Nitrogen Isotope Research Articles

Leaf-level physiological strategies related to productivity and plasticity of Populus in the Southeastern United States

IntroductionPopulus and its hybrids are attractive bioenergy crops and the southeastern United States has broad ability to supply bioenergy markets with woody biomass. Breeding and hybridization have led to superior eastern cottonwood (Populus deltoides W. Bartram ex Marshall) and hybrid poplars adapted to a wide variety of site types not suited for agricultural production. In order to maximize productivity and minimize inputs, genotypes need to efficiently use available site resources and tolerate environmental stresses. In addition, we need to determine plasticity of traits and their coordination across sites to select traits that will broadly characterize genotypes. Therefore, our study objectives were to determine (1) which leaf traits were correlated with growth, (2) if traits and genotypes exhibited significant plasticity across sites, and (3) how traits were coordinated within and across sites and Populus taxa.MethodsWe measured trees at two sites in northeastern Mississippi, United States: one upland and one alluvial terrace site. Genotypes included eastern cottonwoods as well as F1 crosses of eastern cottonwood and P. maximowiczii (Henry), P. nigra (L.) and P. trichocarpa (Torr. & Gray).ResultsWe found that sites differed in which leaf traits were correlated with productivity; with water use efficiency specifically being positively correlated with growth at an alluvial terrace site, but negatively correlated with growth at an upland site. Tree height growth, leaf isotope composition (δ13C and δ15N), as well as leaf mass per area (LMA) exhibited the least plasticity across sites, while physiological gas exchange parameters and leaf nitrogen concentration exhibited the highest plasticity. Broadly across taxa, leaf carbon isotope ratios were correlated with intrinsic water use efficiency, and stomatal conductance was positively correlated with photosynthetic nitrogen use efficiency across sites, while leaf nitrogen isotope ratios exhibited contrasting relationships with leaf nitrogen concentration.DiscussionOverall, these results allow us to refine selections of productive genotypes based on site conditions and site-specific relationships with physiological parameters to better match Populus taxa with sites and landowner objectives.

Composition and Content of Fatty Acids in Muscle Tissue of the Potanin Altai Osman <i>Oreoleuciscus potanini</i> (Cypriniformes, Actinopterigii) from Mongolian Reservoirs

The composition of fatty acids in the muscle tissue of the unique Central Asian carp-like fish of the Potanin Altai osman Oreoleuciscus potanini was studied for the first time. The populations of these fish in the reservoirs of the semi-desert zone (Durgun and Taishir) during the period of their formation are considered. It was shown that the content of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in O. potanini corresponds to the median value of this value in the order Cypriniformes. It has been established that the basis of the food web of the herbivorous form of this species consists of microalgae: diatoms, euglens and, possibly, chrysophytes, as well as bacteria. At the same time, the levels of bacterial biomarkers, 15–17BFA and 17:0 were significantly higher in fish in the Durgun reservoir, and the level of EPA (diatom biomarker) in O. potanini in the Taishir reservoir. The established higher values of the heavy nitrogen isotope content in the muscles of O. potanini from the Taishir reservoir are most likely associated with not yet formed benthic communities and with the incomplete diversification of the river form of the Potanin Altai Osman into lacustrine forms.

Insights from stable isotope and fatty acid analyses on the diet of an Antarctic nudibranch

