Search Results (305)

Nitrogen oxides (NO_x), comprising nitric oxide (NO) and nitrogen dioxide (NO₂), are key precursors of atmospheric nitrate, a major component of fine particulate matter (PM_2.5) that critically affects air quality, human health, and ecosystems. Emission inventories provide detailed spatial and temporal information on NO_x sources, while stable isotope techniques offer an additional constraint for source apportionment. Here, we incorporated stable nitrogen isotopes (¹⁴N, ¹⁵N) into the widely used Multi-resolution Emission Inventory for China (MEIC) over South China, with a focus on the Pearl River Delta (PRD) region, one of the most highly urbanized and industrialized regions in China, using an isotopic mass–balance model. The 2008 MEIC inventory indicated that NO_x emissions across South China were spatially heterogeneous, dominated by transportation sources, and concentrated mainly in the PRD and other urban clusters. We then compared the simulated isotopic composition of emitted NO_x with atmospheric measurements to assess the role of emission sources in controlling atmospheric nitrate (NO₃⁻). The simulated δ¹⁵N(NO_x) values were found to generally underestimate the observed δ¹⁵N(NO₃⁻) values. This discrepancy highlights the need for future ¹⁵N-enabled air quality modeling to better represent both source contributions and atmospheric processing, thereby improving source apportionment, emission inventory evaluation, and our understanding of reactive nitrogen cycling. Full article

Tetrastigma hemsleyanum Diels et Gilg is a high-value edible and medicinal homologous plant, routinely grown under conventional field or greenhouse production systems across Asia. However, mislabeling of conventional products as the rarer (and more expensive) wild version may occur for financial gain. In this study, stable isotopes (δ¹³C, δ¹⁵N, δ²H, and δ¹⁸O) and metal contents (Cr, Cu, Ni, As, Cd, Pb) were used to characterize plant tissues (tuber root, stem, leaf) and corresponding soils originating from simulated-wild-cultivated (WC) and greenhouse-cultivated (GC) pot trials using the same soil. Carbon and nitrogen isotopes served as key indicators for distinguishing GC and WC products. Specifically, δ¹³C values of GC plant tissues were 1.4 to 2.4‰ more positive than those of WC plant tissues (p < 0.05), and δ¹⁵N values in GC tissues were 2.7 to 4.6‰ more positive than δ¹⁵N in WC tissues (p < 0.01). Lower δ¹⁵N values observed in WC products indicate slower nitrogen turnover compared with GC products. Soil metal concentrations had significant differences between the two cultivation systems, but only limited effects on metal bioconcentration factors (BCFs) and translocation factors (TFs) in T. hemsleyanum tissues. Pb and Cd concentrations in root tissues had large differences between cultivation systems, and carbon dynamics in GC plants were more negatively affected by Pb levels in soils. These findings provide the first investigation of T. hemsleyanum grown under different cultivation practices and establish a scientific basis for distinguishing other wild or simulated-wild labeled food and medicinal plant products from conventionally grown products in future studies. Full article

This study investigated spring water in the core area and buffer zone of the Shibing Dolomite Karst World Heritage Site using one-year monthly monitoring, hydrochemistry, nitrate dual isotopes, and the MixSIAR model. The buffer zone spring exhibits shallow fissure-conduit flow with rapid hydrological response, anthropogenic nitrate dominance (>62%), nitrification as the main process, and limited denitrification. Its nitrate concentration shows seasonal peaks. In contrast, the core area spring is recharged by deep fissure water, with natural nitrate sources (>80%), stable nitrate levels (5–7.4 mg/L), and potential local denitrification. Nitrogen export in the buffer zone increases 4.5 times in the rainy season (NO₃⁻ accounting for 93% of TN). The core area shows higher TN export flux per unit area (3.34 vs. 0.4 g/m²/a) and greater DON proportion. Nitrogen export far exceeds that from rocky desertified areas, suggesting that dissolved nitrogen leaching drives karst rocky desertification evolution. Full article

