Higher Nitrogen Use Efficiency Research Articles

Exploring the Molecular Landscape of Nitrogen Use Efficiency in Potato (Solanum tuberosum L.) under Low Nitrogen Stress: A Transcriptomic and Metabolomic Approach

Enhancing crop nitrogen use efficiency (NUE) in agricultural sciences is a pivotal challenge, particularly for high-demand crops like potatoes (Solanum tuberosum L.), the world’s third most significant food crop. This study delves into the molecular responses of potatoes to low nitrogen (LN) stress, employing an integrative approach that combines transcriptomics and metabolomics to compare two cultivars with divergent NUE traits: XS6, known for its high NUE, and NS7, characterized by lower NUE. Our research unveils that XS6 exhibits higher chlorophyll and N content, increased tuber yield, and elevated N assimilation capacity under LN stress conditions compared to NS7. Through transcriptome analysis, we identified critical genes involved in C and N metabolism that had higher expression in XS6. A significant discovery was the high-affinity nitrate transporter 2.7 gene, which showed elevated expression in XS6, suggesting its key role in enhancing NUE. Metabolomics analysis further complemented these findings, revealing a sophisticated alteration of 1252 metabolites under LN stress, highlighting the dynamic interplay between carbon and N metabolism in coping with N scarcity. The integration of transcriptomic and metabolomic data underscored the crucial role of trehalose in mitigating N deficiency and enhancing NUE. This study provides novel insights into the molecular mechanisms governing NUE in potatoes, offering valuable perspectives for molecular breeding to enhance NUE in potatoes and potentially other crops.

Short-Term Effect of the Combined Application of Rice Husk Biochar and Organic and Inorganic Fertilizers on Radish Growth and Nitrogen Use Efficiency.

Research on soil biochar fertilization has mainly been conducted on cereal crops, and information on its potential for radish production remains inconsistent. Therefore, a pot experiment was conducted to examine the short-term effects of rice husk biochar on radish growth and nitrogen use efficiency (NUE). An investigation was conducted with two application rates of biochar alone, (10 t ha-1 (B10) and 25 t ha-1 (B25), and biochar + chicken manure application with and without NPK fertilizer. The results indicated that the application of biochar 25 t ha-1 + chicken manure (B25:CHM) and the combination of biochar 25 t ha-1 + chicken manure + NPK fertilizer (B25:CHM:NPK) significantly increased root yield by improving NUE, fertilizer recovery efficiency (REN), agronomic efficiency (AE), nitrogen harvest index (NHI), and retaining soil NH4+-N. Although biochar application alone did not significantly influence radish growth on a short-term basis, B10 and B25 increased root yields by 10% and 20%, respectively, compared with the control. Notably, the role of biochar application when combined with organic and inorganic fertilizers was to retain fertilizer N and promote N uptake efficiency by radishes, as higher rates of biochar resulted in higher NUE. Our results suggest that B25:CHM is a suitable combination for organic farming.

Comparative phenotypic and transcriptomic analysis reveals genotypic differences in nitrogen use efficiency in sorghum

Sorghum (Sorghumbicolor L.), a model for C4 grass and an emerging biofuel crop, is known for its robust tolerance to low input field. However, the focus on enhancing nitrogen use efficiency (NUE) in sorghum under low nitrogen (N) conditions has been limited. This study conducted hydroponic experiments and field trials with two sorghum inbred lines, contrasting in their N efficiency: the N-efficient (398B) and the N-inefficient (CS3541) inbred lines. The aim was to analyze the key factors influencing NUE by integrating phenotypic, physiological, and multi-omics approaches under N deficiency conditions. The field experiments revealed that 398B displayed superior NUE and yield performance compared to CS3541. In hydroponic experiments, the growth of 398B outperformed CS3541 following N deficiency, attributing to its higher photosynthetic and sustaining activity of N metabolism-related enzymes. Genomic and transcriptomic integration highlighted fewer genomic diversities and alterations in global gene expression in 398B, which were likely contributor to its high NUE. Additionally, co-expression network analysis suggested the involvement of key genes which impact N uptake efficiency (NUpE) and N utilization efficiency (NUtE) in both lines, such as an N transporter, Sobic.003G371000.v3.2leaf(NPF5.10) and a transcription factor, Sobic.002G202800.v3.2leaf(WRKY) in bolstering NUE under low-N stress. The findings collectively suggested that 398B achieved higher NUpE and NUtE, effectively coordinating photosynthesis and N metabolism to enhance NUE. The candidate genes regulating N uptake and utilization efficiencies could provide valuable insights for developing sorghum breeds with improved NUE, contributing to sustainable agricultural practices and bioenergy crop development.

