Search Results (2,108)

The global deterioration of water quality due to climate change and industrialization has intensified the need for real-time monitoring systems. In South Korea’s automated water quality monitoring networks, measuring total organic carbon (TOC) and nitrate nitrogen (NO₃-N) as a proxy for total nitrogen (TN) is critical; however, conventional analytical instruments face limitations such as high costs, long analysis times, and the need for chemical reagents. In this study, we developed and evaluated a simultaneous TOC and NO₃-N measurement method using HASM-4000, a domestically developed optical sensor based on ultraviolet (UV) absorption spectroscopy. The sensor measures absorbance at 254 nm (TOC) and 220 nm (NO₃-N) based on the Beer–Lambert law, with signal processing techniques including optical power compensation (OPC) and Binning–Interpolation (BinInterp) applied to enhance measurement accuracy. Calibration using standard solutions demonstrated excellent linear correlations (R² > 0.99) between actual and estimated concentrations for both TOC and NO₃-N, with accuracy and reproducibility validated against standard methods under laboratory conditions. However, performance degradation was observed in turbid mixed samples due to the optical limitations of the 10 mm pathlength, suggesting the need for future improvements such as adopting a 5 mm pathlength and upgrading optical components. The HASM-4000 sensor enables real-time measurement without a reagent, and preliminary testing with river water samples demonstrates its potential to advance Korea’s water quality monitoring infrastructure by reducing dependence on foreign technologies and facilitating network expansion with cost-effective domestic solutions. Full article

The upper Xin’an River basin serves as a critical ecological barrier and water-conservation area for the Yangtze River Delta. However, with rapid economic development, nitrogen pollution in the surface waters of this region has become increasingly pronounced. This study analyzed river water samples collected on four occasions from the upper Xin’an River basin for ammonium (NH₄⁺–N), nitrate-nitrogen (NO₃⁻–N), total nitrogen (TN), and nitrate isotopic (δ¹⁵N–NO₃⁻ and δ¹⁸O–NO₃⁻). The sources of nitrate (NO₃⁻) were apportioned using the MixSIAR stable-isotope mixing model, and the spatial distribution of these sources across the basin was characterized. Across the four sampling rounds, the mean TN concentration exceeded 1.3 mg/L, with NO₃⁻–N accounting for over 45% of TN, indicating that nitrate was the dominant inorganic nitrogen species. The δ¹⁵N–NO₃⁻ values ranged from 2.17‰ to 13.0‰, with mean values following the order summer > winter > autumn > spring. The δ¹⁸O–NO₃⁻ values varied from −5.20‰ to −3.48‰, and the average value showed a completely opposite seasonal variation pattern to that of δ¹⁵N–NO₃⁻. Process-based analysis of nitrogen transformations revealed that nitrification predominates during nitrate transport and transformation, whereas denitrification is comparatively weak. MixSIAR-based estimates indicate marked seasonal differences in the source composition of nitrate pollution in the upper Xin’an River basin; NO₃⁻ derives primarily from soil nitrogen (SN) and livestock/sewage manure nitrogen (LSN). LSN was the dominant contributor in spring and summer (49.2% and 59.9%, respectively). SN dominated in autumn (49.2%) and winter (54.1%). Fertilizer nitrogen (FN) contributed more during summer and autumn, when fertilization is concentrated and rainfall is higher. Atmospheric deposition (AN) contributed approximately 1% across all seasons and was thus considered negligible. These findings provide a scientific basis for source control of nitrogen pollution and water-quality management in the upper Xin’an River. Full article

