Search Results (78)

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

Helium-rich unconventional natural gas resources have attracted increasing attention from both academia and industry. A pronounced local enrichment of helium has recently been identified in coal-derived unconventional natural gas in the Sanjiaobei block on the eastern margin of the Ordos Basin. To clarify the main controls on helium enrichment in unconventional natural gas in this area and to guide the exploration of helium-rich resources, this study systematically examines the source of helium, its transport carrier, multiphase fractionation processes, and enrichment and accumulation pattern in natural gas. The analysis is based on conventional gas composition, helium volumetric content, carbon isotopes, and noble gas isotopes (He, Ne, and Ar) measured from wellhead gas samples collected from 11 production wells in the block, together with the regional deep structural evolution and hydrogeological conditions. The results show that: (1) the helium volumetric content of natural gas in the study area ranges from 0.0175% to 0.214%, with an average of 0.108%, and most wells fall within the high-helium grade category; (2) the helium isotope ratios ³He/⁴He (R/Ra) of the samples range from 0.0148 to 0.0824, indicating a typical crustal helium source; the good positive correlation between helium and nitrogen volumetric contents suggests that the two components share a highly consistent source affinity or common migration and accumulation behavior during fluid evolution; and the extremely high He/Ne ratios, on the order of 10⁴, together with excess Ar isotopes, indicate that the gases experienced little dilution by shallow atmospheric water or modern atmospheric fluids during migration and accumulation. The formation of helium-rich unconventional gas reservoirs on the eastern margin of the Ordos Basin is interpreted to be characterized by basement-derived helium supply, activation by tectonothermal events, groundwater transport, efficient fault-controlled migration, reservoir capture along migration pathways, and sealing by stagnant groundwater and lithologic barriers. On this basis, a helium enrichment model is established. This model depicts the geochemical evolution pathway of trace noble gases in a natural gas system and may provide a useful reference for helium resource evaluation in analogous areas. Full article

Hangzhou Bay has long experienced excessive nitrogen loading coupled with limited hydrodynamic exchange, leading to some of the highest nitrogen concentrations in China’s coastal waters. As critical land-sea ecotones, intertidal wetlands play a crucial role in mitigating nitrogen pollution across the bay. However, rapid urbanization and extensive reclamation since 1990 have led to a loss of over 50% of the intertidal wetlands in southern Hangzhou Bay. In this study we measured sediment denitrification and anammox potentials across key habitats: salt marshes (vegetated by Spartina alterniflora, Phragmites australis, and Scirpus mariqueter), bare mudflats, and shellfish aquaculture zones. We used ¹⁵N isotope tracing techniques coupled with slurry incubation experiments. Analysis of sediment physicochemical properties was conducted to elucidate the driving mechanisms of nitrogen removal. By integrating wetland landscape evolution with regional nitrogen budgets, we evaluated the nitrogen sink function of these intertidal wetlands. Our results revealed a distinct spatial hierarchy in denitrification potential, decreasing in the order: S. alterniflora (13.02 ± 3.54 μmol·N·kg⁻¹·h⁻¹) > shellfish aquaculture zones (12.86 ± 7.50 μmol·N·kg⁻¹·h⁻¹) > P. australis (11.54 ± 1.80 μmol·N·kg⁻¹·h⁻¹) > S. mariqueter (7.33 ± 2.08 μmol·N·kg⁻¹·h⁻¹) > bare mudflats (5.99 ± 1.62 μmol·N·kg⁻¹·h⁻¹). S. alterniflora has higher primary productivity, biomass accumulation, and a more robust root system structure. It regulates the content and availability of sediment organic carbon, the supply of nitrate nitrogen, pH, and water content. These regulations subsequently enhance denitrification. In contrast, shellfish aquaculture zones enhance denitrification potential primarily through bioturbation, which increases water content and lowers pH conditions. An integrated assessment of denitrification potential and landscape patterns revealed that, despite ongoing habitat loss, the remaining intertidal wetlands in southern Hangzhou Bay still remove about 30.65% of exogenous inorganic nitrogen. This finding underscores their critical role as effective pollution buffers under high nitrogen loading. Full article