Background/Objectives: Oral squamous cell carcinoma (OSCC) exhibits substantial biological heterogeneity, and current clinicopathological risk stratification incompletely reflects tumor metabolic behavior. Stable isotope ratio mass spectrometry enables the quantitative assessment of carbon and nitrogen isotopic composition, potentially capturing cumulative metabolic reprogramming associated with tumor aggressiveness. This study evaluated whether isotopic signatures of tumor tissue and surgical margins are associated with lymph node metastasis and survival outcomes in OSCC. Methods: In this prospective study, 54 consecutive patients undergoing primary surgical treatment for OSCC were enrolled. Paired samples derived from tumor tissue and surgical margins were analyzed using isotope ratio mass spectrometry to determine the relative abundance of nitrogen-15 and carbon-13 isotopes. The primary endpoint was pathological lymph node metastasis. Secondary endpoints included disease-free survival and overall survival. Paired comparisons were performed using Wilcoxon signed-rank tests with false discovery rate correction. Logistic regression models for nodal metastasis were constructed using Firth penalization with bootstrap internal validation, while survival outcomes were evaluated using Cox proportional hazards models with model complexity restricted according to the number of events. Results: Tumor tissues demonstrated significantly lower δ¹³C and δ¹⁵N values and higher nitrogen-to-carbon ratios compared with surgical margins (all adjusted p < 0.05). In multivariable analysis, tumor δ¹⁵N was independently associated with lymph node metastasis and modestly improved model discrimination. However, it was not independently associated with disease-free or overall survival. Exploratory analyses indicated that higher δ¹³C values in surgical margins were independently associated with shorter disease-free survival. Conclusions: These findings suggest that isotope ratio mass spectrometry-based isotopic profiling identifies reproducible metabolic differences between tumor and margin tissues in OSCC. Tumor δ¹⁵N is associated with lymph node metastasis, whereas margin δ¹³C may reflect recurrence risk and potentially capture metabolic field effects. These findings are hypothesis-generating and warrant validation in larger, independent cohorts. Full article

To elucidate the sources and spatial variations in organic matter in surface sediments from Lingdingyang of the Pearl River Estuary, 18 surface sediment samples were collected and analyzed for obtaining total organic carbon (TOC), total nitrogen (TN), atomic TOC/TN ratio (C/N_atom), stable carbon and nitrogen isotopes (δ¹³C, δ¹⁵N), and glycerol dialkyl glycerol tetraethers (GDGTs). A three-endmember framework was constructed using the BIT and δ¹³C to constrain the sources of the organic matter. The results showed a significant positive correlation between TOC and TN, with relatively higher values in Jiaoyi Bay and western Lingdingyang, lower values in eastern Lingdingyang, and intermediate values in Shenzhen Bay. The C/N_atom, δ¹³C, and δ¹⁵N results revealed that the sedimentary organic matter in the study area exhibits mixed-source characteristics, influenced by soil, C₃ plants, and marine autochthonous organic matter. Among the subregions, Jiaoyi Bay is more strongly influenced by terrestrial inputs, while Shenzhen Bay receives relatively higher contributions from marine autochthonous organic matter. The GDGTs results showed that Jiaoyi Bay is characterized by elevated abundances of both brGDGTs and isoGDGTs, whereas isoGDGTs were also relatively enriched in Shenzhen Bay. brGDGTs exhibited a significant negative correlation with δ¹³C, whereas BIT showed no significant correlation with either brGDGTs or δ¹³C, indicating that BIT cannot be simply regarded as a unique proxy for soil input, but rather reflects the combined effects of in situ production, changes in archaeal lipids, and sedimentary preservation. The three-endmember model further revealed significant spatial variations in the sources of organic matter in surface sediments from Lingdingyang. Overall, the combined use of multiple proxies is more effective than any single proxy in revealing the sources and spatial differentiation of sedimentary organic matter in this subtropical, complex estuarine environment. Full article