The simultaneous challenges of cadmium (Cd) contamination and mineral nutrient imbalance in paddy systems necessitate the development of effective agronomic strategies. This study systematically investigated the coordinated effects of different nitrogen fertilizer forms on the accumulation and translocation of Cd and mineral elements in rice. A hydroponic experiment was conducted using four N sources, including urea (U), nitrate-N (N), ammonium-N (AN), and a mixed ammonium-nitrate source (NN), which were applied at two concentrations (2.9 and 5.8 mM L⁻¹). We evaluated Cd accumulation, mineral element uptake, and translocation in rice seedlings under Cd stress. The results indicated that both the form and level of nitrogen markedly affected Cd accumulation. The AN treatment exhibited a strong Cd-reduction effect, especially at the higher nitrogen level, where it significantly reduced Cd concentration in roots and shoots by 68.75% and 26.81%, respectively. In contrast, the N treatment increased Cd accumulation in roots. Nitrogen fertilization also differentially influenced the accumulation of mineral elements, resulting in notable alterations in root Ca, Mg, Cu, and Zn concentrations, while shoot mineral concentrations remained relatively stable. Correlation and random forest analyses revealed a highly significant positive correlation between root Cd concentration and Mg and Cu concentrations, a significant negative correlation with Zn concentration, and a synergistic relationship between the translocation of Cd and that of Ca, Mg, and Cu. Analysis of ion channel tolerance rates further indicated that the AN treatment suppressed Cd uptake by reducing the permeability of root trace element channels to Cd. These findings demonstrate that nitrogen forms modulate Cd accumulation and partitioning by regulating competitive ion uptake and coordinated translocation. In particular, the AN treatment shows promising potential for reducing Cd accumulation while maintaining mineral nutrient balance, thereby providing a theoretical foundation for precise nitrogen management in Cd-contaminated paddy fields. Full article

Nitrogen (N) is an essential nutrient for the growth and development of rice. However, excessive N fertiliser application and low N Use Efficiency (NUE) have led to serious environmental problems and threatened agricultural sustainability. In this study, we compared the physiological and transcriptomic profiles of roots of two cultivars exposed to normal nitrogen (NN) and low nitrogen (LN). The results showed that the LN treatment suppressed root growth and severely affected enzymatic activities in the roots of both rice cultivars compared to the NN treatment. Moreover, HJ753 exhibited significantly higher activities of NITRATE REDUCTASE (NR) and GLUTAMINE SYNTHETASE (GS) in its roots than DJ8 under both LN and NN conditions. Transcriptomic analysis identified 23,205 genes across all samples, with more than 5000 differentially expressed genes (DEGs) detected in response to LN stress in both cultivars. The KEGG analysis revealed that the DEGs were primarily involved in DNA replication, tryptophan metabolism, phenylpropanoid biosynthesis, plant hormone signal transduction, and N metabolism. Under LN stress, most genes associated with tryptophan metabolism and phenylpropanoid biosynthesis pathways remained stable or were upregulated in both cultivars. In contrast, genes related to auxin signalling transduction, N metabolism, and N utilisation exhibited significant genotype-specific expression patterns between HJ753 and DJ8. In conclusion, this study elucidated the genotypic differences in root development and N response mechanisms under LN stress at the molecular level, providing new insights into the regulatory mechanisms of N efficiency that may be used to develop and support the breeding of N-efficient rice cultivars. Full article

Nitrate in groundwater (GW) poses a public-health concern in semi-urban northeastern Saudi Arabia, where households rely on untreated wells. We measured nitrate in 45 wells spanning treated/untreated commercial stations, private domestic wells, and agricultural wells, and linked contamination severity to age-specific risks using the Nitrate Pollution Index (NPI), Chronic Daily Intake (CDI), and Hazard Quotient (HQ). Nitrate ranged from 12 to 380 mg·L⁻¹ (35% > 50 mg·L⁻¹ World Health Organization (WHO) guideline), with untreated private and agricultural wells most affected. Based on NPI, 65% of wells were “clean”, while 18% showed significant to very significant pollution. Infants and children had the highest exposure: CDI frequently exceeded the oral reference dose (1.6 mg·kg⁻¹·d⁻¹), and HQ > 1 occurred in 56% (infants) and 51% (children) of samples from untreated sources. Treated stations consistently achieved lower nitrate and HQ < 1. Sensitivity analysis identified nitrate concentration as the dominant risk driver, followed by ingestion rate, with body weight mitigating the dose. The findings suggest that monitoring based solely on compliance may underestimate risks in sensitive age groups, thereby advocating for immediate actions such as fertilizer management, septic system upgrades, extension of treatment to vulnerable households, and community monitoring. The integrated NPI–CDI–HQ framework provides a replicable methodology for associating groundwater contamination with demographic-specific health risks in arid, water-stressed regions. Full article