Reconstructing predator-prey interactions in a biological community provides a better understanding of species’ ecological roles and helps predict how changes in one component will affect the others. Doris kerguelenensis is an Antarctic heterobranch mollusc that feeds on sponges, according to previous gut content analyses. Here, stable isotopes of carbon and nitrogen (δ 13C and δ15N) and fatty acids (FAs) were used to assess the relative contribution of several species of demosponges (Axinella crinita, Dendrilla antarctica, Hemigellius pilosus, Kirkpatrickia variolosa, Mycale acerata, Sphaerotylus antarcticus, and Haliclona sp.) to D. kerguelenensis diet. Particulate organic matter and 2 macroalgae species were also analyzed to better characterize the diversity of sources fueling the food web. The δ15N values of the sponges suggest a trophic position of 2-3 for A. crinita, D. antarctica, M. acerata, and Haliclona sp. and of 3-4 for H. pilosus and S. antarcticus. Mixing models failed to resolve the nudibranch diet, either because the sponges were too enriched in 13C or because the diet-to-tissue discrimination factor values available in the literature for gastropods are unsuitable for this nudibranch species. The high abundance of bacterial FA markers in H. pilosus, S. antarcticus, and K. variolosa, and their high δ15N values, rule them out as major prey for D. kerguelenensis. The overall evidence suggests that A. crinita, D. antarctica, M. acerata, and Haliclona sp. are consumed regularly by D. kerguelenensis but do not represent its only dietary sources. Hence, the analysis of biomarkers refutes the previously established role of D. kerguelenensis as a specialized spongivore.

Pollution affects even oceanic marine protected areas in Southwestern Atlantic.

Reefs are facing a global decline with sewage pollution emerging as a significant and poorly understood threat. Inadequate wastewater management and disorderly urbanization contributes to water pollution globally. Tropical Southwestern Atlantic comprises a set of oceanic Marine Protected Areas (MPAs) including the Fernando de Noronha Archipelago in Brazil, which has experienced significant population growth without expanding the sewage infrastructure. We mapped and quantified marine pollution in these MPAs, characterizing pollution sources and evaluating their effects on benthic and fish communities in 13 reef sites. We quantified nutrients, metals and metalloid, microplastics, fecal sterols, and Polycyclic Aromatic Hydrocarbons (PAHs) in both water and sediment samples. We also used isotopic tracing on macroalgae to identify the origin of organic matter and characterized benthic and fish communities, and algae biomass at each site. Pollution was more pronounced in the multiple-use area but also affected no-take areas. Effluents from wastewater treatment plants did not meet legislative standards, and reefs in the multiple-use area were enriched in orthophosphate and ammonia compared to those in the no-take area. Nitrogen isotopes in macroalgae revealed sewage-derived nitrogen throughout the multiple-use area. Nutrient enriched sites exhibited higher abundances of fast-growing and opportunistic green macroalgae, and higher biomass of brown macroalgae. The port area, within the multiple-use area, showed high PAHs, coprostanol and metal(loid) concentrations, suggesting untreated sewage and nautical chemical pollution. Microplastics were widespread in sediment and water samples. We documented the pervasive impacts of marine pollution on reef habitats even within marine protected areas in oceanic regions, demonstrating that local pollution control, sewage management and regulating procedures in port areas are critical to protect marine ecosystems. Comparisons with previous studies suggest marine pollution has substantially increased in the Archipelago in the last ten years. This is the first comprehensive assessment of marine pollution in an oceanic environment in Southwestern Atlantic, showing these isolated environments are not immune to pollution impacts.

Seasonal variations and hydrological management regulate nutrient transport in cascade damming: Insights from carbon and nitrogen isotopes

Reservoirs around the world have significantly altered the natural transport of nutrients in rivers. However, the specific effects of the cascade damming on the migration, transformation, and environmental consequences of these nutrients remain unclear. To address this knowledge gap, we analyzed spatiotemporal variations in water chemistry, nutrient concentrations, stable isotope of dissolved inorganic carbon (δ13CDIC) and nitrate isotope (δ15N-NO3-) in seven cascade reservoirs along the Wujiang River, each characterized by different regulatory regimes. Our findings reveal that the average absolute changes in concentrations of total nitrogen (TN), total phosphorus (TP), and silicon dioxide (SiO2) during the wet season (WS, spring and summer) were 2.4, 1.4, and 1.1 times higher than those observed in the dry season (DS, autumn and winter). During the WS, the average apparent retention efficiency (*RETf) values in the Hongjiadu reservoir were 97 % for TN, 98 % for TP, and 95 % for SiO2, indicating substantial nutrient consumption in the cascading reservoirs. Conversely, during the DS, the *RETf values for TN, TP, and SiO2 were negative, suggesting notable nutrient accumulation within the reservoirs. The nutrient fluxes released downstream from the cascade reservoirs in the Wujiang River were significantly greater than the upstream inflow fluxes. These findings help demonstrate how downstream discharge across cascade reservoirs amplifies nutrient flux disparities due to dam construction. Our study enhances the understanding of how cascade dam construction impacts nutrient dynamics, supporting the optimization of reservoir operation models and advancing scientific water resource management and conservation efforts.