Against the backdrop of global coral reef degradation, benthic resource structure is shifting from coral dominance to turf algae and detritus-dominated epilithic algal matrix (EAM). As a typical detritivorous reef fish, Ctenochaetus striatus (Quoy & Gaimard, 1825) plays an important ecological role in regulating the functioning of degraded coral reef ecosystems. Using stable isotope analysis (δ¹³C and δ¹⁵N), this study systematically compared the trophic niche characteristics of different size classes of C. striatus across four reef habitats in the Xisha Islands, South China Sea, representing a gradient of disturbance (Qilianyu Island > Lingyang Reef > North Reef > Langhua Reef), in order to elucidate habitat-specific ontogenetic shifts and their adaptive features. The results showed that C. striatus from Qilianyu Island and Lingyang Reef exhibited overall higher δ¹⁵N values, suggesting an overall pattern consistent with stronger nitrogen enrichment at the more disturbed reefs, whereas individuals from Langhua Reef had significantly lower δ¹³C values, indicating a stronger reliance on offshore-derived carbon pathways. Across size classes, the trophic niche area (SEAc) and intraspecific trophic heterogeneity, measured as mean nearest neighbor distance and standard deviation of nearest neighbor distance, of populations from Qilianyu Island, Lingyang Reef, and North Reef generally decreased with increasing body size, revealing a pattern of trophic convergence toward core resources. In contrast, the Langhua Reef population exhibited a distinct expansion–contraction pattern, suggesting flexible resource use across developmental stages under conditions of low human disturbance and high resource heterogeneity. Although smaller size classes generally showed high probabilities of niche overlap among reefs, overlap declined markedly in the largest size class, with most values falling below 50%, indicating that resource assimilation strategies increasingly reflected reef-specific resource backgrounds. These findings demonstrate that ontogenetic trophic niche shifts in C. striatus are not fixed, but are highly dependent on local resource context and habitat conditions. In degraded reefs with simplified resource structure, individuals tend to converge on core resource spectra to maintain survival, whereas in healthier reefs with greater habitat heterogeneity, they tend to show greater variation in major food sources and resource use. This study provides a theoretical basis for coral reef ecological restoration. Full article

The urea cycle (UC) is usually described as the hepatic metabolic pathway responsible for ammonia detoxification, but its role extends far beyond nitrogen (N) elimination to include cellular biosynthesis and metabolic signalling. In cancer cells, the UC is reconfigured/reorchestrated to support high anabolic demand, often involving the dysregulation of key enzymes such as ASS1, ASL, OTC and CPS1. While these changes support biomass production and stress resistance, they also generate measurable biochemical signatures through kinetic and thermodynamic isotope effects (¹⁴N/¹⁵N). In this review, we summarise UC biochemistry and recall key enzymatic mechanisms. Together, these elements provide a mechanistic framework to interpret changes in ¹⁵N abundance observed in tumour tissues and cells. We discuss how the redirection of N flux toward nucleotide and polyamine synthesis, coupled with partial excretion of ¹⁵N-depleted urea, may shape the isotopic composition of cancer cells. By integrating molecular oncology with stable isotope analysis, this review highlights the potential of natural isotope abundance as a functional readout of tumour metabolism and supports further investigation of its translational relevance in cancer phenotyping and monitoring. Full article

Although microbial communities in rice agroecosystems regulate nitrogen transformations, methane dynamics, crop residue decomposition, and pathogen suppression, their integration into agronomic decision-making remains limited. Existing rice microbiome reviews largely describe taxonomic diversity without critically linking microbial processes to management trade-offs, greenhouse gas mitigation, and productivity outcomes. This review synthesizes current knowledge through a process-based and management-oriented framework, emphasizing how water and crop residue management, fertilization, tillage, and genotype selection shape microbial functionality rather than merely community composition. Advances in stable isotope probing (SIP), metatranscriptomics, and multi-omics have improved functional inference, yet a persistent gap remains between genetic potential and in situ process rates. By integrating microbiome science within a One Health perspective, we propose a conceptual framework linking microbial network structure to interconnected dimensions of ecosystem, plant, and human health. This framework addresses not only agronomic outcomes but also food safety concerns, including mycotoxin contamination by fungal pathogens, microbial contributions to nutritional quality, and pathways through which soil and plant microbiomes influence human health via the food chain. We critically examine how microbiome management can simultaneously target productivity, environmental sustainability, and health risk mitigation. We identify priority research needs in predictive microbial ecology, activity-based validation, and microbiome-informed management strategies. Rather than framing microbiomes as a universal solution to global food security, this review critically examines their realistic and context-dependent contribution to improving sustainability, resilience, and resource-use efficiency in rice production under climatic and environmental constraints, while safeguarding food safety and public health. Full article

Microscopic green algae are active producers of beneficial compounds, particularly those containing nitrogen. However, the metabolism of nitrogen-containing compounds is diverse and depends on the conditions of the nitrogen source. As a result, the approach to studying the metabolism of nitrogen-containing compounds becomes more complicated. This work demonstrates the metabolic changes in the high-productive green algae Neochlorella semenenkoi IPPAS C-1210 under conditions of nitrogen starvation and subsequent reintake, using high-performance liquid chromatography–mass spectrometry (HPLC–MS) with ¹⁵N isotopic labeling. The presented results include semi-quantitative chromatography–mass spectrometric analysis for 17 amino acids, a metabolomic profile of over 40 isotopically labeled compounds, an assessment of metabolic flux via isotopic incorporation, and an analysis of cellular lipid composition under varying growth conditions. The findings indicate that this strain can utilize ammonium acetate as a nitrogen source, consuming nitrogen in the ammonium form. The degree of isotopic labeling in compounds often diverged significantly from their quantitative changes (concentrations and chromatographic peak areas), suggesting that isotopic analysis may offer advantages over purely quantitative analysis for biological systems. Furthermore, in vivo biological isotopic labeling is shown to assist in identifying compounds absent from standard mass spectrometric databases. Full article

