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Nitrogen isotope compositions (d15N) of sedimentary rocks are usually used to reconstruct the paleoenvironment and nitrogen (N) biogeochemical cycle. The d15N values of crude oils inherit the characteristics of relevant source rocks and can well reflect the information of hydrocarbon-forming organisms and environment in ancient water column. However, studies on the d15N of crude oils are limited due to the low N content. In this study, a new efficient method is applied to the marine oils from the Bashituo (BST) and Halahatang (HLHT) areas of the Tarim Basin to obtain the nitrogenous components (i.e., nonhydrocarbons and asphaltenes) for the achievement of N concentration. The carbon and nitrogen isotopes of these components and the biomarkers of oils were measured. The d15N values in asphaltenes (d15NAsp) are significantly heavier than those in nonhydrocarbons (d15NNSOs) in these oils, which are attributed to the potential directional N transfer and kinetic isotope fractionation during the thermal evolution of organic matters (OM). The d15NAsp values have significant correlations with OM origin associated parameters and weak correlations with environmental parameters, suggesting that the difference in d15NAsp values is mainly resulted from biological source rather than redox conditions. The d15NNSOs values have a closer relationship with the redox condition than biological characteristics, indicating that they have a good response to paleoenvironmental variation in the water column, which is not completely overprinted by the difference of OM origin. Different redox conditions give rise to distinct nitrogen cycles, resulting in various d15N values. Anammox occurs in the water column of the Early Cambrian dominated by physically stratified conditions with significant isotope fractionation, resulting in relatively heavier d15N of OM in the BST area. In the MiddleeLate Ordovician period, the limited suboxic zone leads to an insignificant positive bias of d15N caused by partial denitrification in the HLHT oils. The evaluation of d15N in nitrogenous fractions enables a more comprehensive reconstruction of N cycle for ancient oceans. [ABSTRACT FROM AUTHOR]

Abstract Gaseous ammonia (NH3) is a key precursor in the formation of PM2.5 in the atmosphere. To enhance the precision of identifying NH3 sources through isotopic techniques and alleviate urban air PM2.5 pollution, this paper reviews recent researches on the following aspects; methods for sampling and quantifying gaseous NH3 techniques for determining or estimating its nitrogen isotope ratios, the nitrogen isotope compositions and fractionations of NH3, in air and emitted from diverse sources, the isotopic compositions of NH4+ in atmospheric particulate matter and rainfall, as well as the source apportionment of atmospheric NH3. Several recommendations for future research are accordingly proposed. The minimum amount of samples should be determined before collecting air samples with passive method considering nitrogen isotope fractionation of NH3.It is necessary to clarify the nitrogen isotope compositions of ammonia from biomass combustion, natural soils, oceans, sewage plants, vegetation, and other potential sources. The nitrogen isotopic variation mechanism for ammonia from diverse sources needs to be further investigated. Both mass concentrations and isotopic compositions of gaseous NH3 and particulate NH4+ should be measured simultaneously with higher temporal resolution to explore the mechanism of nitrogen isotope fractionation during the formation of particulate NH4+. Additionally, exploring the isotopic fractionation of gaseous NH, under diverse meteorological conditions and air pollution status is recommended. [ABSTRACT FROM AUTHOR]

The Nanhua Basin of South China recorded complete Cryogenian stratigraphic sequence from the Sturtian Glaciation (~717-660 Ma) to the Marinoan Glaciation (~?654-635 Ma). The interglacial Datangpo Fm in the Nanhua Basin is divided into two members, and the first member consists of the Mn-carbonate unit and the overlying black shale unit, containing a series of large and superlarge manganese deposits. The metallogenic process of manganese deposits is not clear, and the Mn-carbonates formed through the precursor of Mn-oxide/oxyhydroxide reduction or directly precipitated from an anoxic water column. Moreover, the redox conditions in the deep Nanhua Basin during the precipitation of manganese deposits are also controversial. In this study, the high-resolution nitrogen contents (TN), isotope compositions, carbon isotope compositions of organic and inorganic matter from the first member of the Datangpo Fm are analyzed. The δ15N values of the Mn-carbonate unit (+1.53‰ to +5.26‰, mean +3.36‰) are higher than those of the overlying black shale unit (-3.74‰ to +3.54‰, mean +0.89‰). The Mn contents show a negative relationship with TN but a positive relationship with δ15N in the Mn-carbonate unit, implying that the formation of Mn-carbonates is related to redox variations. The relatively higher δ15N values in the Mn-carbonate unit indicated oxic conditions, and NH4+ can be released and partially oxidized during the mineralization of organic matter, resulting in the residual 15N-enriched NH4+ being transferred into clay minerals. Meanwhile, the lower δ15N values in the black shale unit indicated anoxic conditions, which recorded primary N isotope signals. The Mn-carbonate unit is characterized by negative δ13Ccarb values (-11.17‰ to -5.22‰, mean -8.30‰), which show a positive relationship with δ13Corg, but a negative relationship with Mn contents, implying that the negative δ13Ccarb excursions were related to the organic matter degradation during Mn-carbonate formation. The findings of this study indicated that the metallogenesis of manganese deposits in the Cryogenian Nanhua Basin was constrained mainly by the oxic interval in the deep basin. The nitrogen and carbon cycling process can provide new insights into geochemical cycling after the Sturtian Glaciation. [ABSTRACT FROM AUTHOR]

The resilience of coral reefs in oligotrophic, (sub)tropical oceans is largely due to the symbiotic relationship between scleractinian corals and Symbiodiniaceae algae, which enables efficient internal nutrient recycling. Investigating the history of this coral symbiosis can provide insights into its role in sustaining the health of both present and future coral reefs. The isotopic composition of organic nitrogen (15N/14N or δ15N) bound within coral skeletons has been utilized to trace the existence of symbiosis in fossil corals, suggesting that coral symbiosis dates back to at least 210 million years ago. The basis of this proxy is that symbiotic corals are expected to exhibit lower δ15N compared to their non-symbiotic (aposymbiotic) counterparts within the same environments, owing to internal nitrogen recycling between the coral host and algal symbiont, and reduced leakage of low-δ15N ammonium into seawater. However, this hypothesis has not been adequately tested in contemporary settings. In a laboratory experiment, we examined the δ15N differences between the symbiotic and aposymbiotic branches within the same genetic backgrounds of the facultatively symbiotic coral Oculina arbuscula under well-fed conditions. Across five different genotypes in two separate experiments, symbiotic branches consistently showed lower δ15N than their aposymbiotic counterparts. These findings corroborate the use of δ15N as a proxy for identifying coral symbiosis in the past, particularly when multiple species of corals coexisted in the same environments. [ABSTRACT FROM AUTHOR]

