Search Results (90)

This study investigated the impact of nitrogen (N) fertilization on the yield and grain filling (GF) characteristics of two conventional japonica rice varieties with distinct panicle types: Yangchan 3501 (large-panicle: spikelets per panicle $> 150$) and Nangeng 46 (medium-panicle: $100 <$ spikelets per panicle $< 150$). Field experiments were conducted over two growing seasons (2022–2023) with three N application rates (T1: 225 kg ha⁻¹, T2: 270 kg ha⁻¹, T3: 315 kg ha⁻¹). Key measurements included tiller dynamics, panicle composition, GF parameters modeled using the Richards equation, and enzyme activities related to nitrogen metabolism (Fd-GOGAT, NR) and carbohydrate transport (α-amylase, SPS). Results showed that the yield increased with higher N levels for both varieties, with Yangchan 3501 achieving higher yields primarily through increased grains per panicle (15.65% rise under T3 vs. T1), while Nangeng 46 relied on panicle number (8.83% increase under T3 vs. T1). Nitrogen application enhanced Fd-GOGAT and NR activities, prolonging photosynthesis and improving GF rates, particularly in the inferior grains of Yangchan 3501 during middle and late stages. However, a high N reduced seed-setting rates and 1000-grain weight, with larger panicle types exhibiting a greater sensitivity to N-induced changes in branch structure and assimilate allocation. This study highlights that optimizing N management can improve nitrogen-metabolism enzyme activity and GF efficiency, especially in large-panicle rice, while medium-panicle types require higher N inputs to maximize panicle number. These findings provide actionable insights for achieving high yields and efficient nutrient use in conventional rice cultivation. Full article

Qingke (Hordeum vulgare L. var. nudum Hook. f.), a staple crop in the Tibetan Plateau, suffers from severe yield reduction under continuous cropping (by 38.67%), yet the underlying mechanisms remain unclear. This study systematically investigated the effects of 23-year continuous cropping (23y-CC) on the nutrient dynamics, carbohydrate metabolism, and enzymatic activities in Qingke leaves across five developmental stages (T1: seedling; T2: tillering; T3: jointing; T4: flowering; T5: filling). Compared to the control (first-year planting), 23y-CC significantly reduced leaf nitrogen (N), phosphorus (P), and potassium (K) contents by 60.94%, 47.96%, and 60.82%, respectively, at early growth stages. Key nitrogen-metabolizing enzymes, including glutamate synthase (GOGAT), glutamine synthase (GS), and nitrate reductase (NR), exhibited reduced activities under 23y-CC, indicating impaired nitrogen assimilation. Carbohydrate profiling revealed lower starch and glucose contents but higher sucrose accumulation in later stages (T4–T5) under 23y-CC, accompanied by the dysregulation of sucrose synthase (SS) and invertase activities. These findings elucidate how continuous cropping disrupts nutrient homeostasis and carbon allocation, ultimately compromising Qingke productivity. This study provides novel insights into agronomic strategies for mitigating continuous cropping obstacles in Qingke. Full article

Fertilization in sustainable agriculture aims to provide optimal nutrients to plants while minimizing negative impacts on the environment and human health. This study aimed to determine the effect of various nitrogen fertilizer doses of 0, 50, 200, and 300 kgN ha⁻¹ on the chemical and biochemical composition of the leaves of nettle (Urtica dioica L.). Nettle leaves were harvested in late April to early May, before flowering. The contents of Zn, Cu, Mn, and Fe, as well as chlorophylls a and b, carotenoids, ascorbic acid, antioxidant, and catalase activity were determined. The result of catalase activity in nettle leaves was used to calculate the resistance index and the actual value of this enzyme activity, which was given as percentage change. Based on the analysis, nitrogen fertilization was found to have a statistically significant effect on the formation of the tested chemical and biochemical parameters in nettle leaves. The highest dose of nitrogen caused a statistically significant increase in the content of Zn, Mn, and assimilation pigments. The content of ascorbic acid ranged from 8.7 to 115 mg 100 g⁻¹ f.m. and, in contrast to the antioxidant and catalase activity, decreased with increasing nitrogen dose. The relative change index (RCh) showed the following effect of nitrogen dose on catalase activity: N300 > N200 > N50. The low value of the plant resistance index (RP) for the nitrogen dose of 300 kg N ha⁻¹ indicates that this dose had the greatest effect (lowest resistance) on catalase activity. Thus, the impact of the stress factor (nitrogen fertilization) was greatest at the highest dose. No statistically significant differences in catalase activity were found between N0 and N50. It was also demonstrated that the contents of Zn and Mn had a statistically significant and positive correlation with chlorophyll a and chlorophyll b. Full article