Decadal oscillations in the ocean's largest oxygen-deficient zone.

The impact of global warming on the ocean's oxygen-deficient zones (ODZs) is uncertain, partly because of a lack of data on past changes. We report monthly resolved records of coral skeleton-bound nitrogen isotopes (CS-δ15N) to reconstruct denitrification in the Eastern Tropical North Pacific (ETNP) ODZ over the last 80 years. The data indicate strong decadal variation in ETNP denitrification, with maxima during the cool North Pacific phase of Pacific Decadal Variability. The maxima in denitrification (and thus oxygen deficiency) were likely due to stronger upwelling that enhanced productivity leading to greater oxygen demand in the thermocline. Prior findings of multidecadal-to-centennial ODZ trends were likely biased by this variability. ODZ evolution over the next century will depend on how global warming interacts with the decadal oscillations.

A Strong Link Between Oceanographic Conditions and Zooplankton δ13C and δ15N Values in the San Jorge Gulf, Argentina

Maps of (baseline) δ13C and δ15N values of primary producers or consumers near the base of food webs provide crucial information for interpreting patterns in the isotopic composition of consumers that occupy higher trophic levels. In marine systems, understanding how oceanographic variables influence these values enables the creation of dynamic isoscapes across time and space, providing insights into how ecosystems function. The San Jorge Gulf (SJG) in the southwest Atlantic Ocean (45° S–47° S) is an area of particular importance, as it is located on one of the most productive continental shelves in the world, supporting large fisheries and marine mammal and seabird populations. We reconstructed spatial variation in zooplankton δ13C and δ15N values across SJG and investigated their relationship with physical and chemical oceanographic conditions. During cruises in the austral spring of 2016 and 2017, we collected medium-sized copepods whose isotopic composition integrate short-term (days to weeks) variation in oceanographic conditions recorded by phytoplankton at the base of the food web. We also collected data on water column depth, surface and bottom temperatures, water column stability, and macronutrient (nitrate, phosphate, and silicic acid) concentrations. The results revealed significant variation in both δ13C and δ15N values of up to 7-8‰ over a relatively small spatial scale (200–300 km). Copepod δ13C values were lower at the center of the SJG, showing an inverse correlation with water column stability, surface nitrate concentration, and water column depth. δ15N values showed a strong and negative relationship with surface nitrate concentration and water column stability, increasing from south to north in the SJG. δ15N values also showed a positive relationship with surface silicic acid concentration. These spatial patterns in nutrient dynamics and copepod carbon and nitrogen isotope values are interpreted in the context of the dominant northward current and temporal development of the frontal systems in the SJG.

The dynamics of Bovini exploitation strategies on the Central Plains of China from the Middle Neolithic to the Bronze Age

Bos and Bubalus are important Bovini resources worldwide and were widely exploited on the Central Plains of China during the Neolithic and Bronze Ages. However, distinguishing between Bos and Bubalus remains were challenging due to their similar morphological traits, which leaves the interaction between them poorly understood. This study is the first to combine Zooarchaeology by Mass Spectrometry (ZooMS) with zooarchaeological methods to identify Bos and Bubalus in China at the Tuchengwang (5600–4300 cal. BP), and Pingliangtai (4200–3900 cal. BP) sites. This was accompanied by carbon and nitrogen isotope analyses of bone collagen to discuss their diets on the Central Plains. Our findings indicate that these exploitation strategies are dynamic. Aurochs (Bos primigenius) and water buffaloes (Bubalus mepistopheles) were exploited before the introduction of cattle (Bos taurus), and this exploitation continued into the Bronze Age. The exploitation of local wild Bovini resources may have influenced the adoption of cattle during the End Neolithic. By this time, cattle predominated in Bovini remains at most sites, but the adoption of cattle was not a phenomenon of unison, and their exploitation strategies became more diverse, especially in ritual practices. Wild water buffaloes had evolved into privilege goods by the Bronze Age, especially during the late Shang. This study contributes to a deeper understanding of human-animal-environment relationships between Bovini and ancient people.

