Nitrogen Isotopic Composition Research Articles

Climatic controls on stable carbon and nitrogen isotope compositions of temperate grasslands in northern China

The natural abundances of stable carbon (C) and nitrogen (N) isotopes (δ13C and δ15N) are extensively used to indicate the C and N biogeochemical cycles at large spatial scales. However, the spatial patterns of δ13C and δ15N in plant-soil systems of grasslands in northern China and their main driving factors across regional climatic gradient are still not well understood. We measured plant and soil δ13C and δ15N compositions as well as their associated environmental factors across 2000 km climatic gradient (-0.2 to 9 °C; 152 to 502 mm) in grasslands of northern China. The soil δ13C and δ15N values in surface were lower than those in bottom for temperate typical steppe but had no significant differences for temperate meadow steppe and temperate desert steppe. Soil δ13C values declined with increasing soil organic carbon (SOC) but increased as mean annual temperature (MAT). These changes were attributed to the microbial decomposition rate. The δ15N values in soil and plant were negatively correlated with MAT and mean annual precipitation (MAP), which were mainly related to the low soil organic matter mineralization rate and the shift of dominant species from C4 to C3. Our results indicate the spatial patterns and different influencing factors on δ13C and δ15N values along the climatic gradient in grasslands of northern China. The findings will provide scientific references for future research on the C and N biogeochemical cycles of temperate grasslands.

The isotopic compositions of hexamine solid fuel tablets used to manufacture hexamethylene triperoxide diamine (HMTD) explosive

Hexamine, derived from solid fuel tablets, is a potential source for a number of home-made explosives including the primary high explosive hexamethylene triperoxide diamine (HMTD). Therefore, a means to characterise hexamine samples and to link HMTD with precursor hexamine may provide investigative intelligence to counter-terrorism agencies.We report the hydrogen, carbon and nitrogen isotopic compositions of hexamine isolated from retail samples of solid fuel tablets. Hydrogen isotopic compositions ranged from –123.0 to +172.6‰, carbon isotopic compositions from –47.1 to –27.6‰ and nitrogen isotopic compositions from –3.1 to +0.3‰. Despite within- and between-tablet inhomogeneity, a combination of these data could be considered characteristic of specific brands or manufacturers.Ten samples of hexamine were each used to synthesize four batches of HMTD using two isotopically distinct sources of hydrogen peroxide. The δ13C and δ15N compositions of the HMTD ranged from –48.8 to –31.5‰ for carbon and from +13.7 to +17.8‰ for nitrogen. δ2H compositions across all batches of HMTD was much wider than previously reported; –109.3 to +196.6‰.The changes in carbon and nitrogen isotopic compositions, progressing from hexamine to HMTD, could be explained by a reaction mechanism involving the decomposition of hexamine to methylimine and formaldehyde. Data also supported a mechanism whereby the hydrogen atoms of HMTD were derived from hexamine and not from other reagents.Based on the relationships Δ2HHEXAMINE-HMTD and Δ13CHEXAMINE-HMTD, a rule-of-thumb was proposed to identify possible hexamine precursors of HMTD.

Nitrogen Isotopes of Sinking Particles Reveal the Seasonal Transition of the Nitrogen Source for Phytoplankton

AbstractIn the high‐productivity subarctic ocean, phytoplankton growth is assumed to rely mainly on nitrate, based on snapshot observations conducted in spring or summer. However, the year‐round utilization of nitrate and ammonium by phytoplankton remains unexplored. Here, we show the seasonal transition of the dominant nitrogen source for phytoplankton by using the nitrogen isotopic composition (δ15N) of nitrate, ammonium, and sinking particles in the northwestern North Pacific. To decouple the combined effects of nitrogen sources for phytoplankton and subsequent trophic transfers in δ15N of sinking particles, we used compound‐specific δ15N analysis of amino acids (δ15NAA) in sinking particles. The seasonal change in δ15NAA revealed that most of the seasonal variation in δ15N of sinking particles arose from changes in the availability of nitrogenous nutrients in the euphotic layer. The δ15N of sinking particles suggested that the dominant nitrogen source for phytoplankton switches from nitrate to ammonium in autumn.

Is fertilization the dominant source of ammonia in the urban atmosphere?