High nitrogen use efficiency is crucial for enhancing spinach’s tolerance to low nitrogen stress and minimizing nitrate accumulation. Here, we report that SoNRT3, a NAR2 family protein, modulates nitrate uptake and plant growth under low-nitrate conditions. SoNRT3 expression was induced by low nitrate availability in roots and prolonged nitrogen deficiency in shoots. Compared to wild-type Arabidopsis thaliana, lines overexpressing SoNRT3 exhibited higher root fresh weight, activities of nitrogen reduction/assimilation-related enzymes, tap root length, and total root diameter under low-nitrate (0.25 mM) conditions. SoNRT3 silencing reduced taproot length, lateral root number, shoot/root biomass, and ¹⁵${\mathrm{N}\mathrm{O}}_3^{-}$ uptake in spinach grown under low-nitrate conditions. SoNRT3 partially compensated for ¹⁵${\mathrm{N}\mathrm{O}}_3^{-}$ uptake in atnrt2.1 and atnrt3.1 mutants. Transcriptome analysis showed that SoNRT3 may enhance nitrate uptake and root development by promoting the expression of high-affinity nitrate transporters, nitrogen assimilation, auxin signaling, and cell differentiation. Additionally, SoNRT3 can interact with a spinach NRT2 family protein (SoNRT2a), whose transcription level was also induced by low N and N deficiency. Together, this study clarifies the key roles and regulatory network of SoNRT3 in low-nitrate tolerance, which contributes to a novel understanding of nitrate utilization in spinach. Full article

Cereal/legume intercropping enhances legume nodulation and improves nitrogen use efficiency (NUE) in cereal crops. This facilitation of symbiotic nitrogen fixation (SNF) in intercropped legumes involves a complex eco-physiological mechanism driven by multiple factors. Among them, interspecific root interactions (IRIs) are a key factor influencing SNF in intercropped legumes. Currently, it remains unclear whether and how IRIs modulate SNF to affect NUE and yield formation in legume species. In this study, maize/pea intercropping with different types of root separation [no barrier (NB) and plastic barrier (PB)] and pea monocropping (IP) were simulated in a nitrogen (N)-free nutrient matrix in pots, and the SNF, N metabolism, and N partitioning were investigated. We demonstrated that IRIs optimize SNF performance. N assimilation is positively regulated following increases in enzyme activity and gene expression in intercropped roots and nodules. Furthermore, IRIs facilitate amino acid (AA) export from nodules to roots and shoots, which is followed by an increase in AA levels in leaves (source) and leaf exudates (sink). Overall, intensive SNF drives N metabolism and alters source-to-sink N partitioning, thereby increasing NUE (by 23%) and yield (by 15%) in intercropped pea. This study reveals the positive roles of IRIs to the NUE and yield and provides useful reference material for increasing N contents derived from SNF to maximize NUE and crop yields in intercropped legumes. Full article

The interactive effects between nano-silicon dioxide (n-SiO₂) and elevated CO₂ (eCO₂; 645 ppm) on soybean physiology, nitrogen fixation, and nutrient dynamics under climate stress remain underexplored. This study elucidates their combined effects under ambient (aCO₂; 410 ppm) and eCO₂ conditions. eCO₂ + n-SiO₂ synergistically enhanced shoot length (30%), total chlorophyll (112.15%), and photosynthetic rate (103.23%), alongside improved stomatal conductance and intercellular CO₂ (17.19%), optimizing carbon assimilation. Nodulation efficiency increased, with nodule number and biomass rising by 48.3% and 53.6%, respectively, under eCO₂ + n-SiO₂ versus aCO₂. N-assimilation enzymes (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase) surged by 38.5–52.1%, enhancing nitrogen metabolism. Concurrently, phytohormones (16–21%) and antioxidant activities (15–22%) increased, reducing oxidative markers (18–22%), and bolstering stress resilience. Nutrient homeostasis improved, with P, K, Mg, Cu, Fe, Zn, and Mn elevating in roots (13–41%) and shoots (13–17%), except shoot Fe and Zn. These findings demonstrate that n-SiO₂ potentiates eCO₂-driven benefits, amplifying photosynthetic efficiency, nitrogen fixation, and stress adaptation through enhanced biochemical and nutrient regulation. This synergy underscores n-SiO₂ role in optimizing crop performance under future CO₂-rich climates, advocating nano-fertilizers as sustainable tools for climate-resilient agriculture. Full article