Subtropical climate in Florida offers a unique opportunity for sustainable biofuel production using native microalgae cultivated in untreated wastewater. This study bioprospected oleaginous microalgal consortia from a wastewater holding tank at the Thomas P. Smith Water Reclamation Facility in Tallahassee, Florida, aiming to identify strains capable of both nutrient remediation and lipid accumulation. Using Fluorescence-Activated Cell Sorting (FACS), chlorophyll-containing cells were isolated and cultured on BG-11 media. Shotgun metagenomics revealed that the most robust consortia—labeled C3, C4, and C9—were dominated by Chlamydomonas, Acutodesmus, and Volvox spp., alongside diverse bacterial, fungal, and archaeal communities. Functional gene analysis indicated active pathways for photosynthesis, lipid biosynthesis, and nutrient assimilation. In microcosm experiments, these consortia achieved up to 100% ammonia, 95% phosphorus, and 89% nitrate removal, outperforming control treatments. Lipid screening confirmed significant accumulation, with consortium C9 showing the highest yield. These findings underscore the potential of native microalgal consortia for integrated wastewater treatment and biofuel production, advancing circular bioeconomy strategies for subtropical regions. Full article

The mobilization of complex microbial communities from natural resources can be a valuable alternative to the use of single-species biofertilizers when it comes to the decomposition of plant residues. However, the functioning and interaction of microorganisms within these communities remain largely unexplored. Our task was to investigate the cellulose-degrading community using the biofertilizer BAGS (peat-based compost with straw) as an example and define its active component. For this, we monitored the succession of the biofertilizer’s taxonomic composition during two consecutive rounds of its six-month composting process, varying in the applied mineral fertilization. The amount of added nitrogen significantly affected the performance of the biofertilizer, contributing to its high cellulolytic activity. Based on the network analysis, the biofertilizer’s mature phase was determined, and its characteristic ASVs (amplicon sequence variants) were described. Metagenomic analysis of this phase revealed MAGs (metagenome-assembled genomes) corresponding to these ASVs, which contained genes for cellulose and aromatics degradation, as well as genes for nitrogen and sulfur pathways, including anaerobic nitrate reduction and thiosulfate oxidation. Thus, we propose that the cellulose-decomposing bacterial component of BAGS, associated with the mature phase, occupied different trophic niches, not limited to cellulose degradation, which should be considered when designing natural or artificial microbial systems for the decomposition of plant residues. Full article

Nitrate pollution poses a pervasive environmental issue for groundwater systems worldwide, which is particularly pronounced in the agricultural heartlands of the North China Plain. Combining hydrochemical analysis, the Self-Organizing Map algorithm, and Human Health Risk Assessment, 91 shallow groundwater samples were collected to identify the hydrochemical characteristic and the genetic mechanisms of high NO₃⁻ concentration groundwater. The SOM analysis identified three distinct hydrochemical clusters. Cluster 1, with the hydrochemical characteristic of HCO₃-Ca and HCO₃-Mg, is severely contaminated, showing the highest NO₃⁻, Ca²⁺, and TDS. In contrast, the majority of samples fell into Cluster 3, which is characterized by the lowest ion concentrations and an HCO₃-Ca type. Cluster 2, characterized by HCO₃-Ca/Mg, exhibits an intermediate chemical signature with elevated Na⁺, Mg²⁺, and HCO₃⁻. Nitrate concentrations varied widely, with 30.43% of collected samples exceeding the anthropogenic pollution threshold. Agricultural activities are identified as the primary nitrate source, with domestic sewage as a secondary contributor. The Human Health Risk Assessment further reveals that long-term exposure poses non-carcinogenic health risks, particularly for children, who are found to be the most vulnerable group. This study provides a hydrogeochemical perspective on nitrogen pollution in shallow groundwater and offers scientific support for sustainable groundwater management in typical agricultural regions worldwide. Full article