It was previously believed that ammonia (NH3) has a short residence time in the atmosphere and cannot be transported far from its sources. In late March, however, this study observed a severe NH3 episode in urban Beijing when fertilizer was intensively applied on the North China Plain, with the highest hourly concentrations of 66.9 μg m-3 throughout the year. The stable nitrogen isotopic composition of NH3 (δ15N-NH3) during this episode (-37.0 to -20.0‰) fell in the range of endmembers of fertilizer and livestock, suggesting the long-range transport of NH3 from agricultural to urban regions. Based on a Bayesian isotope mixing model, the contribution of agriculture (fertilization) to urban NH3 concentrations was apportioned as 43.5% (26.0%) on polluted days. However, these contributions were reduced to 29.1% (12.8%) when nitrogen isotope fractionation between NH3 and ammonium was considered. In contrast to the limited contribution of agricultural sources, we found that nonagricultural emissions, particularly vehicles, dominate the source of NH3 in urban Beijing, even during the fertilization period. This finding indicated that nonagricultural sources should be considered when designing a control strategy for NH3 to reduce haze pollution in the urban atmosphere.

Pig management in the Neolithic Near East and East Asia clarified with isotope analyses of bulk collagen and amino acids

The chemical analysis of animal bones from ancient sites has become a common approach in archeological research investigating animal utilization and domestication by past humans. Although several chemical indicators have been used to determine pig management practices in ancient societies, one indicator that can clarify human-animal relationships in the early stages of domestication is the change in the animal’s diet from its wild diet, which can be detected using isotope analysis of its bones. Omnivores, such as boars, are assumed to have shared foods with humans as their interaction increased, and a shift in the isotopic (carbon and nitrogen) compositions of their bone collagen toward humans are considered evidence of domestication. This approach has found evidence of early-stage pig management with human leftovers and feces in prehistoric East Asia, including in Neolithic China, Korea and Japan. However, in the Near East, one of the origins of animal domestication, even individual animals considered to be domesticated pigs according to zooarcheological data (such as morphological characteristics and mortality patterns) display isotopic compositions of bulk collagen that differ from those of humans but are close to those of herbivores. This result indicates that these pigs were fed special foods, such as legumes, rather than human leftovers or feces. However, the carbon and nitrogen isotopic compositions of the bulk collagen of herbivores found at the same sites showed huge variations, so the interpretation of the pigs’ diet is consequently unclear. In this study, a compound-specific nitrogen isotope analysis was used to clarify the pig diet and management strategies unique to the Neolithic Near East, Turkey and Syria, together with a carbon and nitrogen isotope analysis of bulk collagen. This study examines the diversity of pig management techniques in early agricultural societies and their relationship with the availability of other domestic animals and farming practices.

Climatic control effect on the soil nitrogen isotopic composition in Alisols across the physiographic regions of Pernambuco State, Northeast Brazil

Soil nitrogen dynamics in terrestrial ecosystems can be evaluated by analyzing the natural abundances of N isotope ratio mass spectrometry (δ15N) because δ15N integrates decades of organic matter transformations in the soil. On a large scale, the δ15N of soil organic matter across climate gradients may provide critical insights into understanding regional patterns of N cycling. However, the mechanisms that control N cycling in some tropical regions still present critical gaps, particularly in dry ecosystems. We evaluated the variation of soil δ15N in Alisols along the climatic gradient of three physiographic regions in Northeast Brazil: Zona da Mata (humid, rainfall well distributed throughout the year), Agreste (subhumid, rainfall concentrated in 5–7 months), and Sertão (semiarid, rainfall in highly intense events, concentrated over 3–5 months). Soil samples were collected at the 0–20 cm depth layer and analyzed for physical and chemical characteristics, including soil δ15N, by mass spectrometry. A linear model with physical biological, chemical, and climatic variables was generated to explain the spatial distribution of the soil δ15N. The map modeled values δ15N for Pernambuco State was produced using all observed values and the best-performing explicit spatial predictive variables in the model selection – pH, clay content, mean temperature, mean precipitation, and potential of evapotranspiration. Soil δ15N was positively related to clay content and negatively associated with the pH, temperature, rain, and evapotranspiration, expressing differences in nitrogen dynamics along the climatic gradient. In the Sertão, the low and erratic rainfall combined with a neutral pH and high temperature provide adequate conditions for nitrogen transformations and cause high soil δ15N.

