Search Results (480)

Nitrogen (N) fertilization is a fundamental agronomic practice that governs crop productivity, yet its effects on the molecular composition and chemical stability of soil organic carbon (SOC) remain poorly understood, especially in cereal–legume intercropping systems. Traditional studies have focused on total SOC stocks rather than molecular-level changes, and the mechanistic pathway linking N addition to SOC functional group transformation remains unclear. This study addressed these critical gaps by investigating how graded N addition (0, 180, 270, and 360 kg N ha⁻¹) reshapes SOC chemistry in a subtropical soybean–maize intercropping system. Soil physicochemical properties, inorganic N pools, N-transformation enzyme activities (urease, nitrate reductase, and glutaminase), microbial biomass indices, labile organic carbon fractions (particulate, mineral-associated, and dissolved organic carbon), and SOC functional groups characterized by Fourier transform infrared (FTIR) spectroscopy were quantified across a two-year field experiment (2024–2025). Results showed that increasing N rates significantly elevated nitrate nitrogen (NO₃⁻-N) accumulation while depressing soil pH. Nitrogen-transformation enzymes, especially nitrate reductase and glutaminase, responded strongly and positively to the N gradient. Microbial biomass carbon (MBC) and nitrogen (MBN) increased with moderate N input but exhibited saturation or decline at 360 kg N ha⁻¹, accompanied by reduced microbial carbon use efficiency (CUE) and a lower MBC/MBN ratio. Among labile carbon fractions, dissolved organic carbon (DOC) was the most responsive pool, increasing markedly with N addition and correlating strongly with NO₃⁻-N. FTIR analysis revealed that N addition shifted SOC functional group composition toward chemically recalcitrant structures: the relative abundances of aromatic C=C and carbonyl C=O groups increased significantly, whereas labile C–O groups declined. Random forest modelling identified C=C, NO₃⁻-N, and DOC as the three most influential predictors of SOC chemical composition. Structural equation modelling (SEM) demonstrated a sequential mechanistic pathway: N fertilization increased NO₃⁻-N, which stimulated glutaminase activity and enhanced DOC, ultimately promoting C=C/C=O stabilization and explaining 91.3% of the variance in SOC aromaticity. These findings reveal that N addition does not merely augment SOC quantity but fundamentally transforms its molecular architecture toward greater chemical stability through a nitrate-mediated, enzyme–labile carbon coupling mechanism. This study provides a novel spectroscopic–mechanistic framework for understanding carbon–nitrogen interactions in intercropping agroecosystems and informs precision N management strategies aimed at simultaneous crop production and long-term soil carbon sequestration. Full article

Choline-based ionic liquids (ILs) have emerged as promising candidates for application in multifaceted avenues, including electrochemistry, biomaterials, and environmental remediation technologies. However, their regulatory effects on the growth of agricultural plants have rarely been discussed. In this study, 14 choline–fatty acid ILs ([Chl][FA] ILs) containing different FA anions were synthesized, and their effects on the maize growth were investigated. Hydroponic experiments revealed that low concentrations (20 mg/L) of dicarboxylic acid-based [Chl][FA] ILs (e.g., choline pentane diacid [Chl][Pent]) significantly promoted maize root and shoot biomass, whereas higher concentrations inhibited it. Specifically, [Chl][Pent] enhanced chlorophyll content without altering Fv/F₀, upregulated nitrate reductase (NR) and glutamine synthetase (GS) activities, and stimulated the expression of key nitrogen metabolism (NR and GS) and photosynthetic (Rubisco) genes. Pathway analyses of differentially expressed genes indicated that [Chl][Pent] was associated with the upregulation of nitrogen and glycerophospholipid metabolism. [Chl][Pent] increased the average grain yield by 6.88% over two years compared to CK. Field application of [Chl][Pent] increased grain yield and protein accumulation relative to both control and choline chloride treatments. Overall, these findings demonstrate the potential of dicarboxylic acid-based [Chl][FA] ionic liquids as eco-friendly biostimulants for enhancing crop growth, yield, and quality. Full article

