Search Results (553)

Background: The isotopic composition of the body’s internal environment can affect its functional state. Such effects are realized, among other things, by inserting deuterium atoms into hydrogen bonds between pairs of nitrogenous bases of DNA molecules and modifying their mechanical properties. Methods: This study uses a coarse-grained mathematical model of DNA. Results: It has been established that in a certain range of the magnitude of the torque, with the presence of a deuterium atom within it, stabilization of the CAG repeat tract is observed. In addition, it was found that, regardless of which base pair the deuterium atom falls into in the CAG repeat tract, its stability increases and the probability of hairpin formation decreases, which may interfere with the reading of genetic information from the site encoding glutamine. Conclusions: Single H/D substitutions in the CAG repeat tract of the ATXN2 gene increase its stability by reducing the formation of open states, regardless of the position of deuterium. Full article

Cobalt, molybdenum, and nickel are elements directly involved in biological nitrogen fixation in legume plants. However, there is a lack of information about the effects of the interaction among these elements on seed vigor and plant development. This study aimed to evaluate the effects of different doses of these elements on soybean seeds with higher and lower vigor, focusing on nitrogen metabolism and plant development under controlled conditions. The two lots of soybean seeds (higher and lower vigor) were treated with doses of 0, 2, 4, 6, and 8 mL kg⁻¹ of seeds of a liquid commercial product composed of cobalt, molybdenum, and nickel. At the full flowering stage, urease and nitrogenase activities, dry biomass of shoots, roots, and nodules, nitrogen concentration in shoots, plant height, number of nodules, and the efficiency of biological nitrogen fixation (measured by nitrogen-15 isotopic ratio) were assessed. Urease activity increased by 191% in high-vigor seed plants and 65% in low-vigor seed plants. Nitrogenase activity was higher in higher-vigor plants. Nodule dry biomass increased by 42% in lower-vigor plants compared to the control treatment, while in higher-vigor plants, it decreased with increasing doses. Shoot biomass was 30% higher than the control at the 2 mL kg⁻¹ dose. In general, the best responses to the application of the elements in the evaluated variables were observed with the doses of 2 and 4 mL kg⁻¹. It is concluded that the appropriate application of cobalt, molybdenum, and nickel on seeds enhances growth and symbiotic efficiency. However, excessive doses may cause phytotoxic effects. Full article

Water scarcity has become a significant constraint to agricultural development in China. In this study, we employed bibliometric methods to systematically review the current research on crop water use efficiency (WUE) and the development trends in the North China Plain (NCP) and Northwest China (NWC). We analyzed 1569 articles (NCP = 788; NWC = 781) from the Web of Science Core Collection (1995–2025) using visualization tools such as CiteSpace and VOSviewer to investigate annual numbers of publications, leading scholars and research institutions, and then to map keyword co-occurrence and co-citation structures. Our results showed that keyword clustering exhibited high structural quality (NCP: Q = 0.7345, S = 0.8634; NWC: Q = 0.758, S = 0.8912), supporting reliable thematic interpretation. The bibliometric analysis indicates a steady growth in annual publications since 1995, with the Chinese Academy of Sciences and China Agricultural University as leading contributors. From 1995 to 2005, studies centered on irrigation, yield and field-scale WUE, emphasizing the optimization of irrigation strategies and crop productivity. During 2006–2015, the thematic focus has broadened to encompass nitrogen use efficiency, crop quality and eco-environmental performance, thereby moving toward integrated evaluation frameworks that capture ecological synergies. Since 2016, the literature now emphasizes system integration, regional adaptability, climate-response mechanisms and the ecological co-benefits of agricultural practices. Future studies are expected to incorporate indicators such as crop quality, water footprint and carbon isotope indicators to support the sustainable development of agricultural water use. This study offers insights and recommendations for developing a comprehensive crop WUE evaluation framework in China, which will support sustainable agricultural water management and the realization of national “dual carbon” targets. Full article

This study aimed to determine how spatial and seasonal variations influence the trophic structure of fish assemblages in the eastern Yellow Sea during 2023. Carbon and nitrogen stable isotope analyses revealed significant but spatially variable differences in δ¹³C and δ¹⁵N values among seasons and sites, without consistent overarching trends. These results suggest that phytoplankton-derived organic matter predominantly supports the regional food web, with isotopic niche shifts reflecting local differences in prey availability and hydrographic conditions. The findings contribute to the development of adaptive, ecosystem-based fishery management strategies amid increasing anthropogenic and climatic pressures. Full article