New Constraints on Assemblage‐Driven Variation in the Relationship Amongst Diatom‐Bound, Biomass, and Nitrate Nitrogen Isotope Values

AbstractTracking variations in the surface ocean supply and demand of nitrate, a key marine nutrient, can help constrain the contribution of biological production in driving past climate shifts. The nitrogen isotopic composition (as δ15N) of organic matter in marine sediments is a proxy for surface ocean nitrate supply and demand over time, but it may be subject to alteration during sinking and burial. The isotopic composition of nitrogen occluded in the opal shells, or frustules, of diatoms (δ15NDB) is protected and is, therefore, a potentially more robust tracer of nitrate use in the past. Here, we show that δ15NDB in Southern Ocean growout cultures of natural communities does not depend on species composition. We found that the εDB (= biomass δ15N–δ15NDB) of the community growouts was −4.8 ± 0.8‰, more than 10‰ different from previous monospecific growouts, but statistically indistinguishable from previous Southern Ocean and North Pacific surface ocean observations. The two community growouts, seeded with populations from ∼66° to ∼61°S, had distinct community compositions, but indistinguishable εDB, suggesting that species composition does not primarily set δ15NDB values, at least in Antarctic and Polar Frontal Zones of the Southern Ocean. Our results demonstrate that under nitrate‐replete conditions, δ15NDB values of frustules sinking from the surface ocean robustly track surface ocean nitrate δ15N values, and therefore nitrate supply and demand.

Laboratory Assessment of the Impact of Chemical Oxidation, Mineral Dissolution, and Heating on the Nitrogen Isotopic Composition of Fossil‐Bound Organic Matter

AbstractFossil‐bound organic material holds great potential for the reconstruction of past changes in nitrogen (N) cycling. Here, with a series of laboratory experiments, we assess the potential effect of oxidative degradation, fossil dissolution, and thermal alteration on the fossil‐bound N isotopic composition of different fossil types, including deep and shallow water scleractinian corals, foraminifera, diatoms and tooth enamel. Our experiments show that exposure to different oxidizing reagents does not significantly affect the N isotopic composition or N content of any of the fossil types analyzed, demonstrating that organic matter is well protected from changes in the surrounding environment by the mineral matrix. In addition, we show that partial dissolution (of up to 70%–90%) of fossil aragonite, calcite, opal, or enamel matrixes has a negligible effect on the N isotopic composition and N content of the fossils. These results suggest that the isotopic composition of fossil‐bound organic material is relatively uniform, and also that N exposed during dissolution is lost without significant isotopic discrimination. Finally, our heating experiments show negligible changes in the N isotopic composition and N content of all fossil types at 100°C. At 200°C and hotter, any N loss and associated nitrogen isotope changes appear to be directly linked to the sensitivity of the mineral matrix to thermal stress, which depends on the biomineral type. These results suggest that, so long as high temperature does not compromise the mineral structure, the biomineral matrix acts as a closed system with respect to N, and the N isotopic composition of the fossil remains unchanged.

Non-agricultural source dominates the ammonium aerosol in the largest city of South China based on the vertical δ15N measurements

Ammonia (NH3) is the most prevalent alkaline gas in the atmosphere and plays a critical role in air pollution and public health. However, scientific debate remains over whether agricultural emissions (e.g., livestock and fertilizer application) dominate NH3 in urban atmosphere in China, which is one of the largest NH3 emitters in the world. In this study, we first simultaneously collected the fine atmospheric particles (PM2.5) at two heights (ground and 488 m) using the atmospheric observatories in Canton Tower, Guangzhou city, China for the measurements of stable nitrogen isotope composition in ammonium (δ15N-NH4+). Our results showed that the average δ15N-NH4+ value at the ground and the 488 m observatory were 16.9 ‰ and 3.8 ‰, respectively, implying that NH4+ aerosols between the two heights probably have different sources. Moreover, we found that the δ15N-NH4+ value would sharply decrease to −16.7 ‰ when the air masses came from western Guangzhou, where the urbanization is limited compared to other surrounding areas. The Bayesian mixing model indicated that NH4+ aerosol at the ground observatory was mainly derived from non-agricultural activities (76 %, e.g., vehicular exhaust), with the rest from agricultural sources (24 %). As for the 488 m observatory, the contribution of non-agricultural sources was 53 %, which is lower than the ground observatory. This is expected as the lower air receives more impacts from the local urban emission. However, the current “bottom-up” emission inventory illustrates that only ~20 % NH3 in Guangzhou is associated with non-agricultural emissions, which is significantly lower than our δ15N-based results. Overall, our findings strongly imply that non-agricultural sources dominate the urban NH3 in Guangzhou or maybe in adjacent cities of the Pearl River Delta region as well, suggesting that the emission inventory of NH3 in this region probably is urgently needed to be revisited in future studies.