Background/Objectives: Dietary inorganic nitrate (NO₃⁻), primarily sourced from vegetables such as beetroot, has been shown to enhance nitric oxide (NO) bioavailability, with emerging evidence suggesting its potential to modulate autonomic function. However, the effects of NO₃⁻ supplementation on cardiac autonomic recovery post-exercise in hypertensive postmenopausal women remain poorly understood. Using data from a previously conducted randomised controlled trial, this study investigated the effects of acute (800 mg) and seven-day (400 mg/day) beetroot juice NO₃⁻ supplementation on ultra-short-term post-exercise cardiac parasympathetic recovery in hypertensive older women. Methods: In a triple-blind, placebo-controlled crossover design, fourteen postmenopausal women (59 ± 4 y) with hypertension completed two intervention arms (NO₃⁻ and placebo). Ultra-short-term heart rate variability (HRV) indices (SDNN, RMSSD, HF) were assessed across 5 min post-exercise recovery using 60 s windows. Plasma NO₂⁻ and NO₃⁻ concentrations were measured via chemiluminescence. Results: Both acute and seven-day NO₃⁻ supplementation significantly increased plasma NO₂⁻ and NO₃⁻ concentrations compared to placebo (p < 0.001). Cardiac vagal recovery, assessed via SDNN and RMSSD, was significantly enhanced in both conditions, with greater and more sustained improvements observed after the seven-day protocol. HF power was significantly higher, but only after seven-day supplementation (p = 0.009). Conclusions: Inorganic NO₃⁻ supplementation enhances post-exercise cardiac parasympathetic reactivation in hypertensive postmenopausal women. Notably, the seven-day intake (400 mg/day) protocol elicited superior autonomic benefits compared to an acute high dose. These findings highlight the potential of NO₃⁻ as a non-pharmacological strategy for improving cardiovascular autonomic recovery in high-risk populations. Full article

Microplastics (MPs) pollution assessment must not pollute. Inspired by this catch phrase, we critically evaluated the environmental impact, safety, and effectiveness of various analytical strategies currently used to assess MPs contamination on sand. Density separation enables the isolation of MPs from sand. We highlighted the major drawbacks of using the standard high-density solutions. As we recognized there is room for greenness improvement in this hot research field, we considered 21 reagents able to provide high-density media. We aimed to put forward the green MPs determination protocol to be used in subsequent expert citizen science national campaign. The analytical workflow was optimized studying MPs contamination of composite sand specimens representatively sampled from a large beach-dune complex WWF oasis exposed to the effect of tourism in Venice (Italy). MPs have been quantified and characterized. We suggest calcium nitrate as the best trade-off reagent providing both greenness/safety and efficacy. Calcium nitrate can be upcycled from industrial waste streams according to the circular economy vision. Additionally, we critically reviewed all other critical steps of the MPs isolation to put forward a preeminent green, simple, reliable, and logical approach to the analysis of MPs in sand for expert citizen science campaigns. Full article