Despite a plethora of studies in recent years focusing on the impact of nitrogen source addition on plant responses, there remains a lack of clarity regarding the differential utilization and distribution patterns of various nitrogen sources by Larix olgensis A. Henry seedlings. Specifically, the mechanisms by which ammonium nitrogen, nitrate nitrogen, and urea are differentially absorbed and distributed among different organs within the plant, as well as how these processes couple with rhizosphere soil microbial processes, still await elucidation. This study, conducted under field experimental conditions, employed a combination of ¹⁵N isotopic tracing, soil physicochemical property measurements, enzyme activity analysis, and microbial community functional analysis to investigate the effects of three nitrogen sources (NH₄⁺, NO₃⁻, and urea) and their varying addition levels on nitrogen absorption and distribution in Larix olgensis A. Henry seedlings. The results indicate that nitrogen source type significantly influences the nitrogen absorption rate and internal distribution patterns of plants. Within 24 h, seedlings preferentially absorb ammonium nitrogen and retain a higher proportion of newly absorbed nitrogen in their roots. The high ammonium chloride (GN) treatment group exhibited the highest ¹⁵N abundance in the root region, suggesting rapid root assimilation and short-term underground retention. By 48 h, the ¹⁵N abundance and AT% values in most organs across different treatment groups were significantly higher than those at 24 h, facilitating the transport of nitrate nitrogen and urea to stems and leaves, indicating a gradual shift in nitrogen distribution towards the aboveground parts. Moderate nitrogen addition improved soil nutrient conditions, altered pH and conductivity, enhanced nitrogen transformation processes related to urease and nitrate reductase, and increased microbial diversity and metabolic functions related to carbon metabolism, nitrogen metabolism, and energy metabolism. Soil pH, total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), and organic carbon (OC) are core environmental factors driving the differentiation of soil microbial community structure, with distinct specificity in the response of microbial groups across different taxonomic levels to soil physicochemical properties. Full article

Revitalisation of contaminated brownfield sites is essential for sustainable development, particularly near sensitive ecological areas like Natura 2000 sites. The lagoon in Slovenia’s Regional Park Šturmovci, an artificial wastewater convergence point created during hydroelectric construction, is a highly relevant example. This study integrates geochemical, mineralogical and isotopic analyses to identify sources and controlling mechanisms of contaminant distribution in lagoon sediments and assess their transfer to nearby agricultural soils during flooding events. Results indicate anaerobic conditions, with depth-related shifts in phosphorus, sulphur and redox-sensitive elements, such as rare earth elements (REE), arsenic (As), barium (Ba), cobalt (Co), chromium (Cr), lead (Pb) and vanadium (V), as well as fluctuations in pyrite-rich laminated layers, suggesting potential flood-driven remobilisation of trace elements. Lagoon sediments are highly contaminated with As (73 mg kg⁻¹), Ba (247 mg kg⁻¹), Pb (97 mg kg⁻¹) and Zn (1118 mg kg⁻¹), with elevated concentrations also observed in agricultural soil, all exceeding respective limit values of 20, 160, 85 and 200 mg kg⁻¹. Pollutant concentrations were highest near wastewater inflows and decreased with distance, with nitrogen isotopic patterns indicating partial nitrification and surface ammonium accumulation, reflecting intensive agricultural inputs in the area. High enrichment factor (EF > 20) and geoaccumulation index (I_geo > 3) values, in particular for As, Cd and Zn, indicated severe contamination and highlighted the urgent need for effective remediation strategies, including immobilisation using biochar or cement-based binders, as well as phytoremediation approaches. Full article

Sustainable rice production necessitates innovative strategies optimizing productivity while minimizing environmental impacts. This study developed and evaluated a Methodical Nitrogen–Water Distribution (MNWD) system, employing ¹⁵N isotopic tracing to quantify the fate of nitrogen under three management regimes: Farmer’s Practice (FP), Nitrogen–Water Coupling (NWC), and MNWD. Among them, NWC is conventional N–water coupling management, while MNWD is optimized management with reduced N, saved water and synchronous N–W uniform application. Two-year field experiments (2019–2020) demonstrated that MNWD achieved yield increases of 9.01–15.60% over FP and 2.51–5.73% over NWC, while reducing nitrogen application by 20%. Based on ¹⁵N tracing, the nitrogen recovery efficiency of MNWD reached 52.9–56.6%, and leaching losses were reduced by 65.4% compared to FP. The modular design of MNWD requires only moderate increases in labor input and basic fertigation infrastructure, ensuring its applicability to smallholder systems. The trade-off between emissions and efficiency confirmed the environmental benefits of MNWD: it resulted in 34.0% lower N₂O emissions than NWC while achieving a 5.45–5.49 percentage-point higher nitrogen recovery efficiency. Relative to FP, MNWD reduced total nitrogen losses by 48.5–61.4% with only a 3.4% increase in N₂O emissions. This indicates that nitrogen conservation was predominantly achieved through enhanced plant uptake rather than conversion to alternative loss pathways. The MNWD system demonstrates a viable pathway for sustainable rice intensification by successfully decoupling productivity gains from nitrogen input intensity. Full article