Although drunken horse grass (Achnatherum inebrians) can be simultaneously infected by the foliar endophyte Epichloë gansuensis and colonized by Bacillus subtilis, it remains unclear whether Epichloë endophyte symbiosis influences B. subtilis colonization, as well as how their interaction affects nitrogen fixation and assimilation. The purpose of the present study was to investigate whether E. gansuensis endophyte infection facilitates the colonization of B. subtilis in the roots of host plants, with a focus on understanding the interaction effects of the E. gansuensis endophyte and B. subtilis on plant growth and nutrient absorption. In this study, we measured the colony growth rate of B. subtilis LZU7 when co-cultured with E. gansuensis strains. In addition to an in vitro test, we investigated the root colonization of Epichloë endophyte-infected plants (E+) and Epichloë endophyte-free plants (E−) with the GFP-tagged B. subtilis LZU7 in an inoculation test. Furthermore, we evaluated the interactions between E. gansuensis endophyte symbiosis and B. subtilis LZU7 colonization on the dry weight, nitrogen fixation, nitrogen converting-enzyme activity, and nutrients for E+ and E− plants by labeling with ¹⁵N₂. The results showed that the growth rates of B. subtilis LZU7 were altered and increased in a co-culture with the E. gansuensis endophyte. A significantly greater colonization of GFP-tagged B. subtilis LZU7 was detected in the roots of E+ plants compared with the roots of E− plants, suggesting that E. gansuensis endophyte symbiosis enhances the colonization of beneficial microorganisms. The combination of E. gansuensis endophyte symbiosis and B. subtilis LZU7 inoculation significantly altered the expression of the nitrogenase (nifH) gene, thereby promoting increased biological nitrogen fixation (BNF). The E. gansuensis endophyte infection and inoculation with B. subtilis LZU7 significantly increased δ15NAir in plants. Co-inoculation with the E. gansuensis endophyte and B. subtilis LZU7 significantly elevated NH₄⁺ accumulation in the roots, depleted the NH₄⁺ availability in the surrounding soil, and showed no measurable impact on the foliar NH₄⁺ content. The observed alterations in the NH₄⁺ content were linked to nitrogen-fixing microorganisms that promoted nitrogen fixation, thereby enhancing nitrogen uptake and contributing to greater biomass production in A. inebrians. Our findings highlighted the fact that a foliar symbiosis with the E. gansuensis endophyte enhances the recruitment of beneficial bacteria, and that the resulting interaction significantly impacts nitrogen fixation, assimilation, and allocation in host plants. Full article