In Northeast China’s black soil region, we examined how different straw return strategies—no return (CK), direct straw incorporation (SD), and biochar application (BC)—interact with three nitrogen levels (N0, N60, N100) to affect soil properties, enzyme activities, and the chitin-degrading ChiA functional gene. Both SD and BC significantly increased soil nutrients (total carbon, ammonium nitrogen, available potassium, and soil organic matter) and reduced bulk density. They also enhanced the activities of key carbon—and nitrogen-cycling enzymes, including nitrate reductase and N-acetylglucosaminidase. Straw return method and nitrogen rate both influenced ChiA abundance, but straw management was the primary driver of ChiA community structure according to principal component analysis. Actinobacteria and Proteobacteria dominated the bacterial phyla. Correlation analysis identified bulk density, total nitrogen, C/N ratio, available potassium, soil organic matter, and NAG activity as key factors shaping the ChiA community. Both straw return strategies improved soil fertility and chitin degradation potential. Among them, direct straw return combined with conventional nitrogen application (SD N100) showed the most balanced performance in sustaining soil health and agricultural productivity in the Mollisol region. Full article

Continuous cropping and long-term excessively using nitrogen fertilizers in facilities vegetables has led to the imbalance of nitrogen conversion in soil and plants. A pot experiment was conducted to investigate the effects of biochar on soil and plant nitrogen transformation in cucumber under simulated different nitrogen contents in facility cultivation. Eight pot treatments: no nitrogen (N0), 100 kg·hm⁻² of nitrogen (N100), 150 kg·hm⁻² of nitrogen (N150), 200 kg·hm⁻² of nitrogen (N200), and which with the addition of 5% biochar named BN0, BN100, BN150, BN200. The results showed that BN100 (100 kg·hm⁻² N + 5% biochar) significantly increased the soil nitrogen transformation and the growth of cucumber. Specifically, the nitrate reductase, GOGAT activity, and the nitrate nitrogen absorption of cucumber roots were enhanced. It also elevated soil pH by 0.43 units and increased urease, neutral protease, nitrite reductase (NIR, and NR activities by 136.63%, 23.95%, 18.4%, and 12.1%, respectively. The relative abundance of nitrogen metabolism-related microorganisms such as Nitrospira and Sphingomonas were increased. The nitrification, nitrogen fixation, the contents of nitrate nitrogen and nitrite nitrogen in soil were increased. These changes collectively improved soil nitrogen transformation and ultimately promoted cucumber plant growth. This study reveals the potential role of biochar in regulating soil nitrogen transformation and facilitating plant growth. Full article

Wildfires severely disrupt soil nitrogen (N) cycling, yet the mechanisms driving this disruption in fragile karst forest ecosystems remain poorly understood. We investigated how wildfires affect soil N transformation dynamics and the microclimatic drivers of these dynamics in a karst forest. Using an in situ paired burned versus unburned plot design, we evaluated post-fire soil physicochemical properties, N fractions, and N-acquiring enzyme activities in the 0–10 cm soil layer. Wildfires significantly deteriorated the soil microenvironment, increasing mean soil temperature by 9.93% and bulk density by 36.66%, while sharply reducing soil water content, porosity, and saturated hydraulic conductivity. Consequently, the fires severely depleted total and organic soil N pools. Furthermore, N-acquiring enzymes (urease, protease, nitrate reductase, and nitrite reductase) initially declined in activity before gradually recovering. Notably, partial least squares structural equation modeling (PLS-SEM) revealed a fundamental shift in the drivers of nitrogen transformation. In unburned soil, abiotic climatic factors regulated N dynamics. After wildfire, enzyme-mediated biological processes controlled N dynamics, and these processes were constrained by altered soil physics. Restoring soil physical structure and stimulating enzymatic mineralization are therefore critical, rate-limiting steps for the recovery of soil N reservoirs in fire-prone karst landscapes. Full article