Compound specific isotope evidence points to use of freshwater resources as weaning food in Middle Neolithic Paris Basin

ObjectivesA clear understanding of past weaning practices can provide invaluable insights into social issues such as infant care, fertility rate, and demographic patterns in past societies. This study presents the first archeological research employing compound specific isotope analysis (CSIA) for the reconstruction of past weaning practices.MethodsWeaning practices of two Middle Neolithic communities in the Paris Basin region: Balloy (BLR) and Vignely (VPB), are evaluated by combining previously published bone collagen stable carbon, nitrogen, and sulfur (n = 66) isotope analysis with new compound specific carbon and nitrogen isotope compositions of bone collagen (n = 10).ResultsOur results demonstrate that the diets of individuals from BLR and VPB likely incorporated freshwater resources. The signals of freshwater resources consumption are even stronger among subadults, suggesting that freshwater resources were used as weaning food at these sites.ConclusionsThe implications of our result are threefold. Currently many CSIA studies in archeology only involve either carbon or nitrogen. Our data shows that it is important to conduct CSIA on both carbon and nitrogen for a more integrated picture. Secondly, our data demonstrates that the use of a protein‐based weaning food—instead of a starch‐based weaning food (such as cereal gruel)—was likely more prevalent among the Middle Neolithic communities in the Paris Basin Region than previously thought. The finding thus prompts a rethinking of the role of protein‐based weaning food in other archeological contexts. Lastly, the common assumption that weaning foods and adult diets share similar isotopic compositions can be problematic, as the use of protein‐based, high trophic‐level weaning foods can skew the δ 15N weaning curve and produce an erroneously late estimation for weaning ages.

The variation and trends of nitrogen cycling and nitrogen isotope composition in tree rings: the potential for fingerprinting climate extremes and bushfires

PurposeClimate extremes, such as droughts and floods, have become intensified and more frequent due to intensifying climate change. Increased atmospheric carbon dioxide (CO2) and warming-induced water limitation, as well as climate extremes, may alter carbon (C) and nitrogen (N) cycling in forest ecosystems. This provides a brief review of stable nitrogen isotopic composition (δ15N) in tree ring in relation to climate extremes and bushfires in context of N availability and losses in forest ecosystems.Material and methodsTree rings were extracted from four Pinus sylvestris and four Larix gmelinii sample trees, located in a boreal plantation forest of Mohe City, Heilongjiang Province, China. Tree rings were measured to obtain mean annual basal area increment (BAI), while tree ring δ15N and total N concentrations were measured on mass spectrometer at 3-year intervals. The tree ring δ15N data were related to possible climate extremes and bushfires. A brief review of the relevant literature was also undertaken to support our preliminary research findings.Results and discussionGlobally, increasing atmospheric CO2 concentration and water limitations have led to a warmer-drier climate. This has also been associated with increases of climate extremes such as drought and floods as well as bushfires. These extremes have been recorded with detrimental effects on plant and soil structures within forest ecosystems and play an important role in regulating N availability and losses in forest ecosystems. Studies of N deposition within forest ecosystems using soil and plant δ15N also showed that N losses under various climate extremes can occur through direct changes in N cycling, such as increasing soil nitrification and denitrification or leaching. It is highlighted that tree rings δ15N has the potential to fingerprint the intensity and frequency of climate extremes and bushfires in the forest ecosystems, but more such tree ring δ15N research needs to be done in diversified forest ecosystems to confirm the potential of using tree ring δ15N for quantifying the frequency and intensity of climate extremes and bushfires at both regional and global scale.ConclusionThe variation and trend of δ15N in the soil–plant-climate systems are closely linked to the N cycling in forest ecosystems, and tree ring δ15N has the great potential to fingerprint both intensity and frequency of climate extremes such as drought and floods as well as bushfires.