Nitrogen isotopes have garnered increasing attention in the investigation of nitrogen (N) dynamics. However, there remains a significant knowledge gap concerning the dynamics of plant–soil nitrogen interactions and their driving factors under conditions of increasing groundwater depth. In this study, we assessed the response of soil and plant tissue ¹⁵N signatures of two dominant species (the herb Pennisetum centrasiaticum and the shrub Artemisia halodendron) to three groundwater depth treatments (30 cm, 50 cm, and 100 cm) with the addition of N compounds (¹⁵NH₄¹⁵NO₃) in the Horqin Sandy Land. Our results suggested that soil δ¹⁵N increased with soil depth at 30 cm groundwater depth, and plant tissue δ¹⁵N were positively related to soil δ¹⁵N at 30 and 50 cm groundwater depth. Negative effects of groundwater depth variability on plant tissue δ¹⁵N and TN values were observed; our results also showed that the variability in SW and pH caused by groundwater depth was most responsible for the distribution in plant tissue N. These findings enhance our understanding of the profound impacts of climate change on plant and soil properties and their interrelationships in semi-arid regions and also provide critical insights to underpin sustainable water resources management. Full article

Mollisols represent foundational agricultural soils in which high organic carbon (C) and active microbiomes sustain fertility and mediate global C cycling. However, decades of intensive cultivation have depleted soil organic C (SOC) and degraded soil structure and function. Enhancing C sequestration in agricultural Mollisols through the incorporation of organic residue, such as crop residues, organic waste, and spent mushroom substrates has become an urgent scientific and management priority. This review integrates advances from the past decade, combining stable isotope probing, multi-omics analyses, and ultrahigh-resolution molecular characterization to elucidate how microorganisms mediate C sequestration during organic residue return and decomposition. We propose a four-dimensional conceptual framework, “substrate–microenvironment–metabolic pathway–residue stabilization,” that links microbial metabolism with long-term C persistence in Mollisols. We further highlight that organic residue inputs promote CO₂ sequestration via fermentation–autotrophy coupling, nitrifying autotrophy, and microbial mixotrophy. Major C sequestration pathways operate synergistically across redox microenvironments, forming stratified metabolic networks that sustain continuous C cycling. The chemical composition and decomposition kinetics of organic residue governs substrate and energy fluxes for microbial C sequestration, while soil redox status, and nutrient coupling (Carbon–Nitrogen–Phosphorus–Sulfur) collectively direct C flow toward stabilization. Microbial necromass and extracellular polymers achieve long-term C storage through mineral adsorption and microaggregate formation. Finally, we summarize recent methodological advances for tracing microbial CO₂ sequestration in agricultural Mollisols and identify key research needs on residue formation, C use efficiency, and aggregate-mineral protection mechanisms. This synthesis establishes a mechanistic foundation for biologically regulated C management and offers guidance for sustainable cropland restoration. Full article

Monitoring the soil–plant system in forest ecosystems is crucial for preserving their ecological functions and services. This study assessed carbon and nitrogen stable isotopes and ecoenzymatic stoichiometry as suitable indicators for characterizing the soil–plant system as a functional unit of ecological processes. To this end, in June 2021 six plots (1 m² each) were selected in two typical Mediterranean forest ecotypes: a coastal stone pine forest (Pinus pinea L., PF) and a meso-hygrophilous broadleaf forest (RV). Soil samples (0–15 and 15–30 cm depth) and litter samples (40 × 40 cm) were collected and characterized in terms of physical, chemical and biochemical properties. t-tests revealed significant differences between RV and PF, indicating distinct microbial nutrient acquisition strategies. The higher C:N ratio in PF suggested lower litter quality and greater recalcitrance to microbial decomposition. Consistently, RV showed a more pronounced ¹³C and ¹⁵N enrichment from litter to SOM down to a 30 cm depth, confirming faster organic matter decomposition and mineralization. Enzyme activity patterns supported these findings. The higher β-glucosidase and butyrate esterase activities in RV reflected its greater microbial potential to activate biogeochemical cycles. Both forests exhibited a higher microbial demand for C and P than for N to maintain ecological stoichiometric balance, with stronger C limitation at the surface and P limitation in the subsoil, particularly in RV soil. This integrated monitoring approach provides insights into nutrient cycling and ecosystem resilience and offers tools to evaluate ecosystem functionality under changing environmental conditions, supporting sustainable forest management. Full article