Hydrogen sulfide (H₂S) functions as a pivotal gaseous signaling molecule in plants, yet its role in promoting crop yield remains elusive. Here, we demonstrate that sodium hydrosulfide (NaHS) application, a donor of hydrogen sulfide (H₂S), significantly accelerates growth, promotes flowering, and enhances grain yield in rice (Oryza sativa L.). Optimal NaHS treatment increased plant height, root length, and biomass accumulation, concomitant with elevated sucrose, starch, chlorophyll contents, and nitrate reductase activity. Integrated transcriptomic and proteomic analyses revealed that NaHS reprograms key biological pathways, including photosynthesis, carbon metabolism, lipid metabolism, the hormone signal transduction pathway, and reactive oxygen species (ROS) homeostasis. NaHS also remodels fatty acid metabolism, significantly increasing unsaturated fatty acids, linoleic acid (C18:2n6c), and α-linolenic acid (C18:3n3)—the latter serving as the direct precursor for JA biosynthesis—thereby fueling jasmonic acid (JA) biosynthesis. NaHS treatment also induced ROS accumulation while simultaneously activating antioxidant enzymes, maintaining redox homeostasis, and promoting cell proliferation in root meristems. Transmission electron microscopy revealed that NaHS enlarges peroxisomes and increases chloroplast oil body number, linking organellar dynamics to enhanced JA synthesis and ROS signaling. Collectively, our findings establish NaHS as a novel chemical regulator that coordinates JA and ROS signaling to boost rice growth, flowering, and grain yield, offering a promising strategy to improve crop productivity. Full article

Understanding how external nitrogen sources regulate nitrogen fate in river water is critical for improving nitrogen removal and reducing greenhouse-gas risk. Here, short-term microcosm incubations were conducted using source water as the background matrix and seven representative source inputs. By integrating hydrochemical analyses, bacterial community profiling, metagenomics, RT-qPCR, and process-rate measurements, we evaluated source-dependent shifts in nitrogen-cycling pathways. Manure-related inputs generated the highest organic and nitrogen loading, suppressed nitrification, enhanced nrfA (cytochrome c nitrite reductase) abundance and transcription, and promoted DNRA, indicating a shift toward nitrogen retention via ammonium regeneration. In contrast, sewage-related inputs maintained relatively high NO₃⁻ availability, elevated nirS (cytochrome cd1 nitrite reductase) and nosZ (nitrous oxide reductase) expression, and enhanced denitrification, but also increased N₂O production. Metagenomic, transcriptional, and rate-based evidence consistently identified 12 h as a critical window for source-dependent pathway redistribution, highlighting the importance of short-term monitoring for detecting rapid nitrogen-cycle responses following pollution inputs. These findings support source-oriented nitrogen management that considers both nitrogen loading and hydrochemical controls on nitrate fate. Full article

The toxicity of copper (Cu) severely affects the growth and physiological metabolism of plants. 2-(3,4-Dichlorophenoxy) triethylamine (DCPTA) is a plant growth regulator known to enhance plant tolerance to various abiotic stresses; however, its specific role in mitigating Cu toxicity via cell wall modulation and nitrogen metabolism remains unclear. “Zhongnong 26” (Cucumis sativus L.) seedlings were subjected to a randomized block design with four treatments: control (CK), 0.25 mg/L DCPTA, 50 μM Cu, and 50 μM Cu + 0.25 mg/L DCPTA, with three biological replicates per treatment. The results indicated that DCPTA application significantly alleviated Cu-induced growth inhibition. Specifically, DCPTA improved root system architecture by markedly increasing total root length (68.8%), surface area (68.7%), and the number and length of secondary lateral roots (69.6%, 173.2%). Furthermore, DCPTA enhanced the biosynthesis of cell wall polysaccharides—including pectin (24.3%), hemicellulose 1 (22.4%), hemicellulose 2 (23.7%) and cellulose (33.1%) in roots. Fourier Transform Infrared (FTIR) spectroscopy analysis revealed that DCPTA modified functional groups (e.g., –OH, –COOH) within the cell wall, enhancing their metal-chelating capacity. Consequently, DCPTA promoted the immobilization of Cu in the root cell wall fractions (particularly pectin and HC2) and shifted Cu into less toxic, pectate- and protein-bound forms, thereby reducing its translocation to leaves. Additionally, DCPTA restored the activities of key nitrogen metabolism enzymes in leaves and roots. Compared with Cu treatment alone, nitrate reductase (NR) activity increased by 77.7% and 90.6%, while glutamine synthetase (GS) activity remained stable, and glutamate synthase (GOGAT) activity increased by 10.3% and 71.3% in leaves and roots, respectively. In conclusion, DCPTA enhances copper sequestration in roots by coordinating the regulation of root structure and cell wall strengthening (with an increase in pectin and hemicellulose content). This is crucial for protecting the nitrogen metabolism within the cells (including the enzymes that drive the nitrate–ammonium reduction pathway) to maintain metabolic balance under Cu stress. Full article