BjuB05.GS1.4 promotes nitrogen assimilation and participates in the domestication of shoot NUE in Brassica juncea

Elucidating crops' physiological and molecular mechanisms to adapt to low nitrogen environment and promoting nitrogen transfer from senescent leaves to new leaves is crucial in improving Brassica's nitrogen use efficiency (NUE). Glutamine synthetase (GS), a vital gene that helps plants to reassimilate ammonium released from protein degradation in leaves, was the focus of our research. In this study, we identified high (H141) and low NUE genotype (L65) genotypes of Brassica juncea with different responses to low-nitrogen stress. We observed that H141 has a lower nitrate content but higher ammonium and free amino acid contents as well as higher nitrate reductase and GS activities in the shoots. These physiological indicators are responsible for the high NUE of H141. Whole-genome resequencing data revealed that 5,880 genes associated with NUE are polymorphic between H141 and L65. These genes participate in amino acid, carbohydrate, and energy metabolic pathways. Haplotype analysis revealed two haplotypes for BjuB05.GS1.4. Hap1 and Hap2 have multiple single nucleotide polymorphisms or insertions/deletions in the regulatory regions of 5′ and 3′ untranslated regions and introns. Furthermore, the shoot NUE of Hap1 is significantly lower than that of Hap2. The two haplotypes of BjuB05.GS1.4 led to differences in the shoot NUEs of different genetic populations of mustard and are associated with the local soil nitrogen content, suggesting that they might help mustard to adapt to different geographies. In conclusion, the results of our study shed light on the physiological and molecular mechanisms underlying different mustard NUE genotypes and demonstrate the enormous potential of NUE breeding in B.juncea.

Straw returning and nitrogen reduction: Strategies for sustainable maize production in the dryland

Implementing continue straw returning practices and optimizing nitrogen application can mitigate nitrogen losses and enhance nitrogen use efficiency (NUE) in dryland. 15N-labeled technique offers a robust approach for tracking fertilizer nitrogen fate and assessing nitrogen use efficiency. Based on the continue (>6 yr) experiment, we conducted a two-year experiment (2020 and 2021) to evaluate the effects of straw returning and nitrogen management under plastic film mulching on 15N recovery rates, N2O emissions and maize yield with three treatments: no straw returning with 225 kg N·ha−1 under plastic film mulching (RP-N225), straw returning with 225 kg N·ha−1 under plastic film mulching (RPS-N225), and straw returning with 20% nitrogen reduction (180 kg N·ha−1) under plastic film mulching (RPS-N180). After six years, both continue straw returning with plastic film mulching increased uptake of fertilizer nitrogen, had higher 15N recovery rates than RP-N225, leading to increased 15N accumulation in grain and aboveground biomass, ultimately enhancing yield. The RPS-N225 treatment exhibited the highest spring maize yield and nitrogen harvest index. The RPS-N180 treatment significantly increased maize yield more than RP-N225 and had the highest NUE, partial factor productivity of nitrogen fertilizer, and nitrogen uptake efficiency, with improvements ranging from 1.7 to 2.4%, 19.3–29.6%, and 17.3–27.5%, respectively, compared to the other treatments. Moreover, RPS-N225 resulted in significantly higher cumulative N2O emissions and yield-scaled N2O emissions than the other treatments, whereas the RPS-N180 treatment significantly decreased yield-scaled N2O emissions compared to RP-N225. Hence, combining continue straw returning with appropriate nitrogen reduction can effectively increase maize yield and yield-scaled N2O emissions. By offering insights into optimizing nitrogen fertilizer management after continue maize straw return, this study is contributed to widespread adoption of straw return practices and sustainable agricultural development in semi-arid areas.

The elite haplotype OsGATA8-H coordinates nitrogen uptake and productive tiller formation in rice

Excessive nitrogen promotes the formation of nonproductive tillers in rice, which decreases nitrogen use efficiency (NUE). Developing high-NUE rice cultivars through balancing nitrogen uptake and the formation of productive tillers remains a long-standing challenge, yet how these two processes are coordinated in rice remains elusive. Here we identify the transcription factor OsGATA8 as a key coordinator of nitrogen uptake and tiller formation in rice. OsGATA8 negatively regulates nitrogen uptake by repressing transcription of the ammonium transporter gene OsAMT3.2. Meanwhile, it promotes tiller formation by repressing the transcription of OsTCP19, a negative modulator of tillering. We identify OsGATA8-H as a high-NUE haplotype with enhanced nitrogen uptake and a higher proportion of productive tillers. The geographical distribution of OsGATA8-H and its frequency change in historical accessions suggest its adaption to the fertile soil. Overall, this study provides molecular and evolutionary insights into the regulation of NUE and facilitates the breeding of rice cultivars with higher NUE.