Sugar beet is a nitrogen (N)-sensitive crop, and its N regulation and utilization are critical for enhancing productivity. Sugar beet seedlings at the two-true-leaf-pair stage were hydroponically grown in an artificial climate chamber. Leaves and roots from three seedlings per treatment were sampled at 10, 20, 25, and 30 days after exposure to N treatments (N5: 5 mmol/L, N10: 10 mmol/L, N15: 15 mmol/L, and N20: 20 mmol/L) to assess the effects of N supply level on growth, photosynthesis, and carbon and nitrogen metabolism. The results revealed a time-dependent dynamics in beet biomass accumulation, with N20 inducing chlorosis and necrosis symptoms by 10 days post-treatment (DPT), resulting in the lowest biomass. While N15 significantly promoted root biomass by 30 DPT, showing a 23.70% (root dry weight, RDW) increase over N20; chlorophyll content and gas exchange parameters-net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) exhibited significant N dependence, with N15 maintaining high chlorophyll level (0.78 mg/g) and photosynthetic rate (220.33 μmol/(m²·s). Nitrogen assimilation, as indicated by glutamine synthetase and glutamate synthetase activity (GS and GOGAT), was stronger under N15, promoting amino acid synthesis and root growth, whereas N20 inhibited enzyme activity. Carbon metabolism analysis revealed that N15-driven sucrose synthesis significantly increased root sucrose content, sucrose phosphate synthase and sucrose synthase activity (SPS and SS), optimizing source–sink allocation. Correlation analysis showed a positive relationship between leaf and root biomass (r = 0.91), and root sucrose content was positively correlated with GOGAT activity (r = 0.90), emphasizing the synergistic regulation of C/N metabolism. On the contrary, N20 led to disrupted C/N metabolic homeostasis, inhibited enzyme activity, and C/N distribution. These results indicated that the photosynthetic output, enzyme efficiency, and sucrose distribution were coordinated by nitrogen optimization, and the growth of sugar beet seedlings was optimized. Full article

Nitrogen (N) management and planting density critically influence rice (Oryza sativa L.) N use efficiency (NUE) and yield stability, though excessive inputs risk ecological and productivity constraints. This study investigated molecular adaptations in japonica rice Hongyang 5 under three N density regimens: high N/low density (HNLD), medium N/medium density (MNMD), and low N/high density (LNHD). Our previous studies found that the N absorption efficiency, antioxidant enzyme activity, and energy metabolism-related phenotypes of rice roots showed significant differences under different treatments. In this study, we found that root morphology, such as root length, root surface area, root volume, and average root diameter, also showed significant differences among different treatments. Based on this, we further integrated transcriptome and co-expression network analysis, revealing 40,218 expressed genes with differential expression patterns across treatments. Weighted gene co-expression network analysis (WGCNA) identified 13 modules, with the Turquoise and Blue modules notably demonstrating strong associations with N assimilation, antioxidant activity, and ATP metabolism. Ten hub genes emerged through intramodular connectivity analysis, including LOC_Os02g53130 (N metabolism), LOC_Os06g48240 (peroxidase activity), and LOC_Os01g48420 (energy transduction), with RT-qPCR validation confirming transcriptome-derived expression profiles. Functional characterization revealed synergistic coordination between Turquoise module N metabolic pathways and Blue module redox homeostasis, suggesting an integrated regulatory mechanism for root adaptation to N density interactions. These findings establish a gene-network framework that reveals the molecular regulatory network of crop responses to N nutrition and planting density and provides important theoretical support for N fertilizer management, population quality optimization, and variety breeding in precision agriculture. Full article

Effectively utilizing aquatic plants to absorb nitrogen from water bodies and convert it into organic nitrogen via nitrogen assimilation enzyme activity reduces water nitrogen concentrations. This serves as a critical strategy for mitigating agricultural non-point source pollution in the Yellow River Basin However, emergent plants’ rate and mechanism of uptake of different forms of nitrogen remain unclear. This study determined the nitrogen uptake rates, nitrogen assimilation activities, root properties, and photosynthetic parameters of four emergent plants, Phragmites australis, Typha orientalis, Scirpus validus, and Lythrum salicaria, under five NH₄⁺/NO₃⁻ ratios (9:1, 7:3, 5:5, 3:7, and 1:9) using ¹⁵N hydroponic simulations. The results demonstrated that both the form of nitrogen and the plant species significantly influenced the nitrogen uptake rates of emergent plants. In water bodies with varying NH₄⁺/NO₃⁻ ratios, P. australis and T. orientalis exhibited significantly higher inorganic nitrogen uptake rates than S. validus and L. salicaria, increasing by 11.83–114.69% and 14.07–130.46%, respectively. When the ratio of NH₄⁺/NO₃⁻ in the water body was 9:1, the uptake rate of inorganic nitrogen by P. australis reached its peak, which was 729.20 μg·N·g⁻¹·h⁻¹ DW (Dry Weight). When the ratio of NH₄⁺/NO₃⁻ was 5:5, the uptake rate of T. orientalis was the highest, reaching 763.71 μg·N·g⁻¹·h⁻¹ DW. The plants’ preferences for different forms of nitrogen exhibited significant environmental plasticity. At an NH₄⁺/NO₃⁻ ratio of 5:5, P. australis and T. orientalis preferred NO₃⁻-N, whereas S. validus and L. salicaria favored NH₄⁺-N. The uptake rate of NH₄⁺-N by the four plants was significantly positively correlated with glutamine synthetase and glutamate synthase activities, while the uptake rate of NO₃⁻-N was significantly positively correlated with NR activity. These findings indicate that the nitrogen uptake and assimilation processes of these four plant species involve synergistic mechanisms of environmental adaptation and physiological regulation, enabling more effective utilization of different nitrogen forms in water. Additionally, the uptake rate of NH₄⁺-N by P. australis and T. orientalis was significantly positively correlated with glutamate dehydrogenase (GDH), suggesting that they are better adapted to eutrophication via the GDH pathway. The specific root surface area plays a crucial role in regulating the nitrogen uptake rates of plants. The amount of nitrogen uptake exerted the greatest total impact on the nitrogen uptake rate, followed by root traits and nitrogen assimilation enzymes. Therefore, there were significant interspecific differences in the uptake rates of and physiological response mechanisms of emergent plants to various nitrogen forms. It is recommended to prioritize the use of highly adaptable emergent plants such as P. australis and T. orientalis in the Yellow River irrigation area. Full article