Waste management is paramount to town planning and ancient civilizations across the world have spent resources and mobilized labor for waste disposal and reuse. The study of waste management practices offers a unique window into the daily lives, social organization, and environmental interactions of ancient societies. In the Indus Valley Civilization, known for its urban planning, understanding waste disposal in rural settlements provides crucial insights into the broader socio-economic landscape. While extensive research has documented sophisticated waste management systems in urban Indus centers, little is known about practices in rural settlements. This gap limits our understanding of regional variations and rural-urban dynamics within the civilization. In this paper, using isotopic and microscopic proxies, we characterize the waste disposed of at the rural Indus settlement of Kotada Bhadli to reconstruct the sources of waste, including heated animal dung, and burned vegetation. We propose that rural agro-pastoral settlements in Gujarat during the Indus Era systematically discarded such waste in specific locations. By characterizing waste produced at Kotada Bhadli, we are also able to reconstruct the natural environment and how the natural and cultural landscape around the settlement was exploited by the residents of the settlement for their domestic and occupational needs. Our identification of the attention paid to waste disposal by the inhabitants of Kotada Bhadli adds significant data to our understanding of waste disposal as an insight into past lives. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We studied the dynamics of stable carbon (δ13C) and nitrogen (δ15N) isotopes in litter from Norway spruce (NSL) (Picea abies) and Scots pine (SPL) (Pinus silvestris) during in situ decomposition over a period of more than 4 years. Relative to initial values, δ13CNSL showed a weak enrichment (0.33‰), whereas δ13CSPL was depleted (−0.74‰) at the end of decomposition. Both litter types experienced a depletion in δ15N during decomposition; δ15NNSL decreased by −1.74‰ and δ15NSPL decreased by −1.99‰. The effect of the selective preservation of acid-unhydrolyzable residue (AUR) in lowering δ13C of the residual litter was evident only in SPL. In the NSL, only in the initial stage did C/N have a large effect on the δ13C values. In the later stages, there was a non-linear decrease in δ13CNSL with a simultaneous increase in AUR concentrations, but the effect size was large, suggesting the role of lignin in driving δ13C of residues in later stages. Depletion in 15N in the residual litters concomitant with the increase in N concentration suggests bacterial transformation of the litter over fungal components. A consistent decline in δ15N values further implies that bacterial dominance prompted this by immobilizing nitrate depleted in 15N in the residual litter. [ABSTRACT FROM AUTHOR]

Ammonium is a key dissolved inorganic nitrogen (DIN) in the biogeochemical cycle of nitrogen in the ocean. Depending on the environment，the 15N natural abundance (δ15Nair ) of NH4+ can provide insights into N sources and mechanisms of N transformations in terrestrial ecosystems. A variety of methods have been developed for δ15Nair determination for NH4+ during the past several decades, such as the steam distillation method，ammonia diffusion method，ion exchange method and chemical conversion method. The former three methods are not unsuitable for low NH4+ concentration in seawater samples. In this study，a pretreatment method was developed for determination of nitrogen isotopic composition in ammonium based on the chemical method by hypobromite oxidation combined with sodium azide. To determine the reagent blank source and the effection on the yield rate and the value of δ15Nair, the appropriate reagent additions, NH4+ concentration were analyzed. There is no interference from any of the nitrogen-containing compounds tested. Higher concentration samples are readily diluted to lower concentration or taken a small volume. When the NH4+ concentration ranged from 5 to 50 μmol/L，the yield rate of ammonium converting to N2O was greater than 92%. And the calibration curves of ammonium isotopic standards with different abundances showed a good linearity The slope was 0.465 which was close to the theoretical values of 0.5. The standard deviation of δ15Nair measurements was 0.35‰ (n=5)，and the difference between the measured value and the reference value was 0.26‰. This method was used to determination of the nitrogen isotopic composition of dissolved ammonium in seawater, and δ15Nair (NH4+) value were between 11.46‰ to 22.31‰ . The standard deviation were between 0.20‰ to 0.62‰ (n=5). This method meet the requirements of ammonium nitrogen isotope analysis in seawater.

Associations between bryophytes and dinitrogen (N2)-fixing bacteria are a significant source of exogenous N in unmanaged boreal and possibly temperate ecosystems. However, the extent to which biological N2-fixation (BNF) applies to the boreal–temperate ecotone remains elusive. The current focus on common species limits our understanding of BNF at the community level. Our objective was to characterize the presence of cyanobacteria and BNF activity associated with bryophytes in the coastal forests of Fundy National Park (New Brunswick, Canada). In 2021, we harvested three liverwort and 11 moss species from two sites (71 samples) and measured environmental covariates (e.g., canopy composition and soil pH). We used stable isotope incubations with 15N2 gas in growth chambers to quantify potential BNF activity and used phycocyanin extractions as a cyanobacteria abundance proxy. Many species presented detectable BNF rates, which were similar to or higher than those of well-studied feather mosses. These included species that have rarely been found to contribute to BNF. While cyanobacteria were present on most samples, we found no positive association between abundance and BNF. Our findings are among the first records for bryophyte-associated BNF in the boreal–temperate ecotone of eastern Canada and offer insights into the potential role of this process in N cycling in coastal conifer-dominated forests. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Isotopes is the property of Journal of Isotopes Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The stable nitrogen isotopic composition (δ15N) has been widely used to quantify sources of ammonium (NH4+) in PM2.5. However, the overlap and uncertainty in δ15N values from different NH3 sources, coupled with their seasonal variability, hinder accurate identification of NH4+ source. Here, the δ15N values of various NH3 source samples collected by the active sampler were determined. Subsequently, we measured the δ15N values of NH4+ in PM2.5, which were collected seasonally in Tianjin. We found that the combustion‐related NH3 (c‐NH3) exhibiting higher δ15N values compared to volatile NH3 (v‐NH3), but all δ15N values was fell within the range reported by previous studies. Furthermore, inconsistent seasonal variations were observed in the δ15N‐NH3 values originating from emissions of agricultural soil and human excreta. The application of the Bayesian isotope mixing model (MixSIAR model) revealed a significant increase in the contribution of v‐NH3 to NH4+ when incorporating current source data, as opposed to previous data, for δ15N of NH3 source. Notably, the contribution of v‐NH3 (53.1%) to NH4+ was almost equivalent to that of c‐NH3 (46.9%) when considering the seasonal δ15N signatures of NH3 source. Additionally, the estimated contribution of v‐NH3 to NH4+ exhibited significant seasonal variability, which is more reasonable than in the non‐seasonal scenario. This study demonstrated that v‐NH3 and c‐NH3 contributed to NH4+ in PM2.5 in Tianjin almost equally, and it is highlighted that the seasonal δ15N values of NH3 sources should be considered when estimating the contributions of different NH3 sources to NH4+ in PM2.5 by the MixSIAR model. Plain Language Summary: Quantifying the source of NH4+ in PM2.5 through δ15N remains disputed, one possible reason was the uncertainty in δ15N values of NH3 sources. This study investigated the δ15N values from different NH3 sources collected by the active sampler, of which the δ15N‐NH3 from agricultural soils and human excreta emissions were characterized by season. Furthermore, we measured the δ15N values of NH4+ in PM2.5 collected seasonally in Tianjin to estimate the source contribution of NH4+ based on the MixSIAR model. Results found that a reasonable source‐resolved structure of NH4+ and their seasonal variations was obtained by the MixSIAR model using the seasonal δ15N data of NH3 source in this study. Specially, the contribution of c‐NH3 was significant overestimated when used the δ15N data of NH3 source from previous studies. Moreover, the estimated contribution of v‐NH3 to NH4+ exhibited significant seasonal variability, which is more reasonable than in the non‐seasonal scenario. These findings showed that the seasonal δ15N values of NH3 sources should be considered when estimating the contributions of different NH3 sources to NH4+ in PM2.5 using the MixSIAR model. Key Points: The δ15N values of six typical NH3 sources was systematically established using the active sampling methodThe δ15N‐NH3 values originating from agricultural soil and human excreta exhibit inconsistent seasonal variationsConsidering the seasonal δ15N variation in NH3 sources may obtained a reasonable seasonal source‐resolved structure of NH4+ [ABSTRACT FROM AUTHOR]

