: fishing, pastoralism, agriculturalism, and hunter-gatherer.

METHODS

We used an elemental analyser coupled in continuous-flow mode to an isotope ratio mass spectrometer to measure the carbon and nitrogen isotopic ratios of hair (n = 134) and nail (n = 80) and the carbon isotopic ratios of breath (n = 184) from these communities, as well as the carbon and nitrogen isotopic ratios of some food samples from the Kenyan communities.

RESULTS

We expand on the known range of δ¹³ C values in human hair through the hunter-gatherer Baka, with a diet based on C₃ plants, and through the agriculturalist Luhya (Webuye), with a diet based on C₄ plants. In addition, we found that the consumption of fish from East African lakes is difficult to detect isotopically due to the combined effects of high nitrogen isotopic ratios of plants and the low nitrogen isotopic ratios of fish. Finally, we found that some of the communities studied are markedly changing their diets through increasing sedentism and urbanisation.

CONCLUSIONS

Our findings contribute substantially to the understanding of the environmental, demographic, and economic dynamics that affect the dietary landscape of different tropical populations of Africa. These results highlight the importance of studying a broader sample of human populations and their diet, with a focus on their precise context - from both isotopic and more general anthropological perspectives.

Caste-specific nutritional differences define carbon and nitrogen fluxes within symbiotic food webs in African termite mounds

Fungus-growing termites of the genus Macrotermes cultivate symbiotic fungi (Termitomyces) in their underground nest chambers to degrade plant matter collected from the environment. Although the general mechanism of food processing is relatively well-known, it has remained unclear whether the termites get their nutrition primarily from the fungal mycelium or from plant tissues partly decomposed by the fungus. To elucidate the flows of carbon and nitrogen in the complicated food-chains within the nests of fungus-growing termites, we determined the stable isotope signatures of different materials sampled from four Macrotermes colonies in southern Kenya. Stable isotopes of carbon revealed that the termite queen and the young larvae are largely sustained by the fungal mycelium. Conversely, all adult workers and soldiers seem to feed predominantly on plant and/or fungus comb material, demonstrating that the fungal symbiont plays a different nutritional role for different termite castes. Nitrogen stable isotopes indicated additional differences between castes and revealed intriguing patterns in colony nitrogen cycling. Nitrogen is effectively recycled within the colonies, but also a presently unspecified nitrogen source, most likely symbiotic nitrogen-fixing bacteria, seems to contribute to nitrogen supply. Our results indicate that the gut microbiota of the termite queen might be largely responsible for the proposed nitrogen fixation.

Axenic growth of the arbuscular mycorrhizal fungus Rhizophagus irregularis and growth stimulation by coculture with plant growth-promoting rhizobacteria

Arbuscular mycorrhizal (AM) fungi are ecologically important for the growth and survival of most vascular plants. These fungi are known as obligate biotrophs that acquire carbon solely from host plants. A ¹³C-labeling experiment revealed the ability of axenically grown Rhizophagus irregularis DAOM 197198 to derive carbon from axenic culture on a relatively novel medium containing two sources of palmitic acid developed by Ishii (designated IH medium). In a separate experiment, this model fungus grew larger mycelia and produced more daughter spores on the IH medium in the presence of two Variovorax paradoxus strains than in axenic culture. In contrast, a strain of Mycobacterium sp. did not influence the growth of the AM fungus. Rhizophagus irregularis produced branched absorbing structures on the IH medium and, in monoxenic culture with V. paradoxus, sometimes formed densely packed hyphal coils. In this study, we report for the first time the formation of coarse terminal pelotons and of terminal and intercalary very fine (≈ 1 μm diameter) hyphal elongations, which could form daughter spores in the presence of V. paradoxus. This study shows the value of IH medium and certain rhizobacteria in the culture of R. irregularis DAOM 197198 in vitro.

Updates to the n-3 polyunsaturated fatty acid biosynthesis pathway: DHA synthesis rates, tetracosahexaenoic acid and (minimal) retroconversion

N-3 polyunsaturated fatty acids (PUFA) and the numerous families of lipid mediators derived from them collectively regulate numerous biological processes. The mechanisms by which n-3 PUFA regulate biological processes begins with an understanding of the n-3 biosynthetic pathway that starts with alpha-linolenic acid (18:3n-3) and is commonly thought to end with the production of docosahexaenoic acid (DHA, 22:6n-3). However, our understanding of this pathway is not as complete as previously believed. In the current review we provide a background of the evidence supporting the pathway as currently understood and provide updates from recent studies challenging three central dogma of n-3 PUFA metabolism. By building on nearly three decades of research primarily in cell culture and oral dosing studies, recent evidence presented focuses on in vivo kinetic modelling and compound-specific isotope abundance studies in rodents and humans that have been instrumental in expanding our knowledge of the pathway. Specifically, we highlight three main updates to the n-3 PUFA biosynthesis pathway: (1) DHA synthesis rates cannot be as low as previously believed, (2) DHA is both a product and a precursor to tetracosahexaenoic acid (24:6n-3) and (3) increases in EPA in response to DHA supplementation are not the result of increased retroconversion.

Compound-specific isotope analysis reveals no retroconversion of DHA to EPA but substantial conversion of EPA to DHA following supplementation: a randomized control trial

BACKGROUND

It has long been believed that DHA supplementation increases plasma EPA via the retroconversion pathway in mammals. However, in rodents this increase in EPA is likely due to a slower metabolism of EPA, but this has never been tested directly in humans.

OBJECTIVE

The aim of this study was to use the natural variations in 13C:12C ratio (carbon-13 isotopic abundance [δ13C]) of n-3 PUFA supplements to assess n-3 PUFA metabolism following DHA or EPA supplementation in humans.

METHODS

Participants (aged 21.6 ± 2.2 y) were randomly assigned into 1 of 3 supplement groups for 12 wk: 1) olive oil control, 2) ∼3 g/d DHA, or 3) ∼3 g/d EPA. Blood was collected before and after the supplementation period, and concentrations and δ13C of plasma n-3 PUFA were determined.

RESULTS

DHA supplementation increased (P < 0.05) plasma EPA concentrations by 130% but did not affect plasma δ13C-EPA (-31.0 ± 0.30 to -30.8 ± 0.19, milliUrey ± SEM, P > 0.05). In addition, EPA supplementation did not change plasma DHA concentrations (P > 0.05) but did increase plasma δ13C-DHA (-27.9 ± 0.2 to -25.6 ± 0.1, P < 0.05) toward δ13C-EPA of the supplement (-23.5 ± 0.22). EPA supplementation increased plasma concentrations of EPA and docosapentaenoic acid (DPAn-3) by 880% and 200%, respectively, and increased plasma δ13C-EPA (-31.5 ± 0.2 to -25.7 ± 0.2) and δ13C-DPAn-3 (-28.9 ± 0.3 to -25.0 ± 0.1) toward δ13C-EPA of the supplement.