The increasing pollution of polystyrene (PS) and polymethyl methacrylate (PMMA) microplastics (MPs) has become a global marine environmental problem. Diatoms contribute nearly 40% of marine primary productivity and shape the nitrogen cycle in the oceans. However, the persistence of the phytotoxicity of MPs on diatoms, especially nitrogen assimilation, remains largely unknown. To examine the persistence of PS and PMMA toxicity in diatoms, two subexperiments (a 96 h exposure followed by a recovery phase) were conducted on Thalassiosira pseudonana at concentrations ranging from 0.001 to 1 mg/L. The results showed that PS and PMMA inhibited algal growth by 3.76–6.49% and 4.44–8.37%; increased oxidative stress by 10.06–30.51% and 30.46–38.12%; and caused ultrastructural damage by 14.24–25.56% and 12.28–20%, respectively, consistent with the downregulation of glyoxylate, dicarboxylate metabolism, and glutathione metabolism. At the recovery stage, the algal density induced by PS was significantly recoverable at 0.001 and 0.01 mg/L, consistent with the enhanced carbohydrate metabolisms. After recovery, the cell permeability and reactive oxygen species (ROS) levels induced by PS and PMMA were significantly decreased at 1 mg/L, respectively, which was closely related to the downregulation of glycine, serine, and threonine metabolism and the upregulation of pantothenate and coenzyme A biosynthesis. Moreover, the inhibition of nitrogen assimilation enzymic activities induced by PS and PMMA was significantly recovered at 1 mg/L despite the downregulation of nitrogen metabolism. This study highlights the phenomena and mechanisms of phytotoxicity and recovery, and provides new insights for comprehensive understanding and evaluation of environmental risks of MPs. Full article

This article methodically reveals how, in woody plants (poplar), the interaction between N and P coordinates root structure and nutrient absorption through a complex hormone signaling network. This study bridges a significant gap in our knowledge of nutrient interaction networks. The results demonstrate that NO₃⁻ significantly enhances the gene expression and enzymatic activity of organic acid synthases (MDH, PEPC) and APs. Furthermore, it synergizes with IAA/ABA signals to refine root structure, enhancing the surface area for P absorption. In low Pi availability environments, NO₃⁻ further promotes P recycling by simultaneously boosting the levels of Pi transport proteins (notably, the PHO family), facilitating myo-inositol phosphate metabolism (via IMP3/ITPK1-mediated PP-InsPs degradation), and augmenting IAA/SA signals. Pi induces the activity of N assimilation enzymes (GS/GOGAT/GDH), facilitating nitrogen metabolism. However, in the absence of N, it leads to a metabolic imbalance characterized by high enzymatic activity but low efficiency. Alternatively, adequate N availability allows Pi to improve root robustness and N assimilation efficiency, mediated by IAA/GA accumulation and ABA signaling (e.g., SNRK2/ABF). We propose the existence of an intricate network in poplar, orchestrated by transcriptional cascades, metabolic regulation, and hormonal synergism. Key modules such as SPX-PHR, NLA, HHO2, and MYB59 are likely central to this network’s function. These findings offer a foundational framework for the development of molecular breeding and precise fertilization strategies, enhancing the efficient use of N and P in forestry. Full article