Integrative assessment of amino acid nitrogen isotopic composition in biological tissue samples determined by GC/C/IRMS, LC × EA/IRMS, and LC × GC/C/IRMS

AbstractCompound‐specific isotope analysis of nitrogen (δ15N) in amino acids (CSIA‐AA) has significantly contributed to environmental sciences such as anthropology, biogeochemistry, and ecology. Several methods exist for determining δ15N of amino acids (AAs). Although these methods have their own strength and weakness, they have not been intercalibrated yet, especially for biological samples with matrices. To address this issue, we systematically compared AA δ15N values among three methods using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS), preparative liquid chromatography (LC) separation followed by elemental analyzer/IRMS (LC × EA/IRMS), and LC separation followed by GC/C/IRMS (LC × GC/C/IRMS). The δ15N values of glutamic acid (δ15NGlu) and phenylalanine (δ15NPhe) in fish muscle, two crucial AAs for estimating the trophic positions (TPs) of organisms, were compared among methods. Although a significant difference in fish muscle δ15NGlu values was found among the three analytical methods, their δ15NGlu and δ15NPhe values were fairly consistent between all pairs of methods (n = 8, R2 = 0.9968 for GC/C/IRMS vs. LC × GC/C/IRMS; 0.9936 for LC × EA/IRMS vs. LC × GC/C/IRMS; and 0.9912 for GC/C/IRMS vs. LC × EA/IRMS), which resulted in similar TP estimates among the methods. Thus, the results provide empirical validation that the CSIA‐AA is comparable among different methods in interdisciplinary research fields. We also highlighted some critical features of each of the three analytical methods that can be used as a guideline for future CSIA‐AA research.

Anthropogenic eutrophication of Lake Titicaca (Bolivia) revealed by carbon and nitrogen stable isotopes fingerprinting

Cultural eutrophication is the leading cause of water quality degradation worldwide. The traditional monitoring of eutrophication is time-consuming and not integrative in space and time. Here, we examined the use of carbon (δ13C) and nitrogen (δ15N) isotopic composition to track the degree of eutrophication in a bay of Lake Titicaca impacted by anthropogenic (urban, industrial and agricultural wastewater) discharges. Our results show increasing δ13C and decreasing δ15N signatures in macrophytes and suspended particulate matter with distance to the wastewater source. In contrast to δ15N and δ13C signatures, in-between aquatic plants distributed along the slope were not only affected by anthropogenic discharges but also by the pathway of carbon uptake, i.e., atmospheric (emerged) vs aquatic (submerged). A binary mixing model elaborated from pristine and anthropogenic isotope end-members allowed the assessment of anthropogenically derived C and N incorporation in macrophytes with distance to the source. Higher anthropogenic contribution was observed during the wet season, attributed to enhanced wastewater discharges and leaching of agricultural areas. For both seasons, eutrophication was however found naturally attenuated within 6 to 8 km from the wastewater source. Here, we confirm that carbon and nitrogen stable isotopes are simple, integrative and time-saving tools to evaluate the degree of eutrophication (seasonally or annually) in anthropogenically impacted aquatic ecosystems.

On the provenance of GEMS, a quarter century post discovery

The provenance of GEMS (glass with embedded metal and sulfides) in cometary type interplanetary dust particles is investigated using analytical scanning transmission electron microscopy and secondary ion mass spectrometry. We review the current state of knowledge and closely examine the densities, elemental compositions and distributions, iron oxidation states, and isotopic compositions of a subset of GEMS in chondritic porous interplanetary dust. We find that GEMS are underdense with estimated densities that are 35–65% of compositionally equivalent crystalline aggregates. GEMS low densities result in a lower contribution to the bulk compositions of IDPs than has been assumed based on their volume fraction. We also find that element/Si ratios, assumed to be primary (indigenous), are instead perturbed by contamination and secondary alteration, including pulse heating during atmospheric entry. Fe in pyrrhotite inclusions was oxidized and Mg, S, Ca, and Fe were depleted relative to lithophile Al and Si, resulting in reduction in element/Si ratios. Because they trap outgassing elements, Fe-rich oxide rims that formed on the surface of GEMS are serendipitous “witness plates” to the changes in composition that accompany atmospheric entry. As a result of alteration, GEMS elemental compositions cannot reliably inform about their provenance. Except for highly anomalous oxygen isotope ratios measured in some large GEMS grains that indicate a contribution from circumstellar dust, oxygen isotope compositions are generally poor indicators of provenance. Prior work indicates that most GEMS fall close to the terrestrial oxygen isotope composition, which, however, does not exclude a presolar interstellar origin. Nitrogen isotopic compositions are more diagnostic. Elevated 15N/14N ratios indicate that GEMS accreted in conjunction with formation of organic matter by ion–molecule reactions in a cold (<50 K) presolar environment like the extreme outer nebula or interstellar medium. Considering all observations, we conclude that GEMS are most likely processed interstellar silicates.