CONCLUSIONS

In this study, we show that the increase in plasma EPA following DHA supplementation in humans does not occur via retroconversion, but instead from a slowed metabolism and/or accumulation of plasma EPA. Furthermore, substantial amounts of supplemental EPA can be converted into DHA. δ13C of n-3 PUFA in humans is a powerful and underutilized tool that can track dietary n-3 PUFA and elucidate complex metabolic questions. This trial was registered at clinicaltrials.gov as NCT03378232.

Characterization of coastal wetland soil organic matter: Implications for wetland submergence

High rates of relative sea level rise can cause coastal wetland submergence, jeopardizing the stability of soil organic matter (SOM) sequestered within wetlands. Following submergence, SOM can be lost through mineralization, exported into the coastal ocean, or reburied within adjacent subtidal sediments. By combining measures of soil physicochemical properties, microbial community abundance, organic carbon fractionation, and stable isotope signatures, this study characterized subsurface SOM within a coastal wetland to inform its potential fate under altered environmental conditions. Nine soil cores were collected to a depth of 150 cm from a wetland currently experiencing rapid erosion and submergence within Barataria Bay, LA (USA), and were sectioned into 10 cm intervals. Each soil segment was analyzed to determine total carbon (C), nitrogen (N), phosphorus (P), and stable isotope (δ¹³C and δ¹⁵N) content, as well as extractable ammonium (NH₄⁺), nitrate (NO₃^-), and soluble reactive phosphorus (SRP). Extractable NH₄⁺ and SRP concentrations increased 7× and 11×, respectively, between 0-10 cm and 130-140 cm. Through quantitative PCR, number of gene copies of bacteria and sulfate reduction genes were found to decrease with depth while there was no change in number of gene copies of archaea. This study also demonstrated only small decreases in labile: refractory C ratios with depth; by combining δ¹⁵N data with labile:refractory C ratios and no observed change in C:N ratios with depth, we inferred the presence of minimally processed organic material within deep soils and high nutrient availability, challenging the applicability of the traditional theory of selective preservation and decreased soil quality with depth. As wetland submergence progresses and soils are exposed to oxygenated seawater, this relatively labile SOM and bioavailable N and P stored at depth has the potential for rapid mineralization and/or export into the coastal zone.

Carbon isotope measurements of foods containing sugar: A survey

Over 200 sugars, high sugar content foods, and sugar-free alternative products found in Canadian supermarkets were analyzed for carbon isotope (δ¹³C) values, adding to the record of food items with reported δ¹³C values, which can aid in food authentication and human diet studies. The δ¹³C values of the products were mostly consistent with the photosynthetic pathway of the plant from which the main ingredients were derived. With the exception of those sugars and syrups derived from known C3 sources, all of the sugars and syrups and most of the sugar added to food products were from C4 plants such as sugar cane or corn syrup. Many sweeteners are chemically manufactured, and most reflect an intermediate δ¹³C value. A mixing model estimated the contribution of C3- and C4-based ingredients in foods with high sugar content, which may be used to evaluate the percentage of added sugar from C3- or C4-sources.

From stable isotope ecology to forensic isotope ecology - Isotopes' tales

Stable isotope ecology and forensic isotope ecology are not only linked by name. More often than not, knowledge and insights gained through the former serve as a springboard for application focused work of the latter. This review aims to offer a glimpse into the fascinating world of both though with more emphasis on forensic isotope ecology. To this end a selection of past and recent published work is presented and discussed to highlight both potential and limitations of isotopic analytical approaches to the detection of illegal trade in plants and animals.

Patterns of funerary variability, diet, and developmental stress in a Celtic population from NE Italy (3rd-1st c BC)

Little is known about the types of social organization characterizing the pre-Roman Celtic populations of Italy. Here, we explore the funerary variability characterizing the late Iron Age site of Seminario Vescovile (SV: Verona, Italy, 3rd-1st c. BC), and test its possible correlation to diet and relative exposure to developmental stressors. Patterns on funerary treatment (N = 125), δ13C and δ15N (N = 90), and linear enamel hypoplasia (N = 47) from SV are compared, and their possible association with sex and age-at-death further discussed. Results point to the presence at SV of variable funerary customs while at the same time demonstrating a rather homogenous diet and exposure to developmental stressors: funerary treatment is mainly correlated to age-at-death but do not appear to be associated to either isotopic patterns or hypoplasia frequencies. Accordingly, even if some weak social differentiation may have characterized the individuals buried at SV, this was not reflected in markedly differing living conditions. Our study is the first to attempt an exploration of the links between age, sex, funerary variability, and diet in a pre-Roman Celtic community from Italy. While highlighting the potential of a multifaceted approach in bioarcheology, it also points to a series of analytical and theoretical issues relevant when trying to disentangle the cultural and biological dimensions of social differentiation in the past.

Establishment of a Greek Food Database for Palaeodiet Reconstruction: Case Study of Human and Fauna Remains from Neolithic to Late Bronze Age from Greece

We review the stable isotopic data of recovered Greek bones from the Early Neolithic to the Late Bronze period in order to examine dietary changes over time. As an isotopic baseline we use the published fauna data of the periods. The analysis revealed a diet that included a significant proportion of foods based on C3 plants, and the bulk of the animal protein must have been provided by terrestrial mammals with a small but detectable proportion of marine protein for coastal and island populations. A more significant contribution of marine protein is observed for Bronze Age populations while the enrichment in both C and N isotopes is connected, for some areas, to the introduction of millet during the Bronze Age, and to freshwater consumption. An extensive database of Greek food sources is presented and compared to the fauna from the prehistoric periods (Early Neolithic to Late Bronze Age) of the literature. We propose that this database can be used in palaeodiet reconstruction studies.

Isotope ratio mass spectrometry in antidoping analysis: The use of endogenous reference compounds

RATIONALE

Isotope ratio mass spectrometry (IRMS) is an analytical technique required by the World Antidoping Agency (WADA) before releasing of an adverse finding for the abuse of pseudoendogenous steroids (i.e. testosterone). For every single individual, the delta ¹³ C values (‰) of the selected target compounds (TCs, i.e. testosterone and/or its precursors/metabolites) are compared with those of endogenous reference compounds (ERCs). The aim of this work is to investigate the individual variation in the delta values of four different commonly used ERCs to establish the maximum acceptable variation, in order to detect potential outliers.