Effects of Different Doses of Nitrogen on Growth and Nitrogen Use Efficiency of Maize (Zea mays L.) in Berekum Municipality of Ghana

Background: Adequate and balanced use of plant nutrients could increase crop performance and reduce adverse environmental effects. Farmers in Berekum have little information on the specific rate of nutrient, especially nitrogen application for hybrid and open pollinated maize varieties. Methods: A field experiment was carried out in Berekum Municipality of Ghana to determine the effects of different doses of N fertilizer (0, 90, 120 and 150 kg N ha-1) on growth and nitrogen use efficiency (NUE) of Pannar 12 (hybrid) and Omankwa (open-pollinated) maize varieties. The experiment was conducted in a factorial randomized block design and replicated thrice. Result: Experimental results revealed that incremental doses of nitrogen significantly impacted vegetative growth and NUE of maize. The studies indicated that the growth response in terms of plant height, number of leaves per plant and stem diameter of Omankwa was better than that of Pannar 12. It was found that in the main cropping period of 2019, the maximum NUE of 14.58 kg/kg was gained when Pannar 12 was grown with 150 kg N ha-1, while the highest NUE (15.91 kg/kg) was recorded when Omankwa was grown with 90 kg N ha-1. In the minor season of 2019, NUE was highest (13.54 kg/kg) when Pannar 12 was grown with 150 kg N ha-1, while application of 120 kg N ha-1 to Omankwa resulted in the highest NUE (10.85 kg/kg). The studies indicated that application of nitrogen at 90, 120 and 150 kg N ha-1 improved NUE in maize. However, NUE was optimized in Pannar 12 due to application of 150 kg N ha-1, while application of 90 kg N ha-1 was enough to optimize NUE in Omankwa.

Strong regulation of nitrogen supply and demand in a key desert legume tree

High abundance of legumes in drylands suggests that symbiotic nitrogen fixation provides an advantage in water-limited environments. However, the interactive effect of nitrogen availability and water scarcity on the nitrogen fixation strategies of dryland legumes remain largely unexplained. We conducted two experiments to test the effects of nitrogen availability and drought on symbiotic nitrogen fixation in two drought-adapted Acacia tree species. Seedlings were grown under deficient and sufficient levels of nitrogen and with and without an imposed drought to test the effect of resource availability on nitrogen fixation and plant growth. We found that seedlings that grew in extreme deficiency of nitrogen reached a similar biomass as seedling that grew with a sufficient supply of nitrogen, showing a high nitrogen-use efficiency. Nitrogen fixation was strongly downregulated (reduction of 90% in biomass allocation to nodules) when plants received sufficient nitrogen supply. Under nitrogen deficiency, drought had a slight negative effect on nodule biomass and total biomass. Under sufficient nitrogen, drought reduced nitrogen availability enough to induce an increase in symbiotic nitrogen fixation in the risk-averse A. raddiana but not in the risk-taking A. tortilis. We conclude that strong regulation of nitrogen fixation together with low nitrogen demand, and flexible strategies of carbon and nitrogen allocation, increase the chance of legume tree survival and establishment in dry and unpredictable environments.

Agronomic and physiological characteristics of high yield and nitrogen use efficient varieties of rice: Comparison between two near‐isogenic lines

AbstractIncreasing the application of nitrogen fertilizer is the main approach to increase rice production, but it also brings problems of environmental pollution and increases agricultural production costs. Cultivating high‐yielding and high nitrogen use efficiency (NUE) rice varieties is an important approach to solving this problem. The rice varieties carrying dep1 (dense and erect panicle 1) have both high grain yield and high NUE. However, their plant traits have not been fully explored. In this study, two rice near‐isogenic lines carrying dep1 (NIL‐DEP1 and NIL‐dep1) were grown in paddy fields under 0, 120 and 270 kg N ha−1. We analyzed agronomic traits of panicle type, plant type, leaves and roots, and physiological traits of vascular bundles, photosynthetic rate and carbon and nitrogen transport. The results showed that the NIL‐dep1 exhibited higher grain yield and NUE than NIL‐DEP1, mainly due to the higher spikelet number per panicle, grain filling percentage and dry matter production. Compared with NIL‐DEP1, NIL‐dep1 had improved flag leaf morpho–physiological traits, including erect flag leaves, greater leaf thickness and specific leaf weight, higher root dry weight, root length, root volume and root surface area, and a better canopy structure, as reflected by a lower light interception percent and canopy extinction coefficient, leading to better photosynthetic performance and dry matter production. In addition, NIL‐dep1 exhibited better vascular bundle traits of peduncle and enhanced dry matter, stem carbon and nitrogen translocation during grain filling. In conclusion, NIL‐dep1 had high grain yield and NUE by improved agronomic and physiological traits and increasing carbon and nitrogen translocation during grain filling. These traits mentioned above could be used to select and breed high grain yield with high NUE rice varieties.