Vitamin C industrial residue after evaporation (RAE) acts as both a rapid-release carbon source and a microbial activity promoter. A two-year maize field experiment assessed the effectiveness of RAE in improving soil quality in degraded semi-arid regions. The RAE formulation was applied via drip irrigation during the sixth true leaf unfolded (BBCH 24), fourteenth true leaf unfolded (BBCH 38), and middle of grain filling (BBCH 66) stages, which consisted of three treatments: (1) untreated control (CK), (2) low RAE rate (LR: 150 L/ha), and (3) high RAE rate (HR: 300 L/ha). Soil physicochemical properties, enzyme activities, maize nutrient accumulations, and yields were comprehensively analyzed at the maize maturity stage. RAE application significantly improved the following soil nutrients: dissolved organic carbon (10.40–25.92%), ammonium nitrogen (14.04–70.67%), nitrate nitrogen (14.80–78.63%), and available phosphorus (11.79–42.55%). Soil enzyme activities also increased: sucrase (12.38–30.25%), amidase (1.95–25.69%), peptidase (0.56–48.79%), β-1,4-N-acetylglucosaminidase (3.11–9.48%), protease (17.41–226.29%), and acid phosphatase (8.73–60.04%). These changes enhanced maize nitrogen (17.63–40.73%) and phosphorus (20.09–42.11%) uptake, increasing yield by 7.12–13.46%. Statistical analysis showed strong correlations between yields and nutrient accumulations (r = 0.82, p < 0.01), particularly phosphorus (r = 0.91, p < 0.001). RAE enhances crop productivity in degraded agricultural systems by improving soil nutrient availability and plant assimilation, making it a viable alternative to conventional fertilizers. Full article

The use of nickel (Ni) as a fertilizer remains a topic of debate, particularly in non-legume species, as Ni is required only in trace amounts for optimal plant function. Urea application in plants, whether foliar or root-based, relies on the urease enzyme to convert urea into NH_4⁺ and CO₂, with Ni serving as an essential cofactor. In this study, we conducted an experiment using a 2 × 2 factorial design, combining two urea concentrations [4% and 8% (w/v)] with the absence or presence of Ni (0.3 g L⁻¹ supplied as NiSO₄·6H₂O). Gas exchange parameters were measured two days after fertilization. We quantified urease enzyme activity, urea content, photosynthetic pigments, carbohydrates, and other nitrogenous metabolites. The presence of Ni during foliar urea fertilization significantly increased the photosynthetic rate and photosynthetic pigments, which we attributed to improved urea assimilation. The combination of urea and Ni enhanced urease activity, leading to higher levels of various nitrogenous metabolites. Ni positively influenced foliar urea assimilation, promoting its conversion into organic compounds, such as proteins, while mitigating the toxic effects associated with urea accumulation. Full article

Nitrogen fertilizers in agriculture often suffer losses. Ammonia-assimilating bacteria can immobilize ammonia and reduce these losses, but they have not been used in agriculture. This study identified an ammonia-assimilating strain, Enterobacter sp. B12, which assimilated ammonia via the glutamate dehydrogenase (GDH) pathway at low levels (5 mM) and the glutamine synthetase (GS)-glutamine-2-oxoglutarate aminotransferase (GOGAT) pathway at high levels (10 mM). Inoculating wheat with B12 increased seedling dry weight, nitrogen accumulation, rhizosphere soil nitrogen content, and root enzyme activities, including GDH, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), under both conditions. However, root GS, GOGAT enzyme activities, and ammonia assimilation-related gene expressions were lower than the controls. The results suggest that the ammonia-assimilating bacterium promotes wheat growth, nitrogen accumulation, and soil nitrogen immobilization by establishing an ammonia and amino acid exchange with roots and enhancing root antioxidant capacity, making it a potential plant growth-promoting rhizobacteria (PGPR). Full article