METHODS

Routine urine samples collected for antidoping purposes were submitted to IRMS confirmation. After a specific liquid chromatographic purification of the analytes of interest, the final extracts were analyzed by gas chromatography/combustion (GC/C)-IRMS. The selected ERCs monitored were pregnanediol, pregnanetriol, 11-keto-etiocholanolone and 11β-hydroxyandrosterone. The obtained ¹³ C delta values were statistically analyzed to evaluate their inter- and intra-individual distribution.

RESULTS

The delta values of the ERCs studied showed a normal distribution and no major differences among genders were observed. As expected, there are differences depending on the geographical origin of the samples, reflecting different dietary habits and food sources. The intra-individual dispersion, expressed as the standard deviation (SD) of the values of the studied ERCs, did not greatly exceed the instrumental error (0.5‰), demonstrating the good preservation of the delta values along the metabolic pathway.

CONCLUSIONS

For the selected ERCs of non-sporting volunteers and the urinary specimens from more than 1000 sportsmen, we can propose a maximum SD of 0.54‰ and range of 1.2‰ for delta ¹³ C values as acceptance criteria to detect potential outliers. These cases can be caused by the external masking effect of the administration of a substance modifying the delta values or outliers due to unforeseen procedural artifacts.

IRMS as a tool to obtain the carbon turnover (δ13 C) in organs of weaned piglets fed glutamic acid and nucleotides

Early weaning of piglets causes stress characterized by a decrease in feed intake followed by a decline in growth rates; thus, a fast recovery represents an essential step for proper growth of these animals. Considering that IRMS is a potential tool for non-destructive sampling and the fact that it provides time-integrated estimate of assimilated and not just ingested nutrients turned possible its application to evaluate the effects of dietary nucleotides and glutamate on carbon turnover (δ¹³ C) in organs of weanling piglets. At day 0, three piglets were slaughtered (prior to diet switch), the remaining eighty-four piglets weaned at 21-day-old were randomly assigned in a complete block design with a 2 × 2 factorial arrangement of treatments (two Nu levels: 0 and 0.1% and two Glu levels: 0 and 1%), being three piglets per treatment slaughtered on trial days 3, 6, 9, 14, 21, 35 and 49. The samples were analysed by IRMS and adjusted to first-order equation by a non-linear regression analysis using NLIN of SAS, in order to establish exponential graphics. After that, the turnover data were submitted to analysis of variance using GLM of SAS. The turnover value (t_95% ) verified for spleen was faster (p < 0.05) when glutamate was supplemented in diets. For pancreas and liver, the turnover rates were faster (p < 0.05) for the mixture of additives. However, for renal tissue, the turnover rate (t_95% ) was greater (p < 0.05) for the free additive diet. The results obtained suggest that the mixture of additives was more efficient to develop the digestive tract at post-weaning phase, taking into account the functional importance of pancreas and liver for nutrients' digestion and processing.

Carbon input and the structural quality of soil organic matter as a function of agricultural management in a tropical climate region of Brazil

Carbon (C) stabilization and the quality of soil organic matter (SOM) in a tropical climate are key aspects regulating carbon dioxide emissions and maintaining the C cycle. Soil management influences the accumulation of C, regulating the balance between mineralization and/or the humification of SOM. This study aimed to quantify inputs of different chemical forms of C into soil and to evaluate the structural chemical characteristics of humified SOM. Four management systems were established: Forest (F), Pasture (P), Conventional tillage (T), and No-tillage (NT). Total organic carbon (TOC) and nitrogen (TN) by depth, chemical forms of organic matter input, and spectroscopic characterization of SOM in the form of humic acids (HA) were analyzed. The results obtaining by PCA-¹³C NMR show that the forest accumulated a high amount of C on the surface (surpassing 20 Mg ha^-1), favoring the formation of aliphatic HA (C_Alkyl-H,R; C_Alkyl-O,N; C_Alkyl-O). In the NT management that increases biomass in the soil (14 Mg ha^-1), the mineralization process occurred to a greater extent, allowing HA to form with a predominance of aromatic structures (C_Arm-H,R and C_Arm-O,N). The PCA-FTIR analysis showed that the P system contributed to the formation of similar HA to those under F management. The T management system incorporated the least TOC and TN, with different HA types being formed in these soils than what was found in other managements. Thus, minimally managed and more stabilized systems in tropical climates form HA of structural and compositional similarity, regardless of the nature of C (C3 or C4). In contrast, soils subjected to agricultural uses that promote higher or lower C inputs, form HA that are structurally different from P and F. This study demonstrates the need for developing experiments for model building to elucidate the relationships among C input, management type, and the formation of humic substances.

Differentiating pasture honey from eucalyptus honey based on carbon isotopic data in Uruguay

To avoid false declarations of geographic and botanical honey origin, traceability should be based on analytical data, which could then be processed by multivariate statistical methods. Obtaining this data, however, is costly and time consuming. Thus, it would be more convenient to acquire this information from routine trials, for example from the analysis for determination of high fructose corn syrup (HFCS) concentration in honey. The availability of a procedure of this kind in Uruguay would be useful in discriminating between honeys from grasslands to that from eucalyptus, the two main floral sources for commercial production. To this effect, honey samples (47 from pastures and 42 from eucalypts) were analyzed for δ13C in both honey and its protein fraction. We identified a logistic regression model that allowed us to correctly assign 90% of the training samples, using δ13C data of honey, protein fraction, and the isotopic index as variables. This model was then validated, obtaining 100% correct allocation for honeys from pasture and 90% for honeys from eucalyptus. Moreover, we found that this information could also be used to establish adulteration with HFCS based on a local stricter cut-off limit than that of -1.0‰ of the international index.

Three certified sugar reference materials for carbon isotope delta measurements

RATIONALE

For isotope delta analysis, it is preferable to have at least two matrix-matched reference materials whose isotope delta values encompass those of the samples to be analyzed. The National Research Council Canada (NRC) has developed three sugar Certified Reference Materials (CRMs), BEET-1 (beet sugar), GALT-1 (galactose), and FRUT-1 (fructose), to be collectively used for carbon isotope delta measurements in sugars, and other organic materials.

METHODS

All materials were homogenized and packaged in glass ampules. All three sugar materials were analyzed at the NRC using elemental analyzer/isotope ratio mass spectrometry (EA/IRMS). Six additional laboratories also provided EA/IRMS measurements. Data from all laboratories were re-normalized using three international secondary reference materials (IAEA-CH-6, USGS40, and USGS62) included as blind samples in the inter-laboratory comparison, thus providing added quality control and robustness to the study.