Effects of different stocking density start-up conditions on water nitrogen and phosphorus use efficiency, production, and microbial composition in aquaponics systems

Controlling environmental parameters, including nitrogen and phosphorus use efficiency, is a crucial aspect of maintaining effective aquaponic systems. In this study, we evaluated the impact of start-ups under high (20 kg/m3) and low (5 kg/m3) stocking density conditions on water quality, productivity, nitrogen use efficiency (NUE), phosphorus use efficiency (PUE), microbial community compositions, and functional genes in the aquaponics system. Six experimental units (three replications per treatment) were categorized into two groups. The experimental process was divided into two phases: Phase I (Days 1–40) and Phase II (Days 41–145). During Phase I, the two system groups were initiated under high and low stocking densities. Phase II constituted the fish and vegetable production phase, with all aquaponics systems standardized at a stocking density of 10 kg/m3 and a planting density of 12 plants/m2. The results indicated superior water quality in the low aquaponics systems than that in the high aquaponics systems during Phase I, whereas the opposite was observed during Phase II. The final weight, specific growth rate, and fish weight gain of jade perch (Scortum barcoo), as well as the plant weight gain of tomato plants, were significantly higher in the high aquaponics system than those in the low aquaponics system. The NUE and PUE of the high aquaponics system were 49.55 ± 1.02% and 60.12 ± 1.28%, respectively, surpassing those of the low aquaponics system (43.41 ± 2.16% and 49.06 ± 1.59%). The microbial diversity in the moving bed biofilm reactor and roots of the high aquaponics system was lower than in the low aquaponics system. However, the relative abundances of nitrifying and denitrifying bacteria were higher than those in the low aquaponics system. The number of copies of functional genes for nitrification and denitrification, including amoA, nxrB, nirS, nirK, and nosZ, was higher in the high aquaponics systems. Overall, the results indicated that high aquaponics systems initiated with high stocking density yield more products, improved water quality, and higher NUE and PUE by altering the composition of microbial communities. This study presents a method for enhancing the functional microbial community of a system by optimizing conditions during the initiation period.

Unraveling differential characteristics and mechanisms of nitrogen uptake in wheat cultivars with varied nitrogen use efficiency

Nitrogen uptake is crucial to wheat nitrogen use efficiency (NUE). The study's findings indicate that both high- and low-NUE cultivars exhibited highest nitrogen uptake efficiency (NupE) under 0.2 mM nitrogen. Under 2 mM nitrogen, their NupEs decrease significantly, while uptakes to NO3− were notably higher than that of NH4+. Strikingly, high-NUE cultivars exhibited a significantly higher NH4+ uptake rate than low NUE cultivars, resulting in a marked improvement in their ability to take up nitrogen. The NUEs of the cultivars with 5 mM nitrogen were almost half that of 2 mM nitrogen. NO3− uptake primarily occurred in the mature zone of roots, while NH4+ uptake took place in the root tip meristem and elongation zones. Notably, the NH4+ uptake in root tip meristematic zone of high-NUE cultivar was significantly higher than that of low NUE cultivar. Furthermore, the NO3− uptake of high-NUE cultivar in the root mature zone was significantly higher than that of low-NUE cultivar under 2 mM nitrogen. These findings were consistent with the significantly higher expression levels of TaAMT in root tip and of TaNRT in root mature area of high-NUE cultivar compared to low-NUE cultivar, respectively, enabling efficient absorption of NO3− and NH4+ and transport of NO3− to shoot. The high-NUE cultivars showed elevated expression of amino acid transporters further promoting nitrogen uptake, and conversion of nitrogen into ureides and amino acids further facilitated inorganic nitrogen uptake by roots. The differential findings offer valuable insights into novel variety breeding of high NUE in the future.