The synthesis of MDA from helional and characterisation by isotope ratio mass spectrometry

Presented here is an investigation into the stable isotopic ratios of 3,4-methylenedioxyamphetamine (MDA) prepared from the alternative precursor helional. Two methods for the synthesis of MDA were investigated, both utilising hydroxylamine as the nitrogen source. Recent publications found both helional and hydroxylamine with isotopic compositions significantly different to traditional precursors and nitrogen sources. While minimal fractionation was observed in carbon isotopic compositions, apparent fractionation occurred to hydrogen, nitrogen and oxygen isotopic compositions during the synthesis of MDA. Fractionation observed in δ15N were explained by the reaction conditions during the addition of hydroxylamine. The fractionation observed in δ18O was consistent with the replacement and loss of an oxygen atom during the synthesis of the amide intermediate and MDA. A brief investigation into isotopic fractionation during MDA hydrogen chloride (HCl) salt precipitation was also conducted, and additional fractionation may be expected in both δ2H and δ15N during the process, consistent with the proposed mechanism. These results suggest that tactical intelligence can be gained from the batch-to-batch variations to isotopic composition of MDA during the synthesis from helional.

Dual isotopes of nitrite in the Amundsen Sea in summer

Nitrite (NO2−) is a key intermediate in the nitrogen (N) cycle, and its transformation is accomplished by microbial communities. However, due to few studies on the nitrite cycle, a clear assessment of the contribution to the marine biogeochemical cycle is missing. Here, we present data on nitrogen and oxygen isotopic composition of NO2− in the Amundsen Sea in summer, and explore the biogeochemical processes that influence the NO2− cycle. Extremely low δ15NNO2 and abnormally high δ18ONO2 were found in the upper waters of the Amundsen Sea, with δ15NNO2 as low as −58.4 ‰ and δ18ONO2 as high as 44.4 ‰. Enzymatic isotopic exchange reactions between nitrate and nitrite have been proposed to be responsible for these isotopic anomalies. The mirror-symmetrical variation between δ15NNO2 and δ18ONO2 suggests that the isotopic fractionation effects of nitrogen and oxygen are opposite in isotope exchange reactions. Dual isotopes of nitrite indicate that ammonia oxidation is the main source of nitrite, thus nitrification plays an important role in the formation of primary nitrite maximum in the upper Amundsen Sea. The nitrogen and oxygen isotopic compositions of nitrite provide support for clarifying multiple processes of marine nitrogen cycle.

Sources and Formation of Atmospheric Nitrate Over China–Indochina Peninsula in Spring: A Perspective From Oxygen and Nitrogen Isotopic Compositions Based on Passive Air Samplers

The formation processes and potential sources of particulate nitrate can be revealed by nitrogen (δ15N-NO3−) and oxygen (δ18O-NO3−) isotopes; however, the linkage and comparative information over a large scale is limited. In this work, the feasibility of using quartz wool disk passive air samplers (Pas-QW) to identify and quantify the nitrate concentrations and their isotopic compositions was demonstrated. The results of a simultaneous sampling campaign from March to June showed that the NO3− concentration was largely attributed to the development of the regional economies. The regional distribution of δ15N-NO3− values was due to the source changes. The decreasing trend of δ18O-NO3− values with latitude from south to north was mainly a combination of oxygen isotopic fractionation of the oxidant induced by natural factors and anthropogenic changes in O3 concentrations. Coal combustion (CC) and mobile sources (MS) have a significant contribution to NOx in the typical urban agglomerations, while the high contribution from biomass burning (BB) and biogenic soil emission (BS) was mainly in areas with high natural productivity and intensive agricultural activities. By allowing simultaneous monitoring at multiple sites and over extended periods, passive sampling complements existing techniques for studying nitrate aerosol, and the results can provide a reference for the spatial distribution of its sources and formation in the China–Indochina Peninsula (CICP).

Epigenetic and Phenotypic Responses to Experimental Climate Change of Native and Invasive Carpobrotus edulis.