RESULTS

Re-normalized carbon isotope delta values from each laboratory were combined using a random laboratory effects statistical model with accounting of the correlations between the laboratory results due to the use of the same reference materials for calibration. The consensus δ(¹³ C) values and combined standard uncertainties which include effects due to characterization, homogeneity, and stability for BEET-1, GALT-1, and FRUT-1 are -26.02(7) ‰, -21.41(6) ‰, and -10.98(5) ‰, respectively, on the VPDB scale.

CONCLUSIONS

Three new δ(¹³ C) sugar CRMs (BEET-1, GALT-1, and FRUT-1) were developed and are available from NRC. These three CRMs can be utilized as a set for daily δ(¹³ C) scale normalization of sugar-based or other organic materials in order to produce reliable δ(¹³ C) measurements.

Do the plant host origins of Helicoverpa (Lepidoptera: Noctuidae) moth populations reflect the agricultural landscapes within which they are caught?

The use of Bt cotton varieties has greatly reduced the amount of conventional insecticides required to control lepidopteran pests, Helicoverpa armigera and Helicoverpa punctigera, in Australia, but the possibility that these moths might become resistant to Bt remains a threat. Consequently, a Resistance Management Plan, which includes the mandatory growing of refuge crops (pigeon pea and non-Bt cotton; both C3 plants), has been established for Bt cotton farmers. However, knowledge of the relative contributions made to overall moth populations from the many host origins (both C3 and C4 plants) available to these insects throughout cotton production regions remains limited, as do the scales of movement and spatial mixing of moths within and between these areas. This study used stable isotope signatures (in particular δ13C) to help identify where moths fed as larvae within separate cotton production regions which differed in their proportions of C3 and C4 host crops (e.g. cotton and sorghum, respectively). C3-derived moths predominated in the early season, but C4-derived moths increased in frequency later. The overall proportion of C4 moths was higher in H. armigera than in H. punctigera. Whilst the relative proportions of C3 and C4 moths differed between regions, no differences in such proportiorns were found at smaller spatial scales, nor were there significant correlations between crop composition and isotope signatures in moths. Overall, these results suggest that C4 host plants are likely to be very important in offsetting the development of Bt resistance in these insects and such influences may operate across multiple regions within a single growing season.

Trace metals, organic carbon and nutrients in the Beidagang Wetland Nature Reserve, northern China

This study aimed to determine sediment contamination in the Beidagang Wetland Nature Reserve to describe atmospheric deposition of trace metals. We analyzed Hg, Cd, Pb, TOC, TN, TP, δ¹³C, and δ¹⁵N, and studied their variations in surface sediments and in the vertical profiles of sediment cores collected from the reserve. Evaluation of environmental trace metal contamination using sediment quality guidelines and geochemical background values indicated that the risk of metal pollution in the reserve sediments was relatively low. Concentrations of Hg, Cd, and Pb in the sediments were much lower than concentrations in sediment samples from Bohai Bay and polluted rivers in Tianjin. Enrichment factors indicate that samples are moderately contaminated with Hg, Cd, and Pb; whereas the geo-accumulation index results classify the sediments as uncontaminated to moderately contaminated with Hg, Cd, and Pb. The distribution patterns of trace metal concentrations in the three core samples were uniform. δ¹³C and δ¹⁵N were used to track the sources of TOC and TN in sediments. Results show that TOC mainly originated from the residue and decaying matter of aquatic plants (e.g., algae, reeds, and Typha), while TN was derived from soil N and elevated atmospheric N deposition. Because domestic and industrial waste is not discharged into the Beidagang Wetland Nature Reserve, trace metals found in sediments mainly originate from atmospheric deposition. The results provide baseline data for analysis of trace metal accumulation in Beijing-Tianjin-Hebei, a region subject to atmospheric deposition in northern China.

Characteristics and compound-specific carbon isotope compositions of sedimentary lipids in high arsenic aquifers in the Hetao basin, Inner Mongolia

Organic matter, as an electron donor, plays a vital role in As mobilization mediated by microorganisms during reductive dissolution of Fe/Mn oxides in shallow aquifers. However, the specific types and sources of organic matter involved in biogeochemical processes accelerating As mobilization are still controversial. Both sediment and groundwater samples were collected at different depths from aquifers of the Hetao Basin, a typical inland basin hosting high As groundwater. Sedimentary lipids and their compound-specific carbon isotope ratios were analyzed to evaluate characteristics and sources of organic matter. Results show that sedimentary As were well correlated with Fe and Mn oxides, suggesting that As exist as Fe/Mn oxide bound forms. Groundwater As far exceeded the drinking water guide value of 10 μg/L. Moreover, As concentrations in shallow groundwater were relatively higher. Lipids in clay were mainly originated from terrestrial higher plants, while that in fine sand samples were derived from terrestrial higher plants, microorganism and petroleum. Shallow fine sand samples were also characterized by evident in-situ biodegradation. Compound-specific carbon isotope compositions of sedimentary lipids showed that short-chain n-alkanes and n-alkanoic acids had more positive δ¹³C values compared to long-chain compounds, especially in shallow fine sand samples. δ¹³C_TOC were also low in shallow fine sand samples. These results jointly indicate that these lipids in shallow fine sand samples acted as carbon source for indigenous microorganism and the short-chain components were particularly more vulnerable to biodegradation, which may contribute to high As concentrations in shallow groundwater. The new findings provide the first evidence that short chain length n-alkyl compounds afforded a source of potential electron donors for microbially mediated As mobilization process in the shallow aquifers.

Jaguar and puma captivity and trade among the Maya: Stable isotope data from Copan, Honduras

From Moctezuma’s zoo to animals kept in captivity at Teotihuacan, there is increasing evidence that Mesoamericans managed wild animals for a myriad of purposes. The present study situates ritualized animal management of highly symbolic fauna in the broader context of Classic Mesoamerica by examining another core site, the Maya center of Copan, Honduras (A.D. 426–822). In this study, we identify two animal populations among the faunal remains from public and private rituals spanning the Copan dynasty. One population, with diets heavily composed of atypically sourced C₄ inputs indicative of artificial feeding, corresponds with the felids interred in Altar Q and Motmot caches. The second population is composed of felids and felid products bearing a predominance of C₃ signatures indicative of a more natural dietary regime. As with Copan deer, species-specific δ¹⁸O variations within these felid populations further substantiates the postulation that an expansive faunal trade network operated throughout the greater Copan Valley and beyond. Animals routed from sites of capture into the mesh of this network would have been processed into pelts, venison and other secondary goods or delivered alive to centers of state power for ritual usage and display. Our data reveal that at Copan, wild animals were routinely brought into intimate contact with human settlements to be managed and physically manipulated in a variety of ways in order to fulfill ritual and symbolic purposes.