Nitrate (NO₃⁻) serves as a critical nitrogen source and signaling molecule essential for its growth and quality formation. Although substantial genetic variation in nitrogen use efficiency (NUE) has been documented among tea cultivars, a systematic characterization of nitrate (NO₃⁻) absorption kinetics and the associated genome-wide transcriptional regulatory networks across varying nitrate concentrations remains lacking. This study employed ¹⁵N isotope labeling and transcriptome sequencing to systematically analyze the absorption characteristics and molecular response mechanisms of the cultivars ‘Longjing 43’ and ‘Zhongming 6 hao’ under varying NO₃⁻ concentrations. Results revealed significant differentiation in absorption strategies: ‘Zhongming 6 hao’ exhibited a significantly higher absorption rate at low concentrations, whereas ‘Longjing 43’ demonstrated enhanced performance at high concentrations. Transcriptome analysis indicated that both cultivars shared coordinated regulation of ‘photosynthesis’ and ‘nitrogen metabolism’ pathways. Furthermore, 14 nitrogen metabolism genes and 64 differentially expressed transcription factors (including MYB, NAC, and LBD families) were identified. Specifically, the CsNiR gene (encoding nitrite reductase) was functionally validated; silencing of CsNiR significantly reduced nitrite reductase activity, confirming its positive regulatory role. This study provided a theoretical framework and key candidate genes for breeding nitrogen-use-efficient varieties, which is essential for sustainable tea production. Full article

Light availability is a key environmental factor regulating nitrogen assimilation, carbon metabolism, and nutritional quality in leafy vegetables grown in controlled environments. However, how practical lighting regimes used in plant factories with artificial lighting (PFALs) influence the coordination between nitrogen assimilation and central carbon metabolism across different lettuce cultivar types remains insufficiently understood. This study investigated how moderate differences in photosynthetic photon flux density (PPFD) influence nitrogen metabolism and metabolic coordination in hydroponically cultivated lettuce. Two cultivars representing contrasting morphological types, iceberg lettuce (‘Celebration’) and leaf lettuce (‘Sunny’), were grown under LED light intensities of 150 and 200 µmol·m⁻²·s⁻¹. Nitrate, nitrite, and ammonium concentrations were measured together with the activities of nitrate reductase (NRA) and nitrite reductase (NiRA), as well as ascorbic acid content. Metabolomic profiling was additionally performed to characterize broader metabolic responses. Higher light intensity enhanced nitrate reduction capacity in both cultivars, but the resulting patterns of nitrogen accumulation were strongly genotype-dependent. The leaf lettuce cultivar ‘Sunny’ exhibited increased NRA and reduced nitrate accumulation under higher light intensity, whereas the iceberg lettuce cultivar ‘Celebration’ accumulated more nitrate under the same conditions. Ammonium responses further suggested differences in downstream nitrogen assimilation processes. Elevated light intensity also increased ascorbic acid levels in both cultivars. Metabolomic analysis revealed contrasting cultivar-specific shifts in central carbon metabolism, particularly involving soluble sugars and tricarboxylic acid cycle intermediates, indicating differential coordination between carbon metabolism and nitrogen utilization. Overall, these findings demonstrate that moderate changes in light intensity within the practical PFAL cultivation range can significantly influence the integration of carbon and nitrogen metabolism in lettuce. Importantly, cultivar-specific physiological traits determine how these metabolic responses translate into nitrate accumulation and nutritional quality in controlled-environment production systems. Full article