This study examined the sediment microbial communities at 12 stations within the Meretrix meretrix farming area in Rudong, Jiangsu Province, utilising high-throughput sequencing. It elucidates the ecological relationships between the sediment microbial communities and the primary physical and chemical factors influencing the farming water and sediment. The results indicated that the microbial communities comprised 55 phyla. The Shannon index ranged from a minimum of 8.97 to a maximum of 9.96, while the Simpson index varied from 0.996 to 0.997, indicating a uniform species distribution. β diversity analysis revealed significant spatial diversity among the communities. Dominant bacterial groups included Proteobacteria (25.2–38%) and Desulfobacterota (10.4–14.4%), with Desulfobacterota reaching a peak of 14.4% at tidal creek station S2, reflecting the sulphate reduction process associated with organic pollution input. At the genus level, Woesia (9.15–17.16%), Desulfobacterota, and Subgroup_22 were identified as core functional bacteria. Redundancy analysis indicated that phosphate and nitrate were the primary drivers of community variation, accounting for a cumulative interpretation rate of 43.2%. Spearman correlation analysis confirmed that fine-grained sediments were more likely to store organic matter, significantly promoting the colonisation of AQS1 (p < 0.05) and Cohaesibacter (p < 0.05), while inhibiting Puniceispirillales (p < 0.01). An alkaline environment positively selects for sulphur-cycling bacteria, such as Desulfatiglans (p < 0.05). This study provides technical support for the regulation of sediment environments and the promotion of healthy clam culture practices. Full article

The hydrological processes of red soil slope farmland are complex, and the vertical migration of nitrogen (N) is influenced by these processes, which present different layering characteristics of water flow. Previous studies on the vertically stratified transport of N on slope soils have mainly relied on rainfall simulation, lacking a comprehensive study of the overall process of N leaching from surface soil to underground under natural conditions. To investigate the impact of these hydrological processes on the transport of N at different layers under natural rainfall events, large-scale field runoff plots were constructed as draining lysimeters to conduct a consecutive 2-year observation experiment at Jiangxi Soil and Water Conservation Ecological Science and Technology Experimental Station, China. The runoff (the water of 0 cm), interflow, deep percolation, soil moisture content (SMC), total nitrogen (TN), nitrate nitrogen (NO₃⁻-N) and ammonium nitrogen (NH₄⁺-N) concentrations were monitored and determined. The N loss of red soil farmland under two treatments, namely grass mulching (FC, a coverage of 100% with Bahia grass) and exposed treatment (BL, without anything covered), were measured. The relationships between hydrological factors and different forms of N losses were analyzed. The results indicate the following: (1) Deep percolation is the main pathway of water loss and N loss for red soil slope farmland, accounting for over 85% of the total water loss and N Loss. Grass mulching can significantly reduce surface runoff and N loss. (2) Vertically stratified N is mainly NO₃⁻-N, and the concentrations of each form of N show the same trend: deep percolation > interflow > runoff. (3) Water loss, rainfall, and SMC are closely related to the stratified loss of N, with correlation coefficients ranging from 0.74 to 0.98. The correlation analysis and redundancy analysis (RDA) on the relationships between different forms of N losses and hydrological factors indicate that rainfall was the primary factor driving the stratified loss of N in red soil slope farmland. 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

Rice blast, caused by Magnaporthe oryzae, is one of the most devastating diseases threatening global rice production. Although host resistance represents a sustainable control strategy, the underlying mechanisms mediated by the rhizosphere microbiome remain poorly understood. In this study, we selected four rice varieties with varying resistance to blast and demonstrated, through an integrated approach of 16S rRNA/ITS amplicon sequencing, untargeted metabolomics, and soil physicochemical analysis, that the rice genotype reprograms the genotype-root exudate-rhizosphere microbiome system. Results showed that the resistant variety P104 significantly decreased the soil pH while increasing the contents of total nitrogen, ammonium nitrogen, and nitrate nitrogen. On the other hand, the susceptible variety P302 exhibited higher pH and available phosphorus content. Furthermore, the rhizosphere of P104 was enriched with specific beneficial microbes such as Desulfobacterota, Ascomycota, and Pseudeurotium, and activated defense-related metabolic pathways including cysteine and methionine metabolism and phenylpropanoid biosynthesis. In contrast, susceptible varieties showed reduced bacterial diversity and fostered a microecological environment more conducive to pathogen proliferation. Our findings indicate that blast-resistant rice genotypes are associated with a protective rhizosphere microbiome, potentially mediated by alterations in root metabolism, thereby suppressing pathogen establishment. These insights elucidate the underground mechanisms of blast resistance and highlight the potential of microbiome-assisted breeding for sustainable crop protection. Full article