This study investigates, for the first time, the relationship between carbon (δ¹³C) and nitrogen stable isotopic composition of Aspergillus niger mycelium, used as chitin and chitosan sources, and the fungus diet under controlled cultivation conditions. Four diets were tested, combining different carbon (C3- and C4-glucose) and nitrogen sources (KNO₃ and NH₄Cl). Results showed that carbon sources significantly influenced δ¹³C values of the mycelium: C4-glucose diets led to more negative Δ¹³C values (δ¹³C_MYCELIUM-δ¹³C_DIET) compared to C3-glucose diets. Nitrogen sources also affected isotopic fractionation, with KNO₃ leading to negative Δ¹⁵N (δ¹⁵N_MYCELIUM-δ¹⁵N_DIET) and NH₄Cl yielding positive Δ¹⁵N. Conversely, pH and temperature showed negligible effects on δ¹⁵N, while continuous aeration during growth significantly decreased δ¹⁵N, possibly due to partial assimilation of atmospheric nitrogen. These findings demonstrate that both nutrient and cultivation parameters can modulate the isotopic fractionation in A. niger, particularly for nitrogen. Although a direct correlation between diet composition and δ¹⁵N could not be established, this work provides the first experimental link between fungal metabolism and its isotopic fingerprint. The results offer a scientific foundation for applying stable isotope ratio analysis to authenticate and trace fungal-derived chitin and chitosan, with potential applications in food and winemaking industries. Full article

Soybean inoculation with nitrogen (N) fixing bacteria can be highly promising for enhancing biological nitrogen fixation (BNF) and improving crop productivity. It helps to reduce dependency on chemical fertilizers, promotes sustainable agricultural practices, and minimizes environmental impacts. Therefore, understanding the specific aspects and conditions is essential for establishing the BNF process in particular environments. In this study, we investigated whether soybean inoculation is an effective strategy in cool-climate regions beyond their typical northern distribution, and which soybean varieties and microbial strains are the most effective for optimizing soybean productivity and performance in relatively cool environments. To address these questions, a natural abundance nitrogen stable isotope ratio analysis was conducted on two soybean varieties of different maturity groups, which were inoculated with three Bradyrhizobium japonicum strains, along with organic fertilizer and new promising endophyte treatments. This approach aimed to determine the differences in biological and chemical parameters of soybean, as well as the origin of N sources, its uptake, and the isotopic distribution within the plants. It was demonstrated that inoculation with Bradyrhizobium japonicum was more effective than fertilization, as the strains had a significant effect on nitrogen derived from the atmosphere (Ndfa), produced stable nitrogen isotope ratios close to 0‰, and substantially increased nitrogen content, particularly in beans. Soybean varieties Laulema and Merlin, representing different maturity groups, exhibited distinct nitrogen uptake patterns. Bradyrhizobium japonicum strain AGF78 consistently produced the greatest effect on biological parameters in both varieties, particularly in seed yield and grain weight, with the later-maturing Merlin achieving the highest average yield of 3066.89 kg ha⁻¹. Notably, the Merlin inoculated with AGF78 resulted in the highest nitrogen fixation in beans, with 66.8%NDFA and 134.0 kg/ha of fixed nitrogen. Similarly, Laulema inoculated with AGF78 resulted in 88.2%NDFA and 123.2 kg/ha of fixed nitrogen. Inoculation with selected bacterial strains significantly increased protein content from 30% to 41%, with the effects being both strain- and variety-specific. Our study showed that establishing effective soybean–microbe interactions by choosing soybean variety and microbial strain is crucial for optimizing agricultural practices and improving crop performance, especially in sustainable and environmentally conscious farming systems under cool climatic conditions of Europe. Full article