Despite the recent discoveries on how DNA methylation could help plants to adapt to changing environments, the relationship between epigenetics and climate change or invasion in new areas is still poorly known. Here, we investigated, through a field experiment, how the new expected climate scenarios for Southern Europe, i.e., increased temperature and decreased rainfall, might affect global DNA methylation in relation to phenotypic variation in individuals of clonal plant, Carpobrotus edulis, from its native (Southern African) and invaded (northwestern Iberian Peninsula) area. Our results showed that changes in temperature and rainfall induced phenotypic but not global DNA methylation differences among plants, and the climatic effects were similar for plants coming from the native or invaded areas. The individuals from the Iberian Peninsula showed higher levels of global methylation than their native counterparts from South Africa. We also observed differences between natives and invasive phenotypes in traits related to the pattern of biomass partitioning and to the strategies for water uptake and use and found an epigenetic contribution to phenotypic changes in some leaf traits, especially on the nitrogen isotopic composition. We conclude that the increased temperature and decreased rainfall projected for Southern Europe during the course of the twenty-first century may foster phenotypic changes in C. edulis, possibly endowing this species with a higher ability to successful cope the rapid environmental shifts. The epigenetic and phenotypic divergence that we observed between native and invasive plants suggests an intraspecific functional variation during the process of invasion. This result could indicate that phenotypic plasticity and global DNA methylation are related to the colonization of new habitats. Our findings reinforce the importance of epigenetic plasticity on rapid adaptation of invasive clonal plants.

Spatial Variation in Elemental and Isotopic Compositions of Carbon and Nitrogen in a Coastal Lagoon Reveals Natural and Anthropogenic Influences

Increased delivery of particulate organic matter (POM) to coastal lagoons has caused disturbance in nutrient cycling, water quality and aquatic biodiversity. Therefore, the major concern in coastal management is assessment of sources and pathways of POM in order to maintain ecosystem health. Elemental and isotopic of POM compositions are being increasingly used as useful markers for sources of POM in coastal ecosystems to obtain understanding of the nutrient sources and anthropogenic influences. In this study, variation in elemental and stable isotope compositions of carbon (C) and nitrogen (N) were measured in Cau Hai lagoon, Central Vietnam to characterize the possible sources of C and N. Variations in values of C/N ratios (8.17 ± 0.14) and 13C (-22.00‰ ± 0.13) indicated that POM was mainly of autochthonous origin due to high microalgae productivity. The values of 15N (3.83‰ ± 0.08) were likely inferred from potential input of POM from aquaculture practices. These results suggest that main sources of POM in the lagoon were derived from autochthonous microalgae and slightly anthropogenic impacts through aquaculture activities. Control POM load should be taken into account in maintaining water quality and biodiversity in the lagoon to inhibit microalgae biomass and shading due to nutrient enrichment.

Developing Nitrogen Isotopic Source Profiles of Atmospheric Ammonia for Source Apportionment of Ammonia in Urban Beijing

Atmospheric ammonia (NH3) is the key precursor in secondary particle formation, which is identified as the most abundant components of haze in Beijing in most cases. It is critical to understand the characteristics of NH3 from various emission sources and quantify each source contribution to NH3 in ambient atmosphere. Stable nitrogen (N) isotope composition (δ15N) is an effective tool to study NH3 source. However, this tool cannot be effectively applied in Beijing due to the lack of comprehensive N nitrogen isotope source profiles. Reliable source profiles are the basis of source apportionment of NH3 using the isotope mixing model. In this study, multiple NH3 source samples were collected at sites, representing six major NH3 source types in Beijing from 2017 to 2018 in four seasons. The δ15N values of 212 NH3 source samples were determined to build a local source profiles database of δ15N. NH3 from traffic source presents significantly higher δ15N values (−14.0 ± 5.4‰), distinguished from other sources. The δ15N values of other sources besides traffic were more depleted and did not clear differences (solid waste, sewage, human feces, fertilizer, and livestock for −33.6 ± 4.5‰, −34.1 ± 4.8‰, −32.2 ± 3.8‰, −35.0 ± 3.9‰, and −34.9 ± 4.4‰, respectively). These sources were classified into non-traffic source in this study. From March 2018 to March 2019, ambient NH3 samples were collected at an urban site in Beijing. With the newly developed source profiles in this study, the contribution of traffic and non-traffic sources to ambient NH3 in an urban site in Beijing was calculated using 15N isotope mass balance equations. Traffic and non-traffic sources contributed 8% and 92% to ambient NH3 in urban Beijing, respectively. The highest seasonal average contribution of traffic to ambient NH3 was found in winter (22%). Our results reveal the importance of traffic source and provide evidence for the need to control NH3 emission from traffic in urban Beijing in winter.