Stable carbon and nitrogen isotopic composition of PM10 over Indo-Gangetic Plains (IGP), adjoining regions and Indo-Himalayan Range (IHR) during a winter 2014 campaign

For source identification, a field campaign involving simultaneous sampling of particulate matter (PM₁₀) was conducted at eight sampling sites in the Indian mainland during winter 2014. The sampling sites include Delhi (upper IGP), Lucknow (middle IGP), and Kolkata (lower IGP) in the Indo-Gangetic Plains (IGP); Mohal-Kullu and Darjeeling in the Indo-Himalayan Range (IHR). In addition, Ajmer, located upwind of the IGP in NW-India and Giridih and Bhubaneswar, in the downwind to the IGP has also been chosen. To characterize the sources of the ambient PM₁₀, stable isotope ratios of carbon (δ¹³C_TC) and nitrogen (δ¹⁵N_TN) for the total carbon (TC) and total nitrogen (TN) fractions have been considered. Ancillary chemical parameters, such as organic carbon (OC), elemental carbon (EC), and water-soluble ionic components (WSIC) mass concentrations are also presented in this paper. There was very small variation in the daily average δ¹³C_TC ratios (- 24.8 to - 25.9‰) among the sites. Comparison with end-member stable C isotopic signatures of major typical sources suggests that the PM₁₀ at the sites was mainly from fossil fuel and biofuel and biomass combustion. Daily average δ¹⁵N_TN ratios were not observed to vary much between sites either (8.3 to 11.0‰), and the low δ¹⁵N_TN levels also indicate substantial contributions from biofuel and biomass burning of primarily C3 andC4 plant matter. Graphical abstract Scatter plot of the average (± 1 standard deviation (SD)) δ¹³C_TC (‰) compared to δ¹⁵N_TN (‰) at the sampling sites.

Timing carbon turnover (δ13C) in weaned piglet's brain by IRMS

Isotope-ratio mass spectrometry (IRMS) is a potential tool that provides time-integrated estimate of assimilated and not just ingested nutrients. This feature turned possible its application to evaluate the effects of dietary nucleotides and glutamate on carbon turnover (δ13C) in the brain of weanling piglets. Eighty-seven piglets weaned at 21-day-old were used, being three piglets slaughtered at day-0 (prior to diet-switch) and, the remaining 84 randomly assigned in a complete block design with a 2 x 2 factorial arrangement of treatments (two nucleotide levels: 0% and 0.1% and, two glutamate levels: 0% and 1%). On trial days 3, 6, 9, 14, 21, 35 and 49, three piglets per treatment were also slaughtered. The samples were analyzed by IRMS and adjusted to the first-order equation by a nonlinear regression analysis using NLIN procedure of SAS, in order to obtain the exponential graphics. The carbon turnover (t95%) verified for cerebral tissue was faster (P<0.05) for diet containing glutamate in comparison to other diets, supporting the fact that glutamate contributed to develop the piglets' brain, due to the fastest incorporation of 13C-atoms in this tissue at post-weaning phase, despite the energy deficit experienced by them.

A pilot study on the foraging behaviour of heifers in intensive silvopastoral and monoculture systems in the tropics

Intensive silvopastoral systems (ISS) are a sustainable alternative to monoculture systems (MS). The presence of trees and legumes improves animal welfare due to the increased food quality and quantity and the presence of shade while providing a variety of environmental services. As cattle behaviour is greatly affected by environmental conditions, knowledge on the behavioural trade-offs that cattle make to meet their demands while foraging in different grazing systems is important, as this will help us understand the perceived advantages of ISS. This pilot study assessed the behaviour of heifers in an ISS (n=8 heifers) and MS (n=8 heifers) in the Mexican tropics during the dry and rainy seasons, and its relationship with forage availability, mean travelled distance and the temperature humidity index (THI). In both seasons, daily foraging times were longer in the MS than the ISS (P&lt;0.01). The duration of rumination was higher for ISS (P&lt;0.01) and the duration of lying was higher for the dry season (P&lt;0.05). The decrease in foraging times in relation to THI was significantly higher in the ISS than in the MS (mean slope±SE: ISS=-4.64±0.34; MS=-2.34±0.22; t=-14.20, P&lt;0.001). The results suggest that the forage availability and access to shade in the ISS allow cattle to rest longer and increase rumination, whereas cattle in MS spend more time searching for food and foraging at times of the day were the temperatures were higher as a compensatory strategy, which potentially decreases cattle's welfare and production qualities when compared with the ISS. In conclusion, ISS are likely to generate positive behavioural trade-offs that result in better welfare conditions and higher productive potential.

Of cattle and feasts: Multi-isotope investigation of animal husbandry and communal feasting at Neolithic Makriyalos, northern Greece

The aim of this study is to investigate livestock husbandry and its relationship to the mobilization of domestic animals for slaughter at large communal feasting events, in Late Neolithic Makriyalos, northern Greece. A multi-isotope approach is built that integrates analysis of: δ13C and δ15N values of human and animal bone collagen for understanding long-term dietary behavior,Incremental δ13C and δ18O values of domestic animal tooth enamel carbonate for assessing seasonal patterns in grazing habits and mobility, and87Sr/86Sr ratios of cattle tooth enamel for examining the possibility that some of the animals consumed at the site were born outside the local environment. The findings indicate that cattle had isotopically more variable diets than sheep, which may reflect grazing over a wider catchment area in the local landscape. Cattle products did not make a significant contribution to the long-term dietary protein intake of the humans, which may indicate that they were primarily consumed during episodic feasting events. There is no indication that pasturing of livestock was pre-determined by their eventual context of slaughter (i.e. large-scale feasting vs. more routine consumption events). Two non-local cattle identified among those deposited in a feasting context may have been brought to the site as contributions to these feasts. The evidence presented provides a more detailed insight into local land use and into the role of livestock and feasting in forging social relationships within the regional human population.

Impacts of springtime biomass burning in the northern Southeast Asia on marine organic aerosols over the Gulf of Tonkin, China

Fine particles (PM_2.5) samples, collected at Weizhou Island over the Gulf of Tonkin on a daytime and nighttime basis in the spring of 2015, were analyzed for primary and secondary organic tracers, together with organic carbon (OC), elemental carbon (EC), and stable carbon isotopic composition (δ¹³C) of total carbon (TC). Five organic compound classes, including saccharides, lignin/resin products, fatty acids, biogenic SOA tracers and phthalic acids, were quantified by gas chromatography/mass spectrometry (GC/MS). Levoglucosan was the most abundant organic species, indicating that the sampling site was under strong influence of biomass burning. Based on the tracer-based methods, the biomass-burning-derived fraction was estimated to be the dominant contributor to aerosol OC, accounting for 15.7% ± 11.1% and 22.2% ± 17.4% of OC in daytime and nighttime samples, respectively. In two episodes E1 and E2, organic aerosols characterized by elevated concentrations of levoglucosan as well as its isomers, sugar compounds, lignin products, high molecular weight (HMW) fatty acids and β-caryophyllinic acid, were attributed to the influence of intensive biomass burning in the northern Southeast Asia (SEA). However, the discrepancies in the ratios of levoglucosan to mannosan (L/M) and OC (L/OC) as well as the δ¹³C values suggest the type of biomass burning and the sources of organic aerosols in E1 and E2 were different. Hardwood and/or C₄ plants were the major burning materials in E1, while burning of softwood and/or C₃ plants played important role in E2. Furthermore, more complex sources and enhanced secondary contribution were found to play a part in organic aerosols in E2. This study highlights the significant influence of springtime biomass burning in the northern SEA to the organic molecular compositions of marine aerosols over the Gulf of Tonkin.