The Yellow River (YR) has the highest suspended sediment concentration in the world, with its water and sediment exerting a significant influence on nutrient transport and transformation processes. The periodic regulation of water and sediment by the Xiaolangdi Dam, has significantly altered downstream water and sediment transport. This study examined the impact of the Xiaolangdi Dam’s 2023 water-sediment regulation on nitrogen dynamics in the lower Yellow River (LYR). Surface water, suspended sediment, and deposited sediment samples were collected at seven downstream stations to analyze changes in nitrogen concentration, sources, and transformation processes. As the water regulation stage progresses, the (total nitrogen) TN concentration in the water phase decreased, while that of NO₃^--N increased slightly. Concurrently, the inorganic nitrogen concentration in the suspended phase also declined. As the sediment regulation stage progresses, the TN and NO₃⁻-N concentrations in the water phase continued to decrease, while the inorganic nitrogen concentration in the suspended phase showed an initial increase followed by a decrease. As the early stage of sediment regulation progresses, ammonia concentrations decreased, while nitrate concentrations increased and δ¹⁸O-NO₃⁻ value decreased indicated nitrification occurred. As the late stage of sediment regulation progresses, nitrate concentrations decreased and the δ¹⁵N-NO₃⁻ value increased, indicated denitrification occurred. The TN flux during water-sediment regulation reaches 41.5 kt (14.6% of the annual flux). During the water-sediment regulation stage, the main nitrate sources were manure and sewage. This contribution peaked at 54.2% during the sediment regulation stage. The research results provide a scientific basis for the relationship between water and sediment changes and nitrogen output changes in the LYR. Full article

Background: Cervical lymph node metastases are a major prognostic factor in patients with oral squamous cell carcinoma (OSCC). Despite advances in imaging, accurate preoperative prediction of nodal involvement remains a challenge. This study evaluated the utility of Isotope Ratio Mass Spectrometry (IRMS) in assessing the risk of lymph node metastases in patients with OSCC. We hypothesize that alterations in the abundance of ¹³C and ¹⁵N stable isotopes in OSCC tumor tissues reflect metabolic reprogramming associated with tumor progression and may correlate with cervical lymph node metastases. Methods: A prospective cohort of 61 patients with primary OSCC undergoing surgical treatment was analyzed. Tumor tissue samples were evaluated for the relative abundance of nitrogen-15 (¹⁵N) and carbon-13 (¹³C) isotopes using IRMS. Correlations between isotopic values and nodal metastases, as well as established clinicopathological risk factors, were assessed. Results: IRMS measurements of ¹³C and ¹⁵N abundance did not directly correlate with the presence of lymph node metastases but were associated with advanced tumor stages and negative prognostic features, such as angioinvasion/neuroinvasion. The median of the average nitrogen ¹⁵N content was higher in patients with more advanced clinical stages (11.89% in stage IV vs. 11.12% in stages I–III; p = 0.04‰), and the median δ¹³C was lower in stage IV compared to stages I–III (−22.40‰ vs. −22.88‰; p < 0.05). Patients with angioinvasion/neuroinvasion also had a lower median δ¹³C (−22.26‰ vs. −22.75‰; p < 0.05). These findings suggest that IRMS reflects metabolic changes in tumor biology rather than specifically predicting nodal metastases. Multivariate logistic regression identified age, gender, and clinical tumor stage as independent predictors of nodal involvement. Conclusion: IRMS-based isotopic profiling may reflect key metabolic alterations associated with OSCC progression. Although IRMS parameters of carbon ¹³C and nitrogen ¹⁵N were not independently predictive of lymph node status, they were associated with key adverse prognostic features, indicating their potential as adjunctive biomarkers that may complement traditional histopathological evaluation. Full article

Topsoil degradation poses a significant threat to agricultural production worldwide. However, whether degraded topsoil is a net nitrogen source or sink depends on crop uptake and nutrient loss, and how it affects the sustainability of agricultural production remains unclear. To fill this gap in understanding, we conducted a three-year experiment with five topsoil depth treatments: 10 cm (D10), 20 cm (D20), 30 cm (D30), 40 cm (D40), and 50 cm (D50). Increasing topsoil depth significantly increased grain yield by a maximum of 49.4% (between D10 and D50). With increasing topsoil depth, the NFUE rises from 14.2% to 64.9% (between D10 and D50 treatments), while the G-NFUE climbs from 9.0% to 36.2% (between D10 and D40 treatments). Increasing topsoil depth reduced topsoil N depletion and the percentage of change in soil N stocks. In addition, N fertilizers applied during the season were generally enriched in soil at a depth of 30–40 cm. Therefore, increasing the depth of topsoil can effectively increase the source of nutrients absorbed by a crop by increasing access to additional resources stored in deeper soils, which ultimately increases maize grain yield and N fertilizer use efficiency. In this study, the threshold for maize to achieve high yields and efficiency was a topsoil depth of 30 cm. This study elucidated the differences in maize grain yield and resource utilization at different topsoil depths and established a link with soil N characteristics, and thus, it will provide a theoretical basis for the sustainable management of topsoil. Full article