Characteristics of Stable Carbon and Nitrogen Isotopes in Different Ecological Plant Groups and Sediments Collected from 14 Softwater Lakes in Poland

Softwater lakes with specific, rare, and protected aquatic plant vegetation are very sensitive to increased trophic and water chemical changes, especially alkalization. These changes might be reflected in the stable carbon and nitrogen isotopes of the organic matter (OM) of those plants (δ13CORG and δ15NORG) and sediments (δ13CORG and δ15NTN) which they cocreated. To recognize the relationship between OM in the aquatic plants of softwater lakes and the cocreated sediments, we analyzed the plants δ13CORG and δ15NORG in light of four ecological groups (as well as the sediments δ13CORG and δ15NTN in which these plants thrived). Studies were performed in July 2020 on 14 softwater lakes in northern Poland with varying pH gradients from 4.86 to 9.20. For each lake, a single stand was examined for each species detected. The goal was to investigate each species at 10 sites, but this target was not reached for several species. Among the investigated ecological groups, isoetids and mosses showed the least variation in obtained values. In contrast, elodeids exhibited the highest variation in δ13C results due to their diverse carbon uptake strategies, involving both CO2 and HCO3− forms. Moreover, the δ13C values of charophytes and elodeids were highly related to the increasing pH of water. The slight differences between the δ13C results of plants and sediments in isoetid stands further support this finding. Furthermore, we noticed an increase in sediment δ13CORG values along the alkalization gradient, suggesting that macrophytes were the primary source of OM for the sediments. The positive correlation between the δ13C values of plants and sediments (r = 0.69, p < 0.05) might also confirm that the macrophytes were a significant source of OM in sediments. Regarding δ15N values, we did not find significant differentiation between plants and sediments across ecological groups. However, sediment consistently exhibited 15N-enrichment compared to plant material. This enrichment is likely attributed to the accumulation of 15N during the decomposition of the deposited material. This study confirms the possibility of tracking changes in the aquatic vegetation of softwater lakes based primarily on the sediment δ13CORG values along the alkalization gradient.

A Proof-of-Principle Study for δ15N Measurements of Aqueous Dissolved Nitrate With a Modified LC-IRMS Interface.

The analysis of nitrogen isotopes in aqueous dissolved nitrate is an effective method for identifying pollution sources and offers the potential to study the nitrogen cycle. However, the measurement of nitrogen isotope ratios of nitrate still requires extensive sample preparation or derivatization. In this study, a modified commercially available liquid chromatography-isotope ratio mass spectrometer (LC-IRMS) interface is presented that enables automated measurement of δ15N signatures from nitrate by online reduction of nitrate in two consecutive steps. First, vanadium(III) chloride is used as a reducing agent to convert NO3 - to NxOy under acidic conditions. The mix of nitrogen oxides is then transferred into a stream of helium and reduced to nitrogen (N2) analysis gas via a hot copper reactor. Prior to the online conversion of aqueous nitrate into elemental nitrogen, the sample was chromatographically separated from potential matrix effects on a PGC column. Precision was achieved at a level below 1.4‰ by injecting 10 μL of 50 mg L-1 N, using five different nitrate standards and reference materials. These materials spanned a range of more than 180‰ in δ15N. To demonstrate the applicability of the method, we measured water samples from an enrichment experiment, where isotopically enriched ammonium chloride was administered into a small river over the course of 2 weeks. In contrary to our expectation, the δ15N values of river nitrate showed values between +0.4 ± 0.4‰ and +4.1 ± 0.3‰, varying over a small range of 3.7‰. Our study showed that the measurement of nitrate nitrogen isotope ratios with a modified LC-IRMS system is possible but that further modifications and improvements would be necessary for a robust and user-friendly instrument.