Global soil nitrogen (N) cycling remains poorly understood due to its complex driving mechanisms. Here, we present a comprehensive analysis of global soil δ15N, a stable isotopic signature indicative of the N input–output balance, using a machine‐learning approach on 10,676 observations from 2670 sites. Our findings reveal prevalent joint effects of climatic conditions, plant N‐use strategies, soil properties, and other natural and anthropogenic forcings on global soil δ15N. The joint effects of multiple drivers govern the latitudinal distribution of soil δ15N, with more rapid N cycling at lower latitudes than at higher latitudes. In contrast to previous climate‐focused models, our data‐driven model more accurately simulates spatial changes in global soil δ15N, highlighting the need to consider the joint effects of multiple drivers to estimate the Earth's N budget. These insights contribute to the reconciliation of discordances among empirical, theoretical, and modeling studies on soil N cycling, as well as sustainable N management. [ABSTRACT FROM AUTHOR]

Quantifying the tropic position (TP) of an animal species is key to understanding its ecosystem function. While both bulk and compound-specific analyses of stable isotopes are widely used for this purpose, few studies have assessed the consistency between and within such approaches. Champsocephalus gunnari is a specialist teleost that predates almost exclusively on Antarctic krill Euphausia superba. This well-known and nearly constant trophic relationship makes C. gunnari particularly suitable for assessing consistency between TP methods under field conditions. In the present work, we produced and compared TP estimates for C. gunnari and its main prey using a standard bulk and two amino acid-specific stable isotope approaches (CSI-AA). One based on the difference between glutamate and phenylalanine (TPGlx-Phe), and the other on the proline-phenylalanine difference (TPPro-Phe). To do that, samples from C. gunnari, E. superba and four other pelagic invertebrate and fish species, all potential prey for C.gunnari, were collected off the South Orkney Islands between January and March 2019, analyzed using standard isotopic ratio mass spectrometry methods and interpreted following a Bayesian approach. Median estimates (CI95%) for C. gunnari were similar between TPbulk (3.6; CI95%: 3.0-4.8) and TPGlx-Phe(3.4; CI95%:3.2-3.6), and lower for TPPro-Phe (3.1; CI95%:3.0-3.3). TP differences between C. gunnari and E. superba were 1.4, 1.1 and 1.2, all compatible with expectations from the monospecific diet of this predator (ΔTP=1). While these results suggest greater accuracy for Glx-Phe and Pro-Phe, differences observed between both CSI-AA approaches suggests these methods may require further validation before becoming a standard tool for trophic ecology. [ABSTRACT FROM AUTHOR]

The resilience of coral reefs in oligotrophic, (sub)tropical oceans is largely due to the symbiotic relationship between scleractinian corals and Symbiodiniaceae algae, which enables efficient internal nutrient recycling. Investigating the history of this coral symbiosis can provide insights into its role in sustaining the health of both present and future coral reefs. The isotopic composition of organic nitrogen (15N/14N or δ15N) bound within coral skeletons has been utilized to trace the existence of symbiosis in fossil corals, suggesting that coral symbiosis dates back to at least 210 million years ago. The basis of this proxy is that symbiotic corals are expected to exhibit lower δ15N compared to their non-symbiotic (aposymbiotic) counterparts within the same environments, owing to internal nitrogen recycling between the coral host and algal symbiont, and reduced leakage of low-δ15N ammonium into seawater. However, this hypothesis has not been adequately tested in contemporary settings. In a laboratory experiment, we examined the δ15N differences between the symbiotic and aposymbiotic branches within the same genetic backgrounds of the facultatively symbiotic coral Oculina arbuscula under well-fed conditions. Across five different genotypes in two separate experiments, symbiotic branches consistently showed lower δ15N than their aposymbiotic counterparts. These findings corroborate the use of δ15N as a proxy for identifying coral symbiosis in the past, particularly when multiple species of corals coexisted in the same environments.

[Display omitted] Aerosol ammonium (NH 4 +), mainly produced from the reactions of ammonia (NH 3) with acids in the atmosphere, has significant impacts on air pollution, radiative forcing, and human health. Understanding the source and formation mechanism of NH 4 + can provide scientific insights into air quality improvements. However, the sources of NH 3 in urban areas are not well understood, and few studies focus on NH 3 /NH 4 + at different heights within the atmospheric boundary layer, which hinders a comprehensive understanding of aerosol NH 4 +. In this study, we perform both field observation and modeling studies (the Community Multiscale Air Quality, CMAQ) to investigate regional NH 3 emission sources and vertically resolved NH 4 + formation mechanisms during the winter in Beijing. Both stable nitrogen isotope analyses and CMAQ model suggest that combustion-related NH 3 emissions, including fossil fuel sources, NH 3 slip, and biomass burning, are important sources of aerosol NH 4 + with more than 60% contribution occurring on heavily polluted days. In contrast, volatilization-related NH 3 sources (livestock breeding, N-fertilizer application, and human waste) are dominant on clean days. Combustion-related NH 3 is mostly local from Beijing, and biomass burning is likely an important NH 3 source (∼15%–20%) that was previously overlooked. More effective control strategies such as the two-product (e.g., reducing both SO 2 and NH 3) control policy should be considered to improve air quality. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In recent years, the total nitrogen concentration in Taihu Lake has decreased significantly. Denitrification, as the main nitrogen removal process, is the key reason for the decrease. Here, the denitrification parameter values in the Environmental Fluid Dynamic Code (EFDC) model were calculated based on isotope-labeled denitrification experiment instead of selecting the recommended values directly. This study further focused on EFDC denitrification parameter derivation with an experimental denitrification rate (Dtot) to reduce simulation errors. According to the EFDC nitrate deposition flux mechanism, the conversion equation between the denitrification rate of the first sediment layer ( κ 1 , N O 3 ) in EFDC and Dtot was successfully derived. The results revealed a linear correlation between κ 1 , N O 3 and (Dtot)1/2. The κ 1 , N O 3 values of sampling points ranged from 0.25 to 0.27 m·day−1, within the range of model parameters. After substituting κ 1 , N O 3 into the Taihu Lake EFDC model, the average percentage bias and determination coefficient of total nitrogen were 16.25% and 0.87, respectively. The average total nitrogen concentration reduction caused by denitrification at water quality calibration points ranged from 0.027 to 0.305 mg·L−1. [ABSTRACT FROM AUTHOR]