Meat provenance: Authentication of geographical origin and dietary background of meat

The authenticity of meat is now an important consideration in the multi-step food chain from production of animals on farm to consumer consumption of the final meat product. A range of techniques, involving analysis of elemental and molecular constituents of meat, fingerprint profiling and multivariate statistical analysis exists and these techniques are evolving in the quest to provide robust methods of establishing the dietary background of animals and the geographical origin of the meat derived from them. The potential application to meat authentication of techniques such as stable isotope ratio analysis applied to different animal tissues, measurement in meat of compounds directly derived from the diet of animals, such as fatty acids and fat soluble vitamins, and spectroscopy is explored. Challenges pertaining to the interpretation of data, as they relate to assignment of dietary background or geographical origin, are discussed.

Impact of industrial phosphate waste discharge on the marine environment in the Gulf of Gabes (Tunisia)

The marine environment in the Gulf of Gabes (southern Tunisia) is severely impacted by phosphate industries. Nowadays, three localities, Sfax, Skhira and Gabes produce phosphoric acid along the coasts of this Gulf and generate a large amount of phosphogypsum as a waste product. The Gabes phosphate industry is the major cause of pollution in the Gulf because most of the waste is directly discharged into the sea without preliminary treatment. This study investigates the marine environment in the proximity of the phosphate industries of Gabes and the coastal marine environment on the eastern coast of Djerba, without phosphate industry. This site can be considered as "pristine" and enables a direct comparison between polluted and “clean” adjacent areas.

Phosphorous, by sequential extractions (SEDEX), Rock-Eval, C, H, N elemental analysis, and stable carbon isotope composition of sedimentary organic matter, X-ray diffraction (qualitative and quantitative analysis) were measured on sediments. Temperature, pH and dissolved oxygen were measured on the water close to the sea floor of each station to estimate environmental conditions. These analyses are coupled with video surveys of the sea floor. This study reveals clear differentiations in pollution and eutrophication in the investigated areas.

Long-term increase in secondary exposure to anticoagulant rodenticides in European polecats Mustela putorius in Great Britain

As a result of legal protection and population recovery, European polecats (Mustela putorius) in Great Britain are expanding into areas associated with greater usage of second-generation anticoagulant rodenticides (SGARs). We analysed polecat livers collected from road casualties from 2013 to 2016 for residues of five SGARs. We related variation in residues to polecat traits and potential exposure pathways, by analysing stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in their whiskers. 54 of 68 (79%) polecats had detectable residues of at least one SGAR. Bromadiolone (71%) was the most frequently detected compound, followed by difenacoum (53%) and brodifacoum (35%). Applying historical limits of detection to allow comparison between these new data and previous assessments, we show that in the 25 years from 1992 to 2016 inclusive, the rate of detection of SGARs in polecats in Britain has increased by a factor of 1.7. The probability of SGAR detection was positively related to increasing values of δ¹⁵N, suggesting that polecats feeding at a higher trophic level were more likely to be exposed. Total concentrations of SGARs in polecats with detectable residues were higher in polecats collected in arable compared to pastoral habitats, and in the west compared to the east of Britain. The number of compounds detected and total concentrations of SGARs increased with polecat age. There was no evidence of regional or seasonal variation in the probability of detecting SGARs, suggesting that the current risk of exposure to SGARs does not vary seasonally and has increased (from that in the 1990s) throughout the polecat's range. We recommend quantification of current practices in rodenticide usage, particularly in the light of recent regulatory changes, to enable assessment and mitigation of the risks of secondary exposure to rodenticides in non-target wildlife.

Historical Tropical Forest Reliance amongst the Wanniyalaeto (Vedda) of Sri Lanka: an Isotopic Perspective

Headland and Bailey (1991) argued in Human Ecology that tropical forests could not support long-term human foraging in the absence of agriculture. Part of their thesis was based on the fact that supposedly isolated 'forest' foragers, such as the Wanniyalaeto (or Vedda) peoples of Sri Lanka, could be demonstrated to be enmeshed within historical trade networks and rely on crops as part of their overall subsistence. Yet, in the same volume and in the years that followed scholars have presented ethnographic and archaeological evidence, including from Sri Lanka, that counter this proposition, demonstrating the occupation and exploitation of tropical rainforest environments back to 38,000 years ago (ka) in this part of the world. However, archaeological and ethnohistorical research has yet to quantify the overall reliance of human foragers on tropical forest resources through time. Here, we report stable carbon and oxygen isotope data from historical Wanniyalaeto individuals from Sri Lanka, in full collaboration with the present-day members of this group, that suggest that while a number of individuals made use of agricultural resources in the recent past, others subsisted primarily on tropical forest resources as late as the 1800s.

Differentiating Organically Farmed Rice from Conventional and Green Rice Harvested from an Experimental Field Trial Using Stable Isotopes and Multi-Element Chemometrics

Chemometric methods using stable isotopes and elemental fingerprinting were used to characterize organically grown rice from green and conventionally grown rice in experimental field trials in China. Carbon, nitrogen, hydrogen, and oxygen stable isotopes as well as 26 other elements were determined. Organic rice was found to be more depleted in ¹³C than green or conventionally grown rice because of the uptake of enriched ¹³C from carbon dioxide and methane respiring bacteria and more enriched in ¹⁵N because of the volatilization of the nitrogen from the urea and ammonium of the animal manures used to manufacture the organic composts. Chemometrics (principal-component analysis and linear-discriminant analysis) were used to separate the three farming methods and provided a promising scientific tool to authenticate the farming methods of different rice cultivars fertilized with animal manures, green composts, and synthetic fertilizers in China or elsewhere.