DFT-SCRF Calculations of Nitrogen Isotopic Reduced Partition Function Ratios for Amino Acids in Aqueous Solution at pH 7.4.

Using the self-consistent reaction field (SCRF) method, the nitrogen isotopic reduction partition function ratio (RPFR), a fundamental physical quantity for theoretical consideration of equilibrium isotope effects, was evaluated by density functional theory (DFT) for 20 proteinogenic and two related amino acids under physiological conditions at pH 7.4. At this pH value, all amino acids were of the zwitterion-type form with α-NH3+ and α-COO- groups, regardless of the net charge of -1 (monoanion), 0 (zwitterion), or +1 (monocation). The largest RPFR value by far was for proline (Pro). This is due to the fact that the nitrogen atom of Pro has two C-N bonds and two N-H bonds, whereas the α-nitrogen atoms of other amino acids form one C-N bond and three N-H bonds. There was a clear correlation between the RPFR value of α-nitrogen and the distance of the N-H covalent bond of the hydrogen atom involved in the formation of the intramolecular hydrogen bond (HB); the stronger the intramolecular HB, the lower the RPFR value of α-nitrogen. It was suggested that equilibrium isotope effects were partially responsible for the nitrogen isotope fractionation in the enzymatic glutamic acid/aspartic acid transamination and in ammonia assimilation during the formation of glutamine from glutamic acid.

The molybdenum cycle in the oxygenated Neoproterozoic ocean was coupled to manganese carbonate mineralization

The Neoproterozoic oxygenation event is a milestone in Earth’s history, yet the redox structure and elemental cycling of the Neoproterozoic ocean remain debated. Here, we investigated iron speciation, molybdenum, and nitrogen isotopes in black shales and manganese carbonates from the upper Ediacaran Doushantuo Formation, South China, to examine the links between redox state, manganese mineralization, and molybdenum cycling. In both lithologies, high pyritic iron ratios (> 0.8) indicate a localized euxinic zone, while estimated seawater molybdenum (1.9‰) and sediment nitrogen isotopic compositions (4.19 ± 1.96‰) resemble modern values, suggesting oxygenated surface waters over euxinic depths. Negative molybdenum isotope in manganese(II) carbonates points to manganese(IV) oxide reduction, acting as a molybdenum shuttle from oxygenated surface to euxinic deep waters. Periodic euxinic contractions drove manganese(II) oxidation and mineralization, shaping molybdenum cycling. This study highlights essential manganese(II) oxidation for manganese carbonate mineralization and offers new insights into molybdenum geochemistry and ancient ocean oxygenation events.

Nitrogen isotopes reveal high NOx emissions from arid agricultural soils in the Salton Sea Air Basin

Air quality management commonly aims to mitigate nitrogen oxide (NOx) emissions from combustion, reducing ozone (O3) and particulate matter (PM) pollution. Despite such ongoing efforts, regulations have recently proven ineffective in rural areas like the Salton Sea Air Basin of Southern California, which routinely violates O3 and PM air quality standards. With over $2 billion in annual agricultural sales and low population density, air quality in the region is likely influenced by the year-round farming activity. We conducted a source apportionment of NOx (an important precursor to both O3 and PM) using nitrogen stable isotopes of ambient NO2, which revealed a significant contribution from soil-emitted NOx to the regional budget. The soil source strength was estimated based on the mean δ15N-NOx from each emission category in the California Air Resources Board’s NOx inventory. Our annual average soil emission estimate for the air basin was 11.4 ± 4 tons/d, representing ~ 30% of the extant NOx inventory, 10× larger than the state’s inventory for soil emissions. Unconstrained environmental factors such as nutrient availability, soil moisture, and temperature have a first-order impact on soil NOx production in this agriculturally intensive region, with fertilization and irrigation practices likely driving most of the emissions variability. Without spatially and temporally accurate data on fertilizer application rates and irrigation schedules, it is difficult to determine the direct impacts that these variations have on our observations. Nevertheless, comparative analysis with previous studies indicates that soil NOx emissions in the Imperial Valley are likely underrepresented in current inventories, highlighting the need for more detailed and localized observational data to constrain the sizeable and variable emissions from these arid, agricultural soils.