Stable isotope analysis is very useful for studying animal nutritional ecology. Feces are the most accessible and non-invasive samples for short-term dietary reconstruction. The giant panda is a special Carnivora species with a highly specialized diet. However, no relevant research has yet explored the reliability of fecal isotopes in wild giant pandas, and the key parameter—fecal isotopic discrimination factors—remains unreported. Thus, we analyzed carbon and nitrogen isotopes of different bamboo species and parts with associated pandas’ feces collected from their foraging sites. The results showed carbon isotopes of shoots were more positive than those of leaves, and the isotopic composition of their feces can effectively reflect seasonal dietary shifts. The calculated fecal carbon discrimination factor was close to zero (Δ¹³C_diet-feces = 0.6 ± 0.8‰), while the nitrogen DFs were significantly positive (Δ¹⁵N_diet-feces = 2.1 ± 1.2‰). The typical metabolic pattern, physiological adaptations and distinctive microbiota of giant pandas contribute to the unique DFs different from those of other herbivores. These findings provide valuable short-term dietary records, key parameters for the application of fecal isotopes to interpret foraging strategies and nutritional status for an endangered species in the wild, expand the application of stable isotope methods in studies to specialized diet animals, and offer a reference for studies utilizing non-invasive materials in other mammals. Full article

Waterlogging stress, particularly during flowering, severely constrains wheat production, yet the optimal timing and frequency of waterlogging priming and its linkage to post-stress nitrogen acquisition remain unclear. We conducted pot experiments under a glasshouse over two consecutive growing seasons (2022/23 and 2023/24) using the Japanese bread wheat cultivar Norin 61. Eight treatment combinations were established with or without waterlogging priming applied at the tillering, stem elongation, and booting stages, followed by waterlogging for 5 days (2022/23) and 4 days (2023/24) during the flowering stage. To quantify post-stress nitrogen dynamics, ¹⁵N-labeled ammonium sulfate was applied immediately after waterlogging termination at flowering, and ¹⁵N uptake and its allocation to plant organs and grains were determined during grain filling and at harvest. Compared to the non-primed treatment, treatments that included tillering-stage priming consistently maintained higher leaf SPAD values, photosynthetic performance, and increased thousand-grain weight across both seasons, and grain yield increased by 54.8–80.6% in 2022/23 and 125.8–159.7% in 2023/24. These treatments also showed higher post-stress ¹⁵N content and greater ¹⁵N allocation to grains. Overall, tillering-stage waterlogging priming was associated with improved tolerance to flowering-stage waterlogging in wheat through the maintenance of post-stress nitrogen uptake capacity and nitrogen allocation to grains. Full article

Interest in seafood diet and health warrants a biomarker for seafood consumption. Nitrogen isotope ratio (¹⁵N/¹⁴N, expressed as δ¹⁵N (‰)) has been regarded as a biomarker for such a purpose. This study aims to elucidate the applicability of levels of arsenobetaine (AB), a non-toxic organic arsenic compound, in the diet as a marker of seafood abundance because of its known distribution in marine animals. The concentrations of AB and other arsenic species and δ¹⁵N in duplicate diet samples collected from 150 Japanese adults were analyzed for a possible relationship with the inclusion of seafood and seaweed in the diet samples. Information was collected from the menu reported from the duplicate diet donners, and a possible correlation between the levels of AB and δ¹⁵N was tested. As expected, median levels of AB and δ¹⁵N were more elevated in the duplicate diet that contained seafood (54.6 ng/g dry and 3.60‰) than that without seafood (<7 ng/g dry and 3.01‰). Additionally, there was a significant positive correlation between the two components (Spearman’s ρ = 0.384, p < 0.001). The distinct difference between the seafood-containing and non-containing diet suggested that the AB content of the diet is a more sensitive marker of seafood abundance than δ¹⁵N. Full article