The structure and function of alpine steppes are maintained largely by dominant species, which in turn determine the productivity and stability of plant communities. Nutrient acquisition and stress regulation may, to some extent, be mediated by phyllospheric microbiota at the interface of plants with the atmosphere, and phyllospheric microbes are capable of amplifying and transmitting vegetation responses to degradation. Previous research has mainly addressed climate, soil, vegetation and soil microbiota or has assessed phyllosphere communities as a whole, thereby overlooking the specific responses of phyllospheric bacteria associated with the vegetation-dominant species Stipa purpurea along gradients of vegetation degradation in alpine steppes. In this study, we characterised vegetation degradation at the community level (from non-degraded to severely degraded grasslands) and quantified associated changes in the dominant species Stipa purpurea (cover, height and aboveground biomass) and its phyllospheric bacterial communities, in order to elucidate response patterns within the coupled system of host plants, phyllosphere microbiota, climate (mean annual temperature and precipitation) and soil physicochemical properties. Compared with non-degraded (ND) grasslands, degraded sites had a 22.6% lower mean annual temperature (MAT) and reductions in total nitrogen, nitrate nitrogen, organic matter (OM) and soil quality index (SQI) of 49.4%, 55.6%, 46.8% and 47.6%, respectively. Plant community cover and the aboveground biomass of dominant species declined significantly with increasing degradation. Along the vegetation-degradation gradient from non-degraded to severely degraded alpine steppes, microbial source-tracking analysis of the phyllosphere of the dominant species Stipa purpurea revealed a sharp decline in the contribution of phyllospheric bacterial sources. Estimated contributions from non-degraded sites to lightly, moderately and severely degraded sites were 95.68%, 62.21% and 6.89%, respectively, whereas contributions from lightly to moderately degraded and from moderately to severely degraded sites were 34.89% and 16.47%, respectively. Bacterial richness increased significantly, and β diversity diverged under severe degradation (PERMANOVA, F = 5.48, p < 0.01). From light to moderate degradation, biomass and relative cover of the dominant species decreased significantly, while the phyllosphere bacterial community appeared more strongly influenced by the host than by environmental deterioration; the community microbial turnover index (CMTB) and microbial resistance potential increased slightly but non-significantly (p > 0.05). Under severe degradation, worsening soil conditions and hydrothermal regimes exerted a stronger influence than the host, and CMTB and microbial resistance potential decreased by 6.5% and 34.1%, respectively (p < 0.05). Random-forest analysis indicated that climate, soil, phyllosphere diversity and microbial resistance jointly accounted for 42.1% of the variation in constructive-species biomass (R² = 0.42, p < 0.01), with the remaining variation likely driven by unmeasured biotic and abiotic factors. Soil contributed the most (21.73%), followed by phyllosphere diversity (9.87%) and climate (8.62%), whereas microbial resistance had a minor effect (1.86%). Specifically, soil organic matter (OM) was positively correlated with biomass, whereas richness, beta diversity and MAT were negatively correlated (p < 0.05). Taken together, our results suggest that under ongoing warming on the Qinghai–Tibet Plateau, management of alpine steppes should prioritise grasslands in the early stages of degradation. In these systems, higher soil organic matter is associated with greater phyllospheric microbial resistance potential and increased biomass of Stipa purpurea, which may help stabilise this dominant species and slow further vegetation degradation. Full article