New bass on the block: Trophic interactions among invasive largemouth bass Micropterus salmoides and local sportfish.

Novel introductions of largemouth bass, Micropterus salmoides, often cause negative impacts on endemic populations of prey fishes and interspecific competitors. Although many studies have investigated trophic interactions between M. salmoides and smallmouth bass, Micropterus dolomieu, few have included chain pickerel, Esox niger, as a competitor despite similarities in their habitat use. We used stable isotope analysis to investigate the trophic ecology of a recently introduced population of M. salmoides in the Wolastoq|Saint John River. Specifically, we measured carbon (δ13C) and nitrogen (δ15N) isotopes to describe isotopic niches and infer resource use of introduced M. salmoides, M. dolomieu, E. niger, and native yellow perch, Perca flavescens, at various life stages. Our results showed that isotopic niche overlap occurred between M. salmoides and other study species, indicative of resource competition. However, resource use plasticity, as demonstrated by a wide variety of resources (marine, terrestrial, littoral, and pelagic) used by all study species, could potentially reduce interspecific competition. Our findings indicate that competition is highest between adult M. salmoides and E. niger, but the presence of a seasonal marine resource can provide important contributions to diets and potentially reduce competition. Further research should focus on monitoring of long-term trends to identify the dynamics of all study species as M. salmoides populations become further established and dispersed.

Tracing the origin of volatiles on Earth using nitrogen isotope ratios in iron meteorites

Understanding the relationships between the nitrogen (N) isotope ratios of early solar system planetesimals and terrestrial reservoirs is crucial for tracing the origin of volatiles on Earth. The Earth primarily grew from planetesimals and planetary embryos that accreted rapidly (within ∼1–2 Ma after CAIs) in the inner solar system, also known as the non-carbonaceous (NC) reservoir. Magmatic iron meteorites, which sample the metallic cores of the earliest solar system planetesimals, have emerged as a promising proxy in this exercise. NC irons are distinctly 15N-poor compared to their CC (carbonaceous or outer solar system) counterparts. However, the utility of this proxy is limited by the lack of knowledge of N isotope fractionation during core crystallization. Using high pressure-high temperature experiments, we show that equilibrium N isotopic fractionation between solid and liquid metal (Δ15Nsolid–liquid = δ15Nsolid − δ15Nliquid) is limited (≤1.2 ‰) under conditions relevant for core crystallization. This, combined with the siderophile character of N and limited equilibrium N isotope fractionation during core-mantle differentiation, suggests that the δ15N values of iron meteorites accurately represent the N isotopic composition of their parent bodies. Unlike the variation in the N isotope ratios of NC and CC chondrites, which can be attributed to the effects of parent-body processes acting on organic precursors, the 15N-poor nature of NC irons relative to CC irons likely offers the most definitive evidence for the distinct N isotopic compositions of the earliest inner and outer solar system planetesimals. The N isotopic composition of Earth’s primordial mantle (δ15N = <−40 ‰) suggests that it retains the memory of the early accretion of 15N-poor NC iron meteorite parent body-like planetesimals. The early accreted 15N-poor nitrogen may be stored in the deep mantle, segregated into the core, or lost to space during atmospheric loss caused by impacts. This signature was overprinted by the subsequent accretion and admixing of CC materials, which is reflected in the relatively 15N-rich nature of Earth’s atmosphere (δ15N = 0) and convecting mantle (δ15N = −5 ‰).