Tambaqui production is commonly performed in fertilized ponds, considering that this species feeds from zooplankton throughout its life. This study evaluated plankton's participation in the production of tambaqui juveniles in ponds using different stocking densities. A total of 72,000 fish (1.9 ± 0.01 cm and 0.4 ± 0.1 g) were stocked in 12 ponds (600 m2), in the densities of 5, 10, or 15 fish.m−2, with four replicates in a completely randomized design. Fish were fed twice a day to the point of satiety, with a commercial diet containing 36% of crude protein for 56 days. Zootechnical performance parameters were evaluated, and limnological variables were monitored. With the aid of stable isotopes, both the diet and plankton participation were assessed in the produced biomass of fish. Turbidity and Secchi were the only limnological variables that varied due to stocking density, while final biomass and final average density were the only zootechnical indexes that presented differences. Plankton contributed to the formation of muscles throughout the production period, with an average participation of 22.75 ± 12.82%. [ABSTRACT FROM AUTHOR]

Quantifying the tropic position (TP) of an animal species is key to understanding its ecosystem function. While both bulk and compound-specific analyses of stable isotopes are widely used for this purpose, few studies have assessed the consistency between and within such approaches. Champsocephalus gunnari is a specialist teleost that predates almost exclusively on Antarctic krill Euphausia superba. This well-known and nearly constant trophic relationship makes C. gunnari particularly suitable for assessing consistency between TP methods under field conditions. In the present work, we produced and compared TP estimates for C. gunnari and its main prey using a standard bulk and two amino acid-specific stable isotope approaches (CSI-AA). One based on the difference between glutamate and phenylalanine (TPGlx-Phe), and the other on the proline-phenylalanine difference (TPPro-Phe). To do that, samples from C. gunnari, E. superba and four other pelagic invertebrate and fish species, all potential prey for C.gunnari, were collected off the South Orkney Islands between January and March 2019, analyzed using standard isotopic ratio mass spectrometry methods and interpreted following a Bayesian approach. Median estimates (CI95%) for C. gunnari were similar between TPbulk (3.6; CI95%: 3.0-4.8) and TPGlx-Phe(3.4; CI95%:3.2-3.6), and lower for TPPro-Phe (3.1; CI95%:3.0-3.3). TP differences between C. gunnari and E. superba were 1.4, 1.1 and 1.2, all compatible with expectations from the monospecific diet of this predator (ΔTP=1). While these results suggest greater accuracy for Glx-Phe and Pro-Phe, differences observed between both CSI-AA approaches suggests these methods may require further validation before becoming a standard tool for trophic ecology.

Tree-ring δ15N may depict site-specific, long-term patterns in nitrogen (N) dynamics under N2-fixing species, but field trials with N2-fixing tree species are lacking and the relationship of temporal patterns in tree-ring δ15N to soil N dynamics is controversial. We examined whether the tree-ring δ15N of N2-fixing red alder (Alnus rubra Bong.) would mirror N accretion rates and δ15N of soils and whether the influence of alder-fixed N could be observed in the wood of a neighboring conifer. We sampled a 27-year-old replacement series trial on south-eastern Vancouver Island, with red alder and coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) planted in five proportions (0/100, 11/89, 25/75, 50/50 and 100/0) at a uniform stem density. An escalation in forest floor N content was evident with an increasing proportion of red alder, equivalent to a difference of ~750 kg N ha−1 between 100% Douglas-fir versus 100% alder. The forest floor horizon also had high δ15N values in treatments with more red alder. Red alder had a consistent quadratic fit in tree-ring δ15N over time, with a net increase of |$\sim$| 1.5‰, on average, from initial values, followed by a plateau or slight decline. Douglas-fir tree-ring δ15N, in contrast, was largely unchanged over time (in three of four plots) but was significantly higher in the 50/50 mix. The minor differences in current leaf litter N content and δ15N between alder and Douglas-fir, coupled with declining growth in red alder, suggests the plateau or declining trend in alder tree-ring δ15N could coincide with lower N2-fixation rates, potentially by loss in alder vigor at canopy closure, or down-regulation via nitrate availability. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition is a key process influencing plant‐soil N processes and associated functions of forest ecosystems. However, the N deposition into soils based on open‐field precipitation observations remains inaccurate due to the unconstrained precipitation‐canopy N exchanges, which prevents a better evaluation of N deposition effects on forest N cycles and functions. Nitrate (NO3− ${{\text{NO}}_{3}}^{-}$) is a major form of reactive N. Based on a data synthesis of fluxes and isotopes (15N, 17O, 18O) of atmospheric NO3− ${{\text{NO}}_{3}}^{-}$ inputs in forests, here we constructed a new method to quantify fractions and fluxes of throughfall NO3− ${{\text{NO}}_{3}}^{-}$ (t‐NO3− $\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$) contributors (nitrification (n‐NO3− $\mathrm{n}\mbox{-}{{\text{NO}}_{3}}^{-}$) and particulates (p‐NO3− $\mathrm{p}\mbox{-}{{\text{NO}}_{3}}^{-}$) in canopies, the original precipitation (b‐NO3− $\mathrm{b}\mbox{-}{{\text{NO}}_{3}}^{-}$)) and then constrain precipitation‐canopy NO3− ${{\text{NO}}_{3}}^{-}$ exchanges (i.e., t‐NO3− $\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$ gains from canopy and b‐NO3− $\mathrm{b}\mbox{-}{{\text{NO}}_{3}}^{-}$ losses due to canopy retention). Generally, t‐NO3− $\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$ was higher in fluxes but lower in N and O isotopes than b‐NO3− $\mathrm{b}\mbox{-}{{\text{NO}}_{3}}^{-}$, suggesting higher gains than losses and canopy nitrification as a gain contributor. 10%−18% and 40%−47% of t‐NO3− $\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$ were gained from canopy n‐NO3− $\mathrm{n}\mbox{-}{{\text{NO}}_{3}}^{-}$ and p‐NO3− $\mathrm{p}\mbox{-}{{\text{NO}}_{3}}^{-}$, respectively, while 43% ± 25% and 20% ± 74% of the original b‐NO3− $\mathrm{b}\mbox{-}{{\text{NO}}_{3}}^{-}$ were lost after passing through canopies of broadleaved and coniferous forests, respectively. Importantly, both t‐NO3− $\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$ gain and b‐NO3− $\mathrm{b}\mbox{-}{{\text{NO}}_{3}}^{-}$ loss fluxes were found increasing with the b‐NO3− $\mathrm{b}\mbox{-}{{\text{NO}}_{3}}^{-}$ fluxes. This work unlocked fractions and fluxes of major precipitation‐canopy NO3− ${{\text{NO}}_{3}}^{-}$ exchange processes and revealed a stimulating mechanism of atmospheric NO3− ${{\text{NO}}_{3}}^{-}$ pollution on precipitation‐canopy NO3− ${{\text{NO}}_{3}}^{-}$ exchanges. Plain Language Summary: Canopy is an important interface of forest‐atmosphere substance exchanges. It is also a biological barrier for the inputs of atmospheric pollutants into soils. Based on a comprehensive data synthesis and method innovation, we found generally higher throughfall nitrate gains from canopy nitrification and particulates than the retention losses of nitrate from the original precipitation, which caused the generally higher nitrate fluxes in throughfall under canopies than in bulk precipitation of open fields. These results demonstrate that atmospheric nitrate inputs into forest soils had been underrated when dry deposition was not included and only precipitation data of open fields were used for evaluating soil or forest nitrogen input‐output dynamics and their ecological effects. Besides, the degree of atmospheric nitrate loading and forest type were recognized as key abiotic and biotic factors influencing precipitation‐canopy nitrate exchanges, respectively. This finding underscores that anthropogenic nitrogen pollution and forest functional traits play critical roles in regulating canopy nitrate biogeochemistry and then source contributions and fluxes of atmospheric inputs into soils. New insights in this work should be considered in evaluating the forest nitrogen cycle and its effects on the carbon cycle and biodiversity for a sustainable forest management. Key Points: Throughfall nitrate (t‐NO3− $\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$) showed generally higher fluxes but lower isotopes than precipitation nitrate in open fields (b‐NO3− $\mathrm{b}\mbox{-}{{\text{NO}}_{3}}^{-}$)Canopy nitrification and particulates contributed 10%−18% and 40%−47% of t‐NO3− $\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$, meanwhile canopy retained 28% ± 62% of the original b‐NO3− $\mathrm{b}\mbox{-}{{\text{NO}}_{3}}^{-}$Precipitation‐canopy NO3− ${{\text{NO}}_{3}}^{-}$ exchanges increased with the site‐based level of atmospheric NO3− ${\text{NO}}_{3}^{-}$ loading [ABSTRACT FROM AUTHOR]