To elucidate the regulatory mechanisms underlying the interaction between straw return and nitrogen (N) fertilization on yield formation, nutrient uptake, and soil N cycling in a continuous maize cropping system, a two-year positioning experiment was conducted. The study established two straw treatments (S0: 0 g/box; S1: 84 g/box) combined with three N levels (N0: 0 g/box; N1: 1.24 g/box; N2: 2.47 g/box). (The box refers to the cylinder used for planting maize.) The responses of maize yield, plant nutrient accumulation and partitioning, fertilizer-derived N ratio, nitrogen fertilizer use efficiency (NUE), and soil microenvironment were analyzed. Results indicated that under N1 conditions, straw return had a negligible effect on crop growth and yield formation. Conversely, under N2 conditions, straw return significantly enhanced maize yield and promoted the accumulation of N, phosphorus (P), and potassium (K) in plant tissues. ¹⁵N isotope tracing revealed a novel mechanism: rather than significantly altering direct fertilizer nitrogen use efficiency, straw return improved crop yield primarily by elevating indigenous soil N content and boosting the activities of N-transforming enzymes, thereby beneficially altering the ultimate environmental fate of the fertilizer N. Furthermore, straw return significantly boosted the activities of enzymes involved in N transformation and optimized the soil microenvironment. Collectively, straw return coupled with increased N application (specifically the S1N2 treatment) significantly maximizes maize yield, providing a theoretical basis for rational straw utilization and N management. Full article

The widespread use of conventional plastic mulch films in agriculture contributes significantly to soil pollution due to their non-biodegradable nature. This study explores the potential of novel bio-based mulch films composed of chitosan, carboxymethyl cellulose, and sodium alginate, formulated in different ratios (1:1 and 17:3), with or without enrichment with monoammonium phosphate (MAP), to serve as biodegradable films with potential nutrient-releasing functionality as alternatives to conventional plastics. A multi-analytical approach, including elemental and isotopic analysis (EA-IRMS), biodegradation assays, and pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS), was employed to assess their chemical properties, degradation behavior, and environmental compatibility. The results demonstrated that the 1:1 films, both with and without MAP, achieved over 90% biodegradation within 120 days under controlled soil conditions, in agreement with international criteria for soil biodegradability. In contrast, the 17:3 films showed reduced degradation, especially without MAP enrichment, highlighting the influence of polymer composition on microbial degradation. Isotopic tracing confirmed MAP integration and revealed composition-dependent fractionation effects. Py-GC-MS provided structural fingerprints of film components and putatively annotated nitrogen-containing compounds indicative of chitosan presence. Overall, these results demonstrate that the 1:1 films can be considered viable, multifunctional, and soil-friendly alternatives to conventional plastic mulches for sustainable agriculture. 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

Atmospheric nitrogen deposition is increasing worldwide, with profound implications for plant nitrogen acquisition and ecosystem nutrient cycling, particularly in nitrogen-limited systems. In this study, we investigated how inorganic nitrogen form regulates nitrogen uptake in H. altissima through pot experiments by applying ammonium nitrogen, nitrate nitrogen, mixed nitrogen, and a nitrogen-free control in Songnen grassland ecosystems at the eastern end of Eurasia. Soil abiotic properties, root morphological traits, and nitrogen uptake dynamics were jointly quantified using integrative modeling in combination with ¹⁵N stable isotope tracing. Relative to the no-nitrogen control, both ammonium and nitrate nitrogen significantly altered soil physicochemical conditions and stimulated root development, with ammonium consistently exhibiting stronger effects. Ammonium and nitrate applications reduced soil pH by 4.83% and 6.25%, increased electrical conductivity by 2.01% and 1.17%, and enhanced inorganic nitrogen pools by 115.84% and 45.69%, respectively. Root morphological traits were significantly enhanced under ammonium, nitrate, and mixed nitrogen treatments. ¹⁵N tracing further demonstrated that ammonium nitrogen significantly increased root ¹⁵N uptake compared with the no-nitrogen control (p < 0.05) and promoted a 20.10% greater allocation of absorbed nitrogen to aboveground biomass than nitrate nitrogen. Collectively, these findings highlight nitrogen form as a key regulator of soil–plant nitrogen coupling, with ammonium nitrogen more effectively enhancing nitrogen acquisition and internal translocation than nitrate. Full article