Source apportionment of organic carbon and black carbon in the surface sediments of the Pearl River Estuary and its adjacent South China Sea: insight from stable carbon and nitrogen isotopes

Coastal estuaries and adjacent continental shelf seas constitute vital global carbon reservoirs, and the sources and transformations of organic carbon in these regions are crucial to global biogeochemical cycles and climate change. This study investigated the total organic carbon (TOC), total nitrogen (TN), black carbon (BC), and their stable carbon and nitrogen isotopes (δ15NTN, δ13CTOC, δ13CBC) in the surface sediments of the Pearl River Estuary (PRE) and its adjacent northern South China Sea (NSCS) aiming to assess the impact of human activities on organic carbon dynamics in these areas. Results showed that the highest TOC concentrations occurred in the inner PRE due to intense human activities, and decreased seaward. The west side of the PRE exhibited higher TOC levels than the east side, which was attributed to differences in hydrodynamic processes and human activities. The westward flow of the Pearl River diluted water, which carried terrestrial organic matter inputs due to the influence of the Coriolis effect and intense local human activities, was a primary contributor to higher TOC levels on the west side (terrestrial source). In contrast, increased productivity and intensive mariculture activities on the east side predominated as sources of organic matter (marine source). Similar to the TOC, BC and TN sources were mainly influenced by human activities. δ15NTN distribution shows that TN in the east side of PRE mainly originated from industrial wastewater input from the Pearl River, while in the east side TN was mainly from domestic sewage discharge. Additionally, BC sources have shifted from primarily biomass combustion in the 1990s to fossil fuel emissions presently. Isotopic analysis revealed that over 70% of BC originated from fossil fuel inputs and C3 plant combustion, highlighting the significant influence of human activities in the PRE and adjacent NSCS, and underscoring the need for effective management and protection of the eco-environment in these regions.

Just Hitching a Ride: Stable Isotopes Reveal Non-Feeding Behaviour of Anisakis simplex Within Its Host Fish.

Anisakis simplex larvae, commonly found in marine fish, cause anisakiasis in humans, resulting in gastric to gastro-allergic symptoms. Despite known health risks, the impact of Anisakidae larvae on fish hosts is less understood. This study aimed to investigate this interaction by assessing the feeding strategy of A. simplex. Anisakis larvae were isolated from North Sea Merluccius merluccius tissues (stomach, body cavity, liver and muscle) and were analysed for carbon (δ13C) and nitrogen (δ15N) isotope values. Significant differences in δ13C values were found among host tissues, with the liver differing from muscle and stomach tissues. In contrast, no differences were noted for the associated parasites. Additionally, δ15N values indicated that the host occupied a significantly higher relative trophic position than its parasite. This suggests a lack of direct nutrient transfer from host to parasite, as the parasite would typically exhibit higher stable isotope values than the tissue they feed on. Therefore, A. simplex's stable isotope values might reflect those of its previous host (crustacean and/or small fish), providing insights into diet and movement of the paratenic M. merluccius host. Further research is needed to confirm these findings across different fish species and to explore A. simplex as a proxy for trophic ecology.

Perturbations in a pelagic food web during the NE pacific large marine heatwave and persistent harmful diatom blooms

Unprecedented warm ocean conditions, driven by the Large Marine Heatwave (LMH) and the 2015–16 El Niño in the Northeast Pacific favored pervasive toxigenic Pseudo-nitzschia spp. blooms that caused widespread ecological impacts, but little is known about the magnitude to which marine food webs were altered. Here, we assessed the trophic transfer of domoic acid (DA; a neurotoxin) and changes in trophic position from multiple key species during the peak of the LMH and El Niño in 2015 in comparison with 2018, a reference non-anomalous warm year. DA and amino acid nitrogen isotopes (δ15N AAs) were quantified using liquid and gas chromatography mass spectrometry, respectively. Our integrative approach revealed extremely high levels of DA in anchovy viscera (>3000 μg/g) with contrasting baseline values (δ15N Phe) for southern California fish. These results together with data from northern CA revealed an unforeseen latitudinal isotopic variation in key DA vectors along California, possibly driven by anomalous restructuring of water masses. At the regional level, the observed cross-shore differences in baseline isotope values and DA toxicity suggest distinct pathways for DA trophic transfer for nearshore vs. offshore sites. Given the high levels of environmental disturbance during the LMH and persistence of toxigenic P. australis blooms, our resultant higher trophic position proxies in 2015 compared to 2018 were particularly unexpected. Such results highlight complex trophic interactions, where the trophic status of some species increased while others decreased in response to changes in net primary productivity, and biodiversity, and abundance of forage species. Our study demonstrates the use of δ15N AAs to identify pathways of N and DA trophic transfer and to quantify shifts in animal trophic position, a critical facet of understanding the response of food webs to climate change and DA production.