Excessive nitrate accumulation in leafy vegetables presents significant health risks, requiring sustainable strategies to optimize yield while minimizing nitrogen-related anti-nutritional factors in controlled environments. This study investigated the effects of varying LED light intensities 236.9 µmol·m⁻²·s⁻¹ (high), 189.8 µmol·m⁻²·s⁻¹ (medium), and 117.6 µmol·m⁻²·s⁻¹ (low) on nitrates (NO₃⁻) dynamics, growth, and biochemical composition in two Lollo Rossa lettuce cultivars, Carmesi and Carnelian, grown in NFT hydroponic systems. Conducted under constant temperature (20/18 °C day/night) and CO₂ (625 µmol·mol⁻¹) to isolate light’s influence, the experiment used a replicated design with three replicates per treatment, each including two cultivars. Morphological traits (plant height, rosette diameter, leaf number, biomass, root development) and biochemical parameters (nitrate and sugar contents) were assessed via mean comparisons, trends, and correlations. Results demonstrated that higher light intensity significantly suppressed nitrate accumulation in lettuce through enhanced assimilation and dilution effects linked to increased growth. Nitrate levels dropped to 2091.67 mg kg⁻¹ from 2443.33 mg kg⁻¹ in Carmesi and 2013.33 mg kg⁻¹ from 2515.00 mg kg⁻¹ in Carnelian. Negative correlations were observed between nitrate content and growth parameters: nitrates vs. fresh biomass (r = −0.89); nitrates vs. plant height (r = −0.79). Concurrently, it boosted carbohydrate content (Carmesi: 3.03 °Brix; Carnelian: 3.08 °Brix) and promoted vigorous growth, with Carmesi achieving superior metrics under high light (height: 22.12 cm, rosette diameter: 29.87 cm, fresh biomass: 206.88 g, root biomass: 19.58 g) compared to low light (17.45 cm height, 183.42 g biomass). Carnelian exhibited similar trends but prioritized root elongation. These findings underscore light’s role in regulating nitrate transporters and assimilation enzymes (e.g., nitrate reductase), offering a low-cost approach to reduce nitrate risks, enhance nutritional quality, and improve yield in controlled horticultural systems (CHS). 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

This study focused on alfalfa (Medicago sativa cv. Xinmu No. 4) as the experimental material, and a two-year field plot controlled experiment was conducted to compare the effects of different co-application ratios of organic and chemical fertilizers on alfalfa yield, soil nutrient status, and soil biological characteristics. The six fertilization treatments were as follows: CM0 (100% cattle manure), CM1 (75% cattle manure + 25% chemical fertilizer), CM2 (50% cattle manure + 50% chemical fertilizer), CM3 (25% cattle manure + 75% chemical fertilizer), CM4 (100% chemical fertilizer), and CK (no fertilizer application). The results showed that alfalfa hay yield was highest under the CM3 treatment in both 2024 and 2025, representing increases of 38.03% and 40.85%, respectively, compared with the control (CK). Relative to the other treatments, CM3 significantly increased soil total nitrogen, alkali-hydrolyzable nitrogen, available phosphorus, readily available potassium, and organic matter contents. In addition, CM3 markedly enhanced the activities of soil nitrate reductase (NR), nitrite reductase (NiR), and the root enzymes glutamate synthase (GOGAT) and glutamine synthase (GS). The combined application of organic and chemical fertilizers significantly reshaped the soil bacterial community structure associated with alfalfa. Under the CM3 treatment, Chao1, Shannon, and ACE indices of soil bacterial diversity increased, whereas the Simpson index decreased. Moreover, the CM3 treatment was associated with higher relative abundances of several key bacterial phyla and genera. The 25% cattle manure plus 75% chemical fertilizer (CM3) treatment exhibited the strongest overall effects, significantly increasing total alfalfa hay yield, enhancing soil macronutrient availability and key enzyme activities, improving soil microbial α-diversity, and optimizing soil bacterial community structure. This treatment consistently outperformed the no-fertilizer control (CK) and all other organic–inorganic fertilizer combinations. Collectively, these findings provide robust scientific evidence supporting strategies to increase forage productivity, mitigate environmental impacts, and promote the sustainable development of the grassland industry. Full article