To bridge the gap between lab-scale microcosm research and field application in the compound-specific stable isotope analysis (CSIA) of atrazine, we studied the characteristics of carbon and nitrogen isotope fractionation in the atrazine degradation processes within a constructed wetland. In the wetland, we observed multiple element (C, N) isotope fractionation parameters, such as kinetic isotope effects and dual isotope slopes. These parameters are very consistent with those observed in the cultivation of AtzA- or TrzN-harboring strains, suggesting a similarity in the pathway and reaction mechanism of atrazine biodegradation between the two settings. However, we recorded variable carbon ( ε C :   −3.2 ± 0.6‰ to −4.3 ± 0.6‰) and nitrogen isotope fractionation ( ε N :   1.0 ± 0.3‰ to 2.2 ± 0.3‰) across different phases. This variance could lead to an over- or underestimation of the biodegradation extent of atrazine when employing the large or small enrichment factor of the carbon isotope. Intriguingly, the estimation accuracy improved considerably when using the enrichment factor (−4.6‰) derived from the batch cultivation of the pore water. This study advances the application of CSIA in tracking atrazine biodegradation processes in ecosystems, and it also underlines the importance of the careful selection and application of the enrichment factor in quantifying the intrinsic biodegradation of atrazine in ecosystems. [ABSTRACT FROM AUTHOR]

Spatial information of the natural abundance of soil nitrogen stable isotope (δ15N) is beneficial for deeply understanding the terrestrial nitrogen (N) cycle. However, to date, the precise global map of soil δ15N still lacks. In this study, based on the measured soil δ15N data by Craine et al. (2015) (https://doi.org/10.1038/srep08280) and related environmental variables including soil, topography, vegetation, and climate, we constructed the optimal relationship model between soil δ15N and environmental variables, and mapped the global pattern of soil δ15N at 0.1° × 0.1° resolution (in natural terrestrial ecosystem). Results indicated that satisfied performance was achieved (R2 = 0.68 and RMSE = 1.26‰) by separately building the optimal relationship models for soil δ15N in each of five climate zones (Tropical, Arid, Temperate, Cold and Polar) using the random forest regression algorithm. In addition, critical controls of the soil δ15N in different climate zones were thus identified based on the variable importance calculated by each random forest regression model. In the Tropical zone, soil δ15N might be primarily regulated by microbial N loss, and soil pH and organic matter were identified as two most important factors. In the Arid zone, abiotically gaseous N loss regulated by solar radiation would be the critical controls of soil δ15N. In the Temperate zone, temperature-related variables were identified as the critical controlling factors, and in the Cold zone, soil water and heat conditions had the equally greater importance, and bulk density was the dominated factor in the Polar zone. Furthermore, the predicted global soil δ15N ranged from −0.44‰ to 12.59‰, with the mean value of 5.06‰, and the standard deviation of 1.74‰. Significantly higher soil δ15N (P

Aims: 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. Methods: 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. Results: 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. Conclusions: 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. [ABSTRACT FROM AUTHOR]

Avian populations can substantially influence lacustrine nutrient loading and biogeochemical cycling through guano deposition. Here, we examine the influence of climate-forced avian migration throughout the Holocene on Kettle Lake, North Dakota, using stable nitrogen and carbon isotope values (δ15N, δ13C) of lake sediment organic matter. Carbon content and δ13C values are negatively correlated with δ15N and appear to be driven by changes in charcoal abundance and watershed vegetation, respectively. We find enriched δ15N values when the guano mineral struvite is present in the lake sediment core in the early to Mid-Holocene. A strong δ15N-percent Nitrogen content relationship during periods with struvite, relative to periods without struvite, indicates that guano deposition from mass bird visitations altered past nitrogen cycle processes, likely through enhanced denitrification. These results attest to the ability of waterfowl to alter lacustrine N-cycling in a mid-continental North American lake, and indicate that paleo-N data in this particular lake are recording a unique history that does not necessarily represent regional paleoenvironmental conditions. However, a significant, positive relationship between δ15N and Ambrosia and Amaranthaceae pollen abundance suggests avian visitation and its impacts on the N-cycle occurred during periods of anomalously wet summers superimposed on the background conditions of early to Mid-Holocene drought. [ABSTRACT FROM AUTHOR]