Origin of Xylitol in Chewing Gum: A Compound-Specific Isotope Technique for the Differentiation of Corn- and Wood-Based Xylitol by LC-IRMS

The sugar replacement compound xylitol has gained increasing attention because of its use in many commercial food products, dental-hygiene articles, and pharmaceuticals. It can be classified by the origin of the raw material used for its production. The traditional "birch xylitol" is considered a premium product, in contrast to xylitol produced from agriculture byproducts such as corn husks or sugar-cane straw. Bulk stable-isotope analysis (BSIA) and compound-specific stable-isotope analysis (CSIA) by liquid-chromatography isotope-ratio mass spectrometry (LC-IRMS) of chewing-gum extracts were used to determine the δ¹³C isotope signatures for xylitol. These were applied to elucidate the original plant type the xylitol was produced from on the basis of differences in isotope-fractionation processes of photosynthetic CO₂ fixation. For the LC-IRMS analysis, an organic-solvent-free extraction protocol and HPLC method for the separation of xylitol from different artificial sweeteners and sugar-replacement compounds was successfully developed and applied to the analysis of 21 samples of chewing gum, from which 18 could be clearly related to the raw-material plant class.

Characterizing isotopic compositions of TC-C, NO3--N, and NH4+-N in PM2.5 in South Korea: Impact of China's winter heating

The origin of PM_2.5 has long been the subject of debate and stable isotopic tools have been applied to decipher. In this study, weekly PM_2.5 samples were simultaneously collected at an urban (Seoul) and rural (Baengnyeong Island) site in Korea from January 2014 through February 2016. The seasonal variation of isotopic species showed significant seasonal differences with sinusoidal variation. The isotopic results implied that isotope species from Baengnyeong were mostly originated from coal combustion during China's winter heating seasons, whereas in summer, the isotopic patterns observed that were more likely to be from marine. In Seoul, coal combustion related isotopic patterns increased during China's winter heating period while vehicle related isotopic patterns were dominated whole seasons by default. Therefore, aerosol formation was originated from long-range transported coal combustion-related NO_x by vehicle-related NH₃ in Seoul. δN-NH₄⁺ in Seoul showed highly enriched ¹⁵N compositions in all seasons, indicating that NH₃ from vehicle emission is the important source of NH₄⁺ in PM_2.5 in Seoul. In addition, Baengnyeong should be consistently considered as a key region for observing the changes of isotopic features depend on the contribution of individual emissions to the atmospheric as a result of the reduction of coal consumption in China.

Atmospheric CO2 effect on stable carbon isotope composition of terrestrial fossil archives

The 13C/12C ratio of C3 plant matter is thought to be controlled by the isotopic composition of atmospheric CO2 and stomatal response to environmental conditions, particularly mean annual precipitation (MAP). The effect of CO2 concentration on 13C/12C ratios is currently debated, yet crucial to reconstructing ancient environments and quantifying the carbon cycle. Here we compare high-resolution ice core measurements of atmospheric CO2 with fossil plant and faunal isotope records. We show the effect of pCO2 during the last deglaciation is stronger for gymnosperms (-1.4 ± 1.2‰) than angiosperms/fauna (-0.5 ± 1.5‰), while the contributions from changing MAP are -0.3 ± 0.6‰ and -0.4 ± 0.4‰, respectively. Previous studies have assumed that plant 13C/12C ratios are mostly determined by MAP, an assumption which is sometimes incorrect in geological time. Atmospheric effects must be taken into account when interpreting terrestrial stable carbon isotopes, with important implications for past environments and climates, and understanding plant responses to climate change.

Drought Sensitivity of the Carbon Isotope Composition of Leaf Dark-Respired CO2 in C3 (Leymus chinensis) and C4 (Chloris virgata and Hemarthria altissima) Grasses in Northeast China

Whether photosynthetic pathway differences exist in the amplitude of nighttime variations in the carbon isotope composition of leaf dark-respired CO2 (δ13Cl) and respiratory apparent isotope fractionation relative to biomass (ΔR,biomass) in response to drought stress is unclear. These differences, if present, would be important for the partitioning of C3-C4 mixed ecosystem C fluxes. We measured δ13Cl, the δ13C of biomass and of potential respiratory substrates and leaf gas exchange in one C3 (Leymus chinensis) and two C4 (Chloris virgata and Hemarthria altissima) grasses during a manipulated drought period. For all studied grasses, δ13Cl decreased from 21:00 to 03:00 h. The magnitude of the nighttime shift in δ13Cl decreased with increasing drought stress. The δ13Cl values were correlated with the δ13C of respiratory substrates, whereas the magnitude of the nighttime shift in δ13Cl strongly depended on the daytime carbon assimilation rate and the range of nighttime variations in the respiratory substrate content. The ΔR,biomass in the C3 and C4 grasses varied in opposite directions with the intensification of the drought stress. The contribution of C4 plant-associated carbon flux is likely to be overestimated if carbon isotope signatures are used for the partitioning of ecosystem carbon exchange and the δ13C of biomass is used as a substitute for leaf dark-respired CO2. The detected drought sensitivities in δ13Cl and differences in respiratory apparent isotope fractionation between C3 and C4 grasses have marked implications for isotope partitioning studies at the ecosystem level.

Characteristics of soil C:N ratio and δ13C in wheat-maize cropping system of the North China Plain and influences of the Yellow River

To better understand the characteristics of soil organic matter (SOM) in the North China Plain, we evaluate the large scale variations of soil organic carbon (SOC), total nitrogen (TN), carbon to nitrogen (C:N) ratio and stable carbon isotopic compositions (δ¹³C) in SOC over 0-100 cm. To assess the influence of the Yellow River, 31 sites are selected from the wheat-maize double cropping system, and grouped into two: 10 sites near and 21 sites far from the river. Our data show that mean soil C:N ratio is low (7.6-9.9) across the region, and not affected by the Yellow River. However, SOC and TN are significantly (P < 0.05) lower in subsoil near the Yellow River (2.0 and 0.2-0.3 g kg^-1 for SOC and TN) than far away (3.1 and 0.4 g kg^-1); δ¹³C is significantly more negative below 60 cm near the river (-23.3 to -22.6‰) than far away (-21.8 to -21.4‰). We estimate that the contributions of wheat and maize to SOC are 61.3-68.1% and 31.9-38.8%, respectively. Our analyses indicate that the overall low levels of SOC in the North China Plain may be associated with the low soil C:N ratio and less clay content. The hydrological processes may also partly be responsible, particularly for those near the Yellow River.