Isotopic analysis of modern sorghum and finger millet from different altitudes in Ethiopia: implications for ancient farming practices

C4 crops such as sorghum (Sorghum bicolor) and finger millet (Eleusine coracana) have played a significant role in the economic livelihood in arid and semi-arid zones of tropical and sub-tropical Africa since prehistoric times. However, to date, our knowledge of their past management practices is limited. Stable isotope analysis of archaeobotanical remains has been recognized as a valuable tool for reconstructing past agricultural practices, e.g. water management, and fertilization. Nonetheless, our limited understanding of the isotopic variability of C4 plants calls for further research on modern plant before application to archaeobotanical remains. In this paper, we aim to enhance our understanding of modern C4 botanical remains' isotopic variability by analyzing sorghum and finger millet plants. These crops were cultivated according to traditional local practices and collected from ten villages located in the Konso Zone (South Ethiopia) and Tigray Regional State (North Ethiopia), where they are among the daily ingredients for food, and traditional alcoholic and non-alcoholic drinks. We analyzed carbon and nitrogen stable isotopes of seeds and biosilica content in chaff, as it has been suggested that a relationship can exist between silicon and C:N. Carbon isotope values show significant variability, positively correlated with altitude. By demonstrating the sensitivity of C4 grain carbon stable isotope to altitude variations, which are likely connected to water availability, this study offers invaluable insights for the accurate assessment of isotopic values derived from ancient C4 crops. The absence of significant correlations with δ15N suggests that nitrogen isotope values may be less effective for understanding environmental variations in this kind of context. This highlights the limitations of nitrogen isotope data for interpreting ancient agricultural practices and underscores the importance of relying more on carbon isotopes for insights related to environmental conditions and altitude. Furthermore, we confirm that the amount of assimilated carbon may depend also on the biosilica content, which is in turn modulated by environmental parameters such as water availability or soil silicon levels.

Isotopic evidence of diet breadth hunter-gatherers changes during the Holocene in the Central Pampean Dunefields (Argentina, South America).

Based on the analysis of stable carbon and nitrogen isotopes of bone collagen, stable carbon isotopes of bone apatite and an extensive AMS dating series (~10,000-299 years cal BP), the human paleodiets of 34 individuals from the Central Pampean Dunefields (Argentina, South America) are evaluated. These data are interpreted from the isotopic ecology of animals with archaeofaunal evidence of consumption and isotopic models of human diet. Multivariate carbon and nitrogen stable isotope model and Bayesian stable isotope ellipses were used to interpret human diets. Analysis of isotopic values indicates intake of enriched lipids and/or carbohydrates in relation to the proteins consumed throughout the Holocene. The isotopic values of Middle Holocene humans in relation to the values of exploited resources point out that individuals obtained protein mainly from guanaco. Subsequently, there was an increase in the human breadth diet during the Late Holocene, with a greater relevance of small prey of high trophic levels and vegetables. This contrasts with zooarchaeological information indicating generalist human diets during the Middle Holocene and specialized human diets in guanaco during the Late Holocene. It is proposed that during the Middle Holocene arid period, the combination of low human population density and high residential mobility in wide foraging ranges allowed the guanaco to be the main source of protein. During the Late Holocene humid period, there was an increase in human population density and a decrease in residential mobility, which caused greater pressure on foraging territories and increased dietary breadth.