In this study, nitrate in standard samples, seawater and lake water and tap water samples were converted to N2O using bacterial denitrification and chemical conversion, the nitrogen and oxygen isotope composition were determined by Isotope Ratio Mass Spectrometry (IRMS), and the parameters of the nitrogen and oxygen isootope calibration curve, the precision, accuracy and detection limit of the two conversion methods were obtained. The results show that: (1) The yield rates of nitrate converting to N2O were all greater than 90%. (2) The slope of the nitrogen isotope calibration curve for the bacterial denitrification and the chemical conversion were 0.959 and 0.481, respectively, Close to the respective theoretical values of 1 and 0.5; The slope of the oxygen isotope calibration curve were 0.908 and 0.697, respectively, there is a certain deviation from the theoretical value of 1. (3) The standard deviations of nitrogen isotopes determined by the two methods were less than 0.5‰, The standard deviations of oxygen isotopes were all less than 1‰. (4) The detection limit of nitrate nitrogen and oxygen isotope test by bacterial denitrification and chemical conversion is 4.4 nmol and 7.54 nmol, respectively. (5) Both methods can more accurately determine the nitrogen isotopic composition of nitrate in the three types of samples (sea water, lake water and tap water). The results were consistent by the two methods. The difference of nitrogen isotope results by the two methods were between 0.11‰ and 0.77‰. The oxygen isotope difference were from 3.67‰ to 5.75‰, It was shown that oxygen isotopic fractionation were occur when the nitrate were reduced to N2O, and the degree of oxygen isotopic fractionation were difference in the two conversion methods.

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The emergence of 100‐Kyr glacial cycles (The Mid‐Pleistocene Transition [MPT]) is attributed in part to slower global overturning circulation and iron stimulation of biological carbon drawdown in the Southern Ocean. We present foraminifera‐bound nitrogen isotope values and polar planktic foraminifera abundances from the Agulhas Plateau that show that increases in biogenic sediment accumulation coincide with northward migrations of the Subtropical Frontal Zone (STFZ) and elevated foraminifera‐bound nitrogen isotope values during MPT glacial episodes. The nitrogen isotope values of two planktic foraminifera species, Globigerina bulloides and Globorotalia inflata show remarkable coherence amongst the sea surface temperature gradient between the STFZ and SAZ, and polar foraminifera abundances, indicating a strong relationship between nitrogen isotope dynamics above the Agulhas Plateau and migrations of the STFZ. Northward migration of the STFZ may have been essential to prolonging glacial intervals by increasing deep ocean carbon storage via a northward shift of the South Westerly Winds and a reduction in upwelling, delivery of fresher surface waters into the upper limb of global overturning circulation, or inhibiting heat and salt delivery to the Atlantic as Agulhas Leakage. Plain Language Summary: The Mid‐Pleistocene Transition (MPT) is a unique period of time, during which the natural rhythm of Earth's climate shifted, the pace of glacial and interglacial cycles changed from 40,000 years to 100,000 years as ice sheets expanded, carbon accumulated in the deep ocean, and the planet cooled. The exact cause of these changes is unclear, but internal system feedbacks were likely at play. As climate changes today and the oceans increasingly take up carbon, the MPT provides a unique case study to investigate Earth's natural climate system and important carbon cycle feedbacks. In this paper we use the nitrogen isotopic composition of plankton shells and other biogeochemical records to show that leading up to the MPT the Southern Ocean underwent major physical changes and expanded as 100,000 years glacial cycles emerged. Our data indicates that the expansion of the Southern Ocean delivered cold, nutrient rich waters northward where they could mix with warm, salty Indian and Atlantic Ocean waters as hypothesized by other studies. Key Points: Foraminifera‐bound nitrogen isotope values from the Agulhas Plateau record latitudinal migrations of the Subtropical FrontElevated foraminifera‐bound nitrogen isotope values after 900 ka are consistent with Southern sourced nitrateSouthern Ocean contraction during a "super interglacial" brings more subtropical nitrate to the Agulhas Plateau [ABSTRACT FROM AUTHOR]

Eclogitic diamond formation can be associated with interactions between subducted slabs and ambient mantle. To gain a better understanding of the extent of chemical exchange between slabs and ambient mantle and the mechanisms of coeval diamond formation, we examined 16 diamonds with eclogitic garnet inclusions from the Koidu kimberlite complex in Sierra Leone (West African Craton). We analyzed the 16 garnet inclusions for major element, trace element and oxygen isotope (δ18O) compositions and their host diamonds for carbon (δ13C) and nitrogen (δ15N) isotope compositions. The garnet inclusions have δ18O values ranging from +5.4 to +12.1‰ (median = +11.3‰) and all but two have δ18O values ≥+9.9‰. Such high δ18O values indicate a link to protoliths that had undergone extensive low-temperature alteration by seawater, which occurs in the uppermost basaltic layer of oceanic crust, prior to subduction. Diamonds hosting the high δ18O garnets have a crustal δ13C signature (−29.6 to −19.4‰) paired with δ15N values (−5.6 to +1.3‰, with one outlier at +9.9‰) implying typically only minor 15N enrichment. This apparent decoupling of δ18O and δ13C from δ15N indicates diamond formation in an eclogitic substrate where garnet oxygen isotope compositions are inherited from altered low-pressure protoliths, diamond carbon is principally derived from biogenic carbonate and organic matter, and diamond nitrogen is variably added by an external, mantle-derived fluid that prompted diamond formation. Of the two remaining garnet inclusions, one has mantle-like δ18O (+5.4‰) and a positive Eu anomaly, suggesting derivation from gabbroic protoliths originally located deep in the oceanic crust where significant alteration by seawater did not occur. Based on mantle-like δ13C (−4.7‰) and δ15N (−6.9‰), the associated diamond formed from mantle-derived fluids/melts. Relative to the other Koidu garnet inclusions, the final garnet has a small majorite component (formation pressure ∼8 GPa), high Mg# (79.0), elevated Cr# (0.90), and low δ18O (+6.3‰), suggesting encapsulation during infiltration of slab-derived melts into surrounding asthenospheric peridotite, associated with a high degree of chemical exchange between slab- and mantle-derived components. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Isotopes is the property of Journal of Isotopes Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, the nitrogen and oxygen isotope compositions of nitrite in the upper 150 m water column of the Amundsen Sea in the summer of 2019 and 2020 were measured to reveal the distribution and transformation of nitrite in the euphotic zone of the Southern Ocean. We found that primary nitrite maxima (PNMs) are widely present in the Amundsen Sea, where the depth of occurrence deepens from east to west and nitrite concentrations increases. Evidence from dual isotopes suggests that the formation of PNMs in all regions of the Amundsen Sea is dominated by ammonia oxidation. More importantly, the nitrogen and oxygen isotope compositions of nitrite in the Amundsen Sea mixed layer are abnormal, and their depth profiles are mirror symmetrical. Isotopic anomalies exhibit spatial variations, with central surface water having the lowest nitrogen isotope composition (−89.9‰±0.2‰) and western surface water having the highest oxygen isotope composition (63.3‰±0.3‰). Isotopic exchange reaction between nitrate and nitrite is responsible for these isotope anomalies, as both nitrogen and oxygen isotopes have large isotopic fractionation and opposite enrichment effects. This proves that isotopic exchange reaction operates extensively in different regions of the Amundsen Sea. Our study highlights the unique role of dual isotopes of nitrite in deepening the understanding of nitrogen cycle. Further studies on ammonia oxidation and isotopic exchange between nitrate and nitrite are warranted in the future to understand their roles in the nitrogen cycle in the Southern Ocean. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Inorganic Analytical Chemistry / Zhongguo Wuji Fenxi Huaxue is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In dark gray forest soil, the use of 15N fertilizer nitrogen by spring wheat when seeds were inoculated with microbial biopreparations was assessed. The use of the method under study increased the weight of grain on the PK background by 25–42%. Increases from inoculation with preparations based on diazotrophs Ch-13 and V 167 strains were equivalent and amounted to 78–97 g/m2. In the variant with V 417, the increase reached 132 g/m2 and was at the level of use of N45 (143 g/m2). In combination with N45, the biopreparation based on strain Ch-13 was characterized by maximum efficiency. When using biopreparations on the PK-background, the accumulation of N in the yield increased by 2.33–2.64 g/m2 and by 1.33–1.70 g/m2 on the NRK background. In the variants with biopreparations, the 20% of the yield was formed due to biological nitrogen, while its greatest accumulation (24.8%) occurred when using V 417. The maximum share of 15N (23.7%) in the yield was noted when N90 was applied. When using biopreparations, plants accumulate approximately 8.5% of "extra"-N and its highest content (11.5–12.1%) was recorded when Naa was added. Mineral fertilizer nitrogen mainly accumulates in grain (95–96%) and only 4–5% accumulate in spring wheat straw. When applying N45 and N90, plants use 46 and 42% of fertilizer nitrogen, respectively, and the use of biopreparations increases the value of this indicator to 51–53%. Approximately 33–36% of the introduced dose of 15N is fixed in the soil, and this indicator increased up to 30% when using biopreparations. Losses of 15N reach 33–36%, while losses decrease to 17–19% with the introduction of biopreparations. The minimum accumulation of fertilizer nitrogen in plants (42%), the maximum fixation in the soil (36%), and losses (23%) were observed when N90 was applied. [ABSTRACT FROM AUTHOR]