To address ammonium nitrogen (NH₄⁺-N) and nitrite accumulation in intensive marine shrimp aquaculture, a marine recirculating aquaculture system (RAS) for Penaeus vannamei centered on a moving bed biofilm reactor (MBBR) was constructed to investigate the microbial basis of nitrogen removal. The results showed that the MBBR contributed most to NH₄⁺-N removal, demonstrating favorable nitrification potential under marine conditions (0.513 mg·L⁻¹·h⁻¹). The biofilm carrier formed a complete attached layer and developed a mature biofilm structure. Microbial community analysis revealed clear differentiation between the biofilm and sediment. The biofilm community was dominated by norank_f__Caldilineaceae (9.89%). Linear discriminant analysis effect size identified the nitrifying genus Nitrospira to be significantly enriched on the biofilm side (α = 0.05, linear discriminant analysis > 2.0). In addition, PICRUSt2-based functional prediction suggested a higher potential in biofilm than in sediment for ammonia oxidation and downstream nitrogen transformation, involving ammonia monooxygenase (EC:1.14.99.39), hydroxylamine dehydrogenase (EC:1.7.2.6), nitrate reductase (EC:1.7.99.4), and nitrite reductase (EC:1.7.2.1). Thus, this study provides a microbial basis and process strategy for P. vannamei RAS. Full article

Low-temperature stress adversely impairs rice germination and seedling establishment. This study assessed a nano-bio-priming strategy using lecithin (L) and silicon dioxide nanoparticles (SiO₂ NPs) to enhance chilling tolerance. Two fragrant rice cultivars (Xiangyaxiangzhan and Meixiangzhan 2) were primed with six combinations of lecithin (0, 50, and 100 μmol·L⁻¹, denoted as L0, L1, and L2) and SiO₂ NPs (0 and 100 mg·L⁻¹, denoted as S0 and S1) and exposed to optimal temperature (25 °C) or low-temperature stress (15 °C). Low-temperature stress delayed germination onset by two days. Combined priming treatments L1S1 and L2S1 significantly alleviated this inhibitory effect. Crucially, cultivar-specific responses were evident in Meixiangzhan 2, where L1S1 increased the germination vigor index by 50.97%. Meanwhile, the effect was less pronounced or inhibitory at normal temperature in Xiangyaxiangzhan. Priming substantially enhanced seedling growth, and L2S1 maximally increased root and shoot length in Meixiangzhan 2 by 55.30% and 15.82%, respectively. Furthermore, biomass accumulation was strongly promoted. L1S1 increased total dry weight and total fresh weight in Meixiangzhan 2 by 19.64% and 23.48%, respectively. Physiologically, priming elevated chlorophyll and carotenoid contents upregulated the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and increased levels of soluble protein and ascorbate (AsA), while maintaining nitrate reductase (NR) activity and hydrogen peroxide (H₂O₂) homeostasis. These physiological improvements were positively correlated with enhanced growth. Our findings demonstrate that co-priming with lecithin and SiO₂ NPs is a potent strategy for enhancing low-temperature tolerance, with efficacy depending on both the treatment combination and rice genotype. Full article