Altered humin compositions under organic and inorganic fertilization on an intensively cultivated sandy loam soil

Humin is the most recalcitrant fraction of soil organic matter (SOM). However, little is known about quantitative structural information on humin and the roles of soil mircoorganisms involved in the humin formation. We applied advanced solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy to provide deep insights into humin structural changes in response to long-term balanced fertilization on a Calcaric Fluvisol in the North China plain. The relationships between humin structure and microbiological properties such as microbial biomass, microbial quotient (q_mic) and metabolic quotient (qCO₂) were also studied. The humins had a considerable (35-44%) proportion of aromatic C being nonprotonated and the vast majority of O-alkyl and anomeric C being protonated. Alkyl (24-27% of all C), aromatic C (17-28%) and O-alkyl (13-20%) predominated in humins. Long-term fertilization promoted the aliphatic nature of humins, causing increases in O-alkyl, anomeric and NCH functional groups and decreases in aromatic C and aromatic CO groups. All these changes were more prominent for treatments of organic fertilizer (OF) and combined mineral NPK fertilizer with OF (NPKOF) relative to the Control and NPK treatments. Fertilization also decreased the alkyl/O-alkyl ratio, aromaticity and hydrophobic characteristics of humins, suggesting a more decomposed and humified state of humin in the Control soil. Moreover, the soil microbiological properties had strong correlations with functional groups of humins. Particularly, microbial biomass C was a relatively sensitive indicator, having positive correlations with oxygen-containing functional groups, i.e., COO/NCO and protonated O-alkyl C, and negative correlations with nonprotonated aromatic C. The q_mic and qCO₂ were also significantly positively correlated with NCH and aromatic CO, respectively. Our results deepen our understanding of how long-term fertilization impacts the structure of humin, and highlight a linkage between microbiological properties and recalcitrant fraction of SOM besides labile fraction.

Using 13C in cattle hair to trace back the maize level in the feeding regime-A field test

Sections from cattle hair serve as an isotopic archive-they contain information on the cattle diet from different time periods. We tested the reliability of 13C signatures (δ13C) in cattle tail switch hair to retrospectively trace back the annual dietary proportion of maize of different production systems without having to sample and analyze the feed. Furthermore, we investigated if differences in dietary proportion of maize during summer and winter feeding can be detected in a single tail switch hair by sampling hair only once a year. We sampled hair and obtained information on management and annual composition of diets on 23 cattle farms in northern Germany. Farms differed in dietary proportions of maize, grass and concentrates as well as in grazing regime (year-round grazing, summer grazing, no grazing). We found that the annual mean δ13C values (δ13CY) of two hair sections that contain the isotopic information of summer and winter feeding is a robust indicator for the annual proportion of maize in cattle diet on a farm. The grazing regimes could clearly be distinguished by analyzing seasonal mean δ13C values (δ13CS). We could also demonstrate short term changes in the diet changes by means of δ13CS. We conclude that the method can be used in different cattle production systems to check on dietary proportions of maize for a period of one year before sampling of hair.

Retroconversion is a minor contributor to increases in eicosapentaenoic acid following docosahexaenoic acid feeding as determined by compound specific isotope analysis in rat liver

Dietary docosahexaenoic acid (DHA, 22:6n-3) not only increases blood and tissue levels of DHA, but also eicosapentaenoic acid (EPA, 20:5n-3). It is generally believed that this increase is due to DHA retroconversion to EPA, however, a slower conversion of α-linolenic acid (ALA, 18:3n-3) derived EPA to downstream metabolic products (i.e. slower turnover of EPA) is equally plausible. In this study, 21-day old Long Evans rats were weaned onto an ALA only or DHA + ALA diet for 12 weeks. Afterwards, livers were collected and the natural abundance ¹³C-enrichment was determined by compound specific isotope analysis (CSIA) of liver EPA by isotope ratio mass-spectrometry and compared to dietary ALA and DHA ¹³C-enrichment. Isotopic signatures (per mil, ‰) for liver EPA were not different (p > 0.05) between the ALA only diet (−25.89 ± 0.39 ‰, mean ± SEM) and the DHA + ALA diet (−26.26 ± 0.40 ‰), suggesting the relative contribution from dietary ALA and DHA to liver EPA did not change. However, with DHA feeding estimates of absolute EPA contribution from ALA increased 4.4-fold (147 ± 22 to 788 ± 153 nmol/g) compared to 3.2-fold from DHA (91 ± 14 to 382 ± 13 nmol/g), respectively. In conclusion, CSIA of liver EPA in rats following 12-weeks of dietary DHA suggests that retroconversion of DHA to EPA is a relatively small contributor to increases in EPA, and that this increase in EPA is largely coming from elongation/desaturation of ALA.

Speciation and Sources of Brown Carbon in Precipitation at Seoul, Korea: Insights from Excitation-Emission Matrix Spectroscopy and Carbon Isotopic Analysis

Brown carbon (BrC) plays a significant role in the Earth's radiative balance, yet its sources and chemical composition remain poorly understood. In this work, we investigated BrC in the atmospheric environment of Seoul by characterizing dissolved organic matter in precipitation using excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC). The two independent fluorescent components identified by PARAFAC were attributed to humic-like substance (HULIS) and biologically derived material based on their significant correlations with measured HULIS isolated using solid-phase extraction and total hydrolyzable tyrosine. The year-long observation shows that HULIS contributes to 66 ± 13% of total fluorescence intensity of our samples on average. By using dual carbon (¹³C and ¹⁴C) isotopic analysis conducted on isolated HULIS, the HULIS fraction of BrC was found to be primarily derived from biomass burning and emission of terrestrial biogenic gases and particles (>70%), with minor contributions from fossil-fuel combustion. The knowledge derived from this study could contribute to the establishment of a characterizing system of BrC components identified by EEM spectroscopy. Our work demonstrates that, EEM fluorescence spectroscopy is a powerful tool in BrC study, on the basis of its chromophore resolving power, allowing investigation into individual components of BrC by other organic matter characterization techniques.

Kinetic and equilibrium based fractionation study of Pb in continental shelf sediment of India

Two independent analytical methods (kinetic and sequential extraction protocols) were used to understand the distribution, stability, and lability of Pb-sediment complexes in Indian continental shelf. The concentrations of sedimentary Pb varied from 12.0±0.6 to 30.4±0.1mg·kg^-1 and 15.9±0.3 to 36.7±0.4mg·kg^-1 in the western and eastern shelf of India respectively. The kinetic extraction study showed that higher proportion of labile Pb-complexes were present in the eastern shelf sediments (~24% of total Pb) than the western shelf sediments (~14% of total Pb). The sedimentary organic matter was found to regulate lability of sedimentary Pb complexes. The sequential extraction study suggested that Fe/Mn oxyhydroxide were the primary hosting phase for labile Pb complexes. This study showed that water soluble, exchangeable, carbonate/bicarbonate-Pb complexes in the sediments was labile. This study provides a better physicochemical description of stability or lability of Pb complexes in the coastal sediment of India.