Understanding how supplemental nitrogen (N) interacts with biological N₂ fixation (BNF) in modern soybean cultivars is essential for designing fertilization strategies that avoid unnecessary N inputs. We investigated N partitioning among soil, fertilizer and symbiotic sources in soybean grown in a greenhouse pot experiment on a tropical Oxisol. Plants were inoculated with Bradyrhizobium and subjected to four N managements: no external N, soil-applied ¹⁵N-urea (20 kg N ha⁻¹), foliar ¹⁵N-urea (2 kg N ha⁻¹, 0.7% w/v), and the combination of soil + foliar N. Using ¹⁵N isotope dilution, we quantified N derived from the atmosphere (NDFA), fertilizer (NDFF) and soil (NDFS) at organ and whole-plant scales, and related these fractions to nodulation, nitrogenase activity and yield. In the absence of external N, NDFA exceeded 97% in all organs, indicating a strong reliance on BNF and efficient internal N remobilization during grain filling, accompanied by higher leaf nitrate reductase activity. Soil and soil + foliar N markedly increased NDFF and NDFS while suppressing nodulation (particularly at V4) and reducing nitrogenase activity, yet they did not improve grain yield or vegetative biomass. Foliar N alone had only modest effects on N partitioning and did not enhance yield. Under these tropical soil conditions, symbiotic fixation and internal N remobilization were sufficient to meet grain N demand, highlighting the limited agronomic benefit and potential ecological cost of supplemental N during reproductive growth. Full article

This study focused on proteins derived from beef to minimize the influence of seasonings when developing a method for determining the geographical origin of seasoned beef samples. The seasoning used was sweetened soy sauce containing sugar, soy sauce, mirin and sake. The water-soluble fraction was extracted as a cleaning step for the sample, followed by extraction of the myofibrillar protein fraction. No significant differences were observed in the carbon, nitrogen and oxygen isotope ratios of the proteins extracted from the defatted raw and cooked beef samples. The carbon, nitrogen and oxygen isotope ratios of the protein fraction extracted from defatted beef were positively correlated with the corresponding ratios in the defatted whole beef samples. These results suggest that the protein fractions were mainly composed of beef proteins, and that the addition of auxiliary materials did not affect this. To verify the possibility of determining the geographic origin of beef, the carbon, nitrogen and oxygen isotope ratios of proteins extracted from beef from the United States (U.S.), Australia and Japan were analyzed. The carbon isotope ratios of proteins extracted from U.S. beef were higher than those of Australian and Japanese beef. Additionally, the oxygen isotope ratios of proteins extracted from Australian beef were higher than those of beef from the U.S. and Japan. These results suggest that it may be possible to trace the geographical origin of beef products cooked with seasonings by extracting proteins. Full article

Foxtail millet (Setaria italica (L.) P. Beauv.) exhibits varying efficiency in utilizing different nitrogen (N) forms. While selecting the appropriate N form is a recognized strategy for enhancing yield and reducing N losses, the integrated responses of millet productivity and soil N dynamics to specific N forms remain poorly understood. To address this, a three-year field experiment integrated with ¹⁵N isotopic tracing was conducted on the North China Plain. We systematically evaluated six fertilization treatments: control (CK), organic fertilizer (M), ammonium sulfate (AF), potassium nitrate (NF), ammonium nitrate (ANF), and urea (UR). The results demonstrated that M showed the greatest yield stability but a lower mean grain yield. In contrast, AF treatment achieved the highest grain yield (increasing by 0.90–27.68%) and N accumulation (increasing by 1.65–41.45%), along with the second-highest yield stability. During the growing season, the composition of soil inorganic nitrogen changed significantly. Across all treatments, the dominant form shifted from NH₄⁺-N at the heading stage to NO₃⁻-N at the flowering and maturation stages. As demonstrated by the ¹⁵N-labeling experiments, foxtail millet presented a stage-dependent shift in nitrogen uptake preference from NO₃⁻ to NH₄⁺. An in-depth analysis identified that sustaining soil inorganic N within 30–38 kg·ha⁻¹ and optimizing the NO₃⁻:NH₄⁺ ratio (4.5–5.3 at flowering; 1.5–1.8 at maturity) were critical for achieving high productivity. In conclusion, AF enhances yield by synchronizing N availability with crop demand, thereby optimizing N accumulation and reducing losses. These findings provide critical insights for designing sustainable millet production systems through tailored N source selection. Full article

Geographical origin determination for seafood products is a fundamental aspect due to its implications for fraud prevention, ensuring food safety, and promoting resource sustainable management. In this research, different machine learning (ML) models based on random forests, support vector machines, and artificial neural networks were fed with trace element fingerprinting (TEF) and stable isotope ratio analysis (SIRA) to determine the origin of mussels that have been farmed in eight regions and ten locations around the world (areas of the European Atlantic coast, the Mediterranean Sea, and the Pacific coast of Chile). Fourteen trace elements in shells and carbon and nitrogen isotope ratios of mussel tissue were used singly, in combination, or reduced to develop the different approach models. All the selected models present high prediction accuracies for the independent variables (except for SIRA models), for their combination, or for their optimisation, highlighting the artificial neural network and random forest models that presented a 100% accuracy for all cases using a combination of variables selected based on a random forest model TEF to predict region and location, respectively. This fact confirms that ML models are suitable approximation techniques to determine the region and location of Mediterranean mussel origin, with key applications in food safety and global sustainability. Full article