Seasonings such as naturally fermented soy sauce without added monosodium glutamate (MSG), are currently a growth market in China. However, fraudulent and mislabeled zero-added MSG soy sauce may cause a risk of excessive MSG intake, increasing food safety issues for consumers. This study investigates stable carbon and nitrogen isotopes and 16 amino acids in typical Chinese in-market soy sauces and uses a similarity method to establish criteria to authenticate MSG addition claims. Results reveal most zero-added MSG soy sauces had lower δ 13C values (−25.2 ‰ to −17.7 ‰) and glutamic acid concentrations (8.97 mg mL−1 to 34.76 mg mL−1), and higher δ 15N values (−0.27 ‰ +0.95 ‰) and other amino acid concentrations than added-MSG labeled samples. A combined approach, using isotopes, amino acids, similarity coefficients and uncertainty values, was evaluated to rapidly and accurately identify zero-added MSG soy sauces from MSG containing counterparts. [Display omitted] • Isotopes and amino acids profiles were characterized for in-market soy sauces. • Strong correlations were found between isotopes and amino acids. • A new approach is proposed using similarity analysis to classify soy sauce. • A decision tree is established to identify zero-added MSG soy sauce. [ABSTRACT FROM AUTHOR]

The objectives of this research were to: i) develop a mechanistic understanding of the synergy between microbial co-inoculation, nitrogen (N) fertilizer, and maize plants on biological 15N fixation, and 15N-recovery from applied fertilizers; and ii) explore the mechanist effects of microbial co-inoculation on N fractionations and derivation (fertilizer, atmosphere and soil), physiological responses on water use and carboxylation efficiencies and growth by using two different isotopic techniques under field conditions. Treatments included four seed inoculations (Control, B. subtilis , A. brasilense , and the combination of B. subtilis and A. brasilense), along with five levels of N application (0–240 kg N ha−1). Overall, the results indicate that maize co-inoculation with the above-mentioned bacteria enhanced photosynthetic efficiency leading to improved carboxylation efficiency and instantaneous water use efficiency in maize plants, likely due to an increase in net photosynthetic rate. This effect was more evident under low N availability. The findings also suggest that co-inoculation enhanced the ability of maize plants to absorb CO 2 , adjust to different soil N levels, and carry out photosynthesis, which resulted in higher carbon fixation and better maize growth. The N obtained from the atmosphere resulting from inoculation ranged from 25 to 50 kg N ha−1. Nonetheless, N application rates exceeding 186 kg N ha−1 substantially diminished the ability of these bacteria to fix N 2. The combination of inoculation with the application of 120–180 kg N ha−1 led to a synergistic effect resulting in the greatest N-use efficiency, -recovery and grain yield. • Microbial co-inoculation work with a synergistic effect towards BNF and optimizing NUE. • BNF contribution of microbial co-inoculation can range from 35 to 50 kg N ha−1. • N rates can be reduced from 240 to 173 kg N ha−1 while increasing corn yield (5.8%). [ABSTRACT FROM AUTHOR]

The early Carboniferous experienced profound climate cooling that drove the Earth's climate from a mid-Paleozoic greenhouse into the Late Paleozoic Ice Age. Several climate cooling events have been reported, including the Tournaisian and Visean (early to mid-Early Carboniferous). In this study, we perform multi-proxy analyses (organic carbon isotopes, nitrogen isotopes, major and trace elements and organic petrology/geochemistry) of samples from an early Carboniferous section in Nandan region (Guangxi, China). Our goal is to investigate the global carbon‑nitrogen cycle, and associated oceanic productivity and redox perturbations, during a key climatic transition interval, as well as the controls on organic matter enrichment in the sediments. The carbon and nitrogen isotope profiles of the Nandan section record major perturbations during the mid-Tournaisian and early Visean. The mid-Tournaisian carbon isotope excursion (TICE) is marked by a positive δ13C org shift of 1.8 ‰ (from −27.7 ‰ to −25.9 ‰), correlating with a positive δ15N shift. The early Visean carbon isotope excursion (VICE) is characterized by a positive shift in δ13C org (from −28.2 to −25.5 ‰, with an excursion magnitude of 2.7 ‰), but associated with a negative shift in δ15N (from +5 ‰ to +4 ‰). The positive δ13C org excursions during these events most likely reflect enhanced organic matter burial with expansion of anoxic seafloor in the global ocean. The drop in nitrogen isotope values in the early Visean is interpreted to be linked with less denitrification under more oxic conditions. The decrease of organic matter contents up section is consistent with the shift to more oxic conditions and increased sedimentary dilution caused by sea-level fall, which is ultimately controlled by orogenic events and climate cooling. • The C and N cycle during the mid-Tournaisian and early Visean were studied. • The positive δ13C org excursions may reflect enhanced organic carbon burial. • The drop of δ15N in the early Visean may be linked with reduced denitrification. • Organic matter enrichment in the Luzhai Formation linked with climate cooling. [ABSTRACT FROM AUTHOR]