Excessive nitrogen export from lowland polders is a key contributor to cultural eutrophication in downstream aquatic ecosystems. This study investigated the spatiotemporal characteristics, migration pathways, and sources of nitrogen pollution in a typical polder system. Eight surface water sampling campaigns were conducted at 13 sites in Quyuan Polder, Dongting Lake, from 2022 to 2023, combining ArcGIS spatial analysis, multivariate statistics, and dual-isotope (δ¹⁵N-NO⁻), δ¹⁸O-NO₃⁻) techniques. Nitrate and ammonium nitrogen dominated the nitrogen pool, accounting for ~76% of total nitrogen. Concentrations were higher in the dry season (2.48 mg/L) than in the wet season (1.89 mg/L) and differed significantly among hydrological periods (p < 0.05). Within the polder, total nitrogen and ammonium nitrogen were elevated, whereas nitrate nitrogen was higher at the outlet, reflecting distinct nitrogen profiles along the hydrological gradient. Nitrogen transport patterns were largely consistent with flow direction, driven by both upstream inputs and in situ generation. Isotopic signatures indicated that nitrate originated mainly from ammonium fertilizer and soil nitrogen, with contributions from manure and sewage. These findings enhance understanding of nitrogen dynamics in lowland catchments and provide a scientific basis for targeted pollution control in polder waters. Full article

Micro-sprinkling fertigation, a novel irrigation and fertilization way, can improve the grain yield (GY) and nitrogen use efficiency (NUE) of winter wheat to meet sustainable agriculture requirements. In order to clarify the physiological basis behind the improvements, a field experiment with a split-plot design was conducted during the 2020–2021 and 2021–2022 growing seasons. The main plot encompassed two irrigation and fertilization modes, namely, conventional irrigation and fertilization (CIF) and micro-sprinkling fertigation (MSF), and the subplots included four nitrogen application rates (0, 120, 180, and 240 kg ha⁻¹, denoted as N0, N120, N180, and N240, respectively). Moreover, a ¹⁵N isotopic tracer experiment was performed to determine the distributions of nitrogen in the soil. Compared with those under CIF, the GY under MSF at N180 and N240 significantly increased by 9.09% and 9.72%, which was driven mainly by increases in the grain number (GN) and thousand-grain weight (TGW). The increase in the TGW under MSF was the result of the significantly increased net photosynthesis rate at the grain-filling stage. Notably, the number and dry weight of inefficient tillers and the number of ears with fewer than 10 grains were significantly lower under MSF than those under CIF. In addition, the ¹⁵N isotopic tracer experiment revealed that nitrogen was primarily concentrated in the 0–30 cm soil layers under MSF, which conforms well with the spatial distributions of the roots and water, and subsequently improved the NUE under N180 and N240. In conclusion, MSF enhanced both the GY and NUE at the N180 level by optimizing root–water–nitrogen spatiotemporal coordination and reducing redundant tillering. Full article

Static chambers combined with isotopic (δ¹³C and δ¹⁸O) and flux (CO₂ and CH₄) measurements were applied, to explore the effects of mosses and long-term nitrogen (N) addition at two levels (22.5 and 45 kg N ha⁻¹ yr⁻¹) on δ¹³C and δ¹⁸O values of respired CO₂ across three autumn seasons under a temperate forest (northeastern China) and their relationships with CO₂ and CH₄ fluxes and with soil properties. Mosses generally depleted δ¹³C and enriched δ¹⁸O in respired CO₂, likely by altering soil microenvironments or/and substrate use. The effect of N addition on the δ¹³C and δ¹⁸O values of respired CO₂ varied with years, and its interaction with mosses had no effects on the isotopic values. The removal of mosses decreased CO₂ fluxes and the addition of N at a high dose increased CH₄ fluxes. The δ¹³C and δ¹⁸O values of respired CO₂ decreased at soil moisture levels below and above an optimum, and the moisture-dependent effect became more pronounced for the δ¹⁸O than for the δ¹³C. The results of structural equation modeling showed that 70% of the variability of δ¹³C values of respired CO_2. was accounted for by the N addition, mosses, soil moisture, and CH₄ and CO₂ fluxes, while only 22% of the variability of δ¹⁸O values of respired CO₂ was explained by these factors. The results highlight that moss–soil interaction drives the isotopic shifts, which is modulated by N availability. Soil moisture regulates the δ¹⁸O values of respired CO₂, but its drivers remain poorly understood. Future work should target processes influencing the δ¹⁸O shifts of respired CO₂ and deep soil property interactions. Full article