The majority of soil nitrogen is closely associated with soil organic matter, the cleavage of high molecular weight organic N such as protein to smaller soluble compounds (e.g amino acids) is a key step in the terrestrial N cycle. Therefore, as amino acids occupy a central position in understanding the N biogeochemical cycling processes and ecosystem functions, using natural abundance level isotopic information of amino acids or the heavier isotope 15N as a tracer helps advance the knowledge of soil fertility and its biological mechanism. Currently isotope pool dilution approach and compound-specific isotope analysis (CSIA) approaches have been successful established to measure amino acid in soils. However, both of them need large sample requirements and labor-consuming isolation procedures for the isotope analysis of amino acids. In this study, a novel distillation-chemical conversion N2O approach based on the 15N analysis by the oxidation of amino groups to NO2- and further reduction to N2O was described, followed by PreCon isotope ratio mass spectrometry (PreCon-IRMS). Sample preparation was carried out by our self-developed device-automatic micro-nitrogen conversion N2O generating device, allowing either helium (He) purging of gas or liquid charging from a range of suitable, airtight bottles. The reaction conditions for the N2O production were explored and optimized, including the hypobromite concentration, NaOH concentration, and amino acid mixtures concentration. The nitrogen stable isotope abundance in standard solutions of amino acid mixtures with different concentrations and 15N abundance, as well as the nitrogen stable isotope abundance of free amino acids in tested soil were analyzed by using the newly developed pretreatment method combined with the PreCon-IRMS system. The results showed that the developed method coupled IRMS analytical system was able to measure the 15N abundance in all standard solutions and soil extracts with good precision of 0.2%-08% (CV

Nitrate is a prominent pollutant in water bodies around the world. The isotopes in nitrate provide an effective approach to trace the sources and transformations of nitrate in water bodies. However, determination of isotopic composition by conventional analytical techniques is time-consuming, laborious, and expensive, and alternative methods are urgently needed. In this study, the rapid determination of 15NO3− in water bodies using Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) coupled with a deconvolution algorithm and a partial least squares regression (PLSR) model was explored. The results indicated that the characteristic peaks of 14NO3−/15NO3− mixtures with varied 14N/15N ratios were observed, and the proportion of 15NO3− was negatively correlated with the wavenumber of absorption peaks. The PLSR models for nitrate prediction of 14NO3−/15NO3− mixtures with different proportions were established based on deconvoluted spectra, which exhibited good performance with the ratio of prediction to deviation (RPD) values of more than 2.0 and the correlation coefficients (R2) of more than 0.84. Overall, the spectra pretreatment by the deconvolution algorithm dramatically improved the prediction models. Therefore, FTIR-ATR combined with deconvolution and PLSR provided a rapid, simple, and affordable method for determination of 15NO3− content in water bodies, which would facilitate and enhance the study of nitrate sources and water environment quality management. [ABSTRACT FROM AUTHOR]

The assessment of nitrogen cycle processes in paleomarine and paleolake systems commonly relies solely on total nitrogen isotopes. If organic nitrogen and adsorbed nitrate can be effectively extracted from samples, the application of nitrogen isotopic systematics in different N forms would be beneficial for reconstructing the nitrogen cycle process in pore water and would mutually complement water chemistry information. According to the variations in δ13Corg, δ15NTN, δ15Norg and δ15Nnitrate data of the Cretaceous Nenjiang Formation in the Songliao Basin, NE China, the profile could be divided into three intervals (intervals A–C). We attribute the anomalously high δ15Nnitrate (∼+20‰) from intervals A and C to the effect of sedimentary denitrification that occurred in the benthic sediments during the early diagenetic stage. We also recognize the intimate relationship between δ15Nnitrate and δ15Norg values, which are interpreted to reflect the effect of water column denitrification in the bottom waters and/or surface pore water. Based on the comparison of nitrogen isotope variability and the evolving environmental context, we interpret the water column denitrification as primarily reflecting anoxic bottom water or surface pore waters, while the sedimentary denitrification indicated by abnormally high δ15Nnitrate can effectively represent oxic bottom water. This study not only reveals that the adsorbed nitrate can be well extracted from mudstones with low thermal decomposition degrees but also suggests that the organic nitrogen‐nitrate isotope proxies can be used as a potential parameter to track the redox structure in water masses. Key Points: Abnormally high nitrate nitrogen isotopes imply massive sedimentary denitrificationSimilar organic nitrogen isotope and nitrate nitrogen isotope distributions suggest water denitrificationOrganic nitrogen isotope and nitrate nitrogen isotope proxies provide independent evidence for redox structure [ABSTRACT FROM AUTHOR]

Energy sources and trophic interactions among vent fauna were investigated in deep-sea hydrothermal vents in the North Fiji Basin (NFB), Southwest Pacific, using stable sulfur, carbon, and nitrogen isotopes. A Bayesian isotope mixing model (MixSIAR) was used to quantify the proportions of energy sources for symbiont-bearing taxa. Based on these results, symbionts of host taxa such as the hairy snail Alviniconcha boucheti, black snail Ifremeria nautilei, and vent mussel Bathymodiolus sp. showed different carbon fixation pathways or nutrient preferences. We also observed niche partitioning among the omnivores by utilizing different resources or by occupying different microhabitats. For example, the squat lobster Munidopsis spp. occupied the bottom part of the chimney where dead shells were scattered around, as it was predatory to mussels. The scale worm Branchinotogluma segonzaci exploited energy from particulate organic matter or free-living bacteria on the chimney, whereas shrimp Rimicaris variabilis, which were clustered around I. nautilei and Echionelamus ohtai communities, had isotopic compositions similar to them. In contrast, limpets attached to I. nautilei did not share resources with snails and derived energy from mixed carbon sources. Among the vent fauna that we sampled, the crab was the top predator in the NFB, possibly consuming everything but with a lower preference for mussels. Overall, we found a non-overlapping diet or spatial niche of the vent fauna, with each taxon having a unique source or metabolism, or proportion. Such diversification in resource use may play an important role in sustaining the coexistence of species in a small area. [ABSTRACT FROM AUTHOR]