Forest soil greenhouse gas emissions play a critical role in global climate change. This review synthesizes the mechanisms of temperature change impacts on forest soil greenhouse gas (CO₂, CH₄, N₂O) emissions, the complex response patterns of ecosystems, and existing knowledge gaps in current research. We highlight several critical mechanisms, such as the high temperature sensitivity (Q₁₀) of methane (CH₄) and CO₂ emissions from high-latitude peatlands, and the dual effect of chronic nitrogen deposition, which can cause short-term stimulation but long-term suppression of soil CO₂ emissions. It emphasizes how climatic factors, soil characteristics, vegetation types, and anthropogenic disturbances (such as forest management and fire) regulate emission processes through multi-scale interactions. This review further summarizes the advancements and limitations of current research methodologies and points out future research directions. These include strengthening long-term multi-factor experiments, developing high-precision models that integrate microbial functional genomics and isotope tracing techniques, and exploring innovative emission reduction strategies. Ultimately, this synthesis aims to provide a scientific basis and key ecological threshold references for developing climate-resilient sustainable forest management practices and effective climate change mitigation policies. Full article

Mixed legume–grass pastures may enhance nitrogen recycling via litter and excreta compared to unfertilized grass monocultures. This study evaluated litter biomass, litter deposition rate, and the chemical and isotopic composition of Urochloa decumbens litter in monoculture and mixed pasture intercropped with Arachis pintoi cv. Belmonte at five planting spacings (0.40, 0.50, 0.60, 0.70, and 0.80 m) in a Ferralsol. Additionally, isotopic analysis of sheep feces under grazing was conducted across the dry season. The experiment was conducted according to a split-plot scheme, with spacings in the plots and the periods or years in the subplots, in a randomized block design, with four replications. Litter biomass was not significantly influenced by planting spacing; however, the litter deposition rate was substantially greater in mixed pastures, reaching up to 77.2 kg ha⁻¹ day⁻¹ in the second year. Isotopic analysis revealed that up to 39% of the litter carbon was derived from C3 plants (Arachis pintoi), while nitrogen concentration ranged from 8.3 g kg⁻¹ in monoculture to 12.9 g kg⁻¹ at 0.40 m spacing. Spatial arrangement was critical for optimizing nutrients dynamic. Narrower planting spacings (0.40–0.50 m) increased the proportion of Arachis pintoi and enhanced litter deposition rates, improving nitrogen inputs and cycling within mixed Urochloa decumbens. Full article

This study aimed to examine how biochar and Acacia species would affect biological nitrogen fixation (BNF) and water use efficiency (WUE) of understorey Acacia species as well as soil carbon (C) and nitrogen (N) pools 15 months after biochar application in the suburban native forest of subtropical Australia. This experiment was established with wood biochar applied at 0, 5, and 10 t ha⁻¹ at 20 months after prescribed burning. We collected foliar and soil samples 15 months after biochar application and used N isotope composition (δ¹⁵N) and carbon isotope composition (δ¹³C) to assess the BNF and WUE of two understorey Acacia species (Acacia leiocalyx and Acacia disparrima). We also characterised soil C and N pools and their δ¹⁵N and δ¹³C. Biochar did not influence Acacia plant BNF and WUE 15 months after biochar application. However, the BNF of A. leiocalyx was significantly greater compared with that of A. disparrima. The soil under A. leiocalyx had greater NH₄⁺-N (i.e., 10–20 cm) but lower δ¹⁵N than A. disparrima. This study represents one of the few attempts to apply the ¹⁵N natural abundance (δ¹⁵N) techniques to quantify the soil–plant–microbe interactions for N cycling in a native forest ecosystem. Understorey A. leiocalyx was more effective in improving N recovery post-fire via BNF. Soil under A. leiocalyx had greater N availability with lower δ¹⁵N, influencing plant available N sources and δ¹⁵N. Thus, A. leiocalyx would be able to fix more N₂ from the air compared with that of A. disparrima in the suburban native forest ecosystem subject to periodical fuel reduction prescribed burning. Full article