Enhancing nitrogen use efficiency and plant productivity in long-term precrop/crop rotation and fertilization management

ContextLong-term experiments are an important tool to investigate the effects of crop rotation and fertilization measures under climate change conditions. However, there are few studies on nitrogen use efficiency (NUE) of crops in long-term cropping systems in Europe, but no consolidate studies in Germany. ObjectiveWe analyzed a long-term experiment established in 1982 to observe the role of legumes on total nitrogen uptake, NUE, agronomic efficiency, nitrogen response index and N recovery efficiency compared to fallow land and cereals in a crop rotation over the long-term. MethodsThe experiment included five different precrops (fallow land, maize, oat, field bean and clover mulch) in combination with four levels of fertilization (control, PK, PK+N with reduced dosage, and PK+N with full dosage followed by three years of cereal cultivation (winter wheat, winter rye, summer barley) in all treatments. The field trial was conducted as a fully factorial split plot design, with spatially randomized field repetitions in four blocks. ResultsLong-term mineral NPK fertilization improved the N uptake of winter wheat (185.7 kg N ha−1), winter rye (152.2 kg N ha−1) and summer barley (92.2 kg N ha−1) when the higher level of fertilization (NPK 100%) was implemented. A year-round application of clover mulch as green manure in the rotational system resulted in higher NUE (up to 37%) compared to fallow land after 40 years. Crop rotation with oat and maize (100% cereals) led to lower NUE (up to 30%) compared to fallow land. Clover mulch (198%), field bean (155%), fallow land (148%) and maize (119%) significantly increased the N uptake of wheat compared to oat in 2015. Over time, the agronomic efficiency was increased. This increase was 4 or 5 times higher in the 9th and 10th crop rotation compared to the beginning of the experiment (in 1983). Nitrogen response index of clover mulch was approximately 33–37% lower than fallow land at the beginning of the experiment in 1983 and 45–50% lower over the 40 years. N recovery efficiency values of winter wheat (94%), winter rye (66%) and summer barley (46%) increased within the 10th crop rotation compared to the beginning of the long-term experiment. ConclusionsCombining clover mulch as a green manure with mineral fertilizer has greater potential to improve NUE and crop productivity by increasing soil N availability. ImplicationsOur study highlights the importance of evaluating agronomic management practices in long-term field experiments to understand their sustainable effects.

Integrated physiological, biochemical, and transcriptomics analyses reveal the underlying mechanisms of high nitrogen use efficiency of black sesame

Cultivating high nitrogen use efficient varieties is a sustainable solution to mitigating adverse effects on the environment caused by excessive nitrogen fertilizer application. However, in sesame, although immoderate nitrogen fertilizers are used to promote yield, the molecular basis of high nitrogen use efficiency (NUE) is largely unknown. Hence, this study aimed to identify high NUE black sesame variety and dissect the underlying physiological and molecular mechanisms. To achieve this, seventeen seedling traits of 30 black sesame varieties were evaluated under low nitrogen (LN) and high nitrogen (HN) conditions. Dry matter accumulation, root parameters, shoot nitrogen accumulation, and chlorophyll content are important factors for evaluating the NUE of sesame genotypes. The variety 17–156 was identified as the most efficient for N utilization. Comparative physiological and transcriptomics analyses revealed that 17–156 possesses a sophisticated nitrogen metabolizing machinery to uptake and assimilate higher quantities of inorganic nitrogen into amino acids and proteins, and simultaneously improving carbon metabolism and growth. Specifically, the total nitrogen and soluble protein contents significantly increased with the increase in nitrogen concentrations. Many important genes, including nitrate transporters (NPFs), amino acid metabolism-related (GS, GOGAT, GDH, etc.), phytohormone-related, and transcription factors, were significantly up-regulated in 17–156 under HN condition. In addition, 38 potential candidate genes were identified for future studies toward improving sesame's NUE. These findings offer valuable resources for deciphering the regulatory network of nitrogen metabolism and developing sesame cultivars with improved NUE.

Regional nitrogen budgets of agricultural production systems in Austria constrained by natural boundary conditions

Nitrogen (N) budgets are valuable tools to increase the understanding of causalities between agricultural production and N emissions to support agri-environmental policy instruments. However, regional agricultural N budgets for an entire country covering all major N flows across sectors and environmental compartments, which also distinguish between different N forms, are largely lacking. This study comprehensively analyses regional differences in N budgets pertainting to agricultural production and consumption in the largely alpine and spatially heterogeneous country of Austria. A special focus is on the interconnections between regional agricultural production systems, N emissions, nitrogen use efficiencies (NUE), and natural boundary conditions. Seven regional and one national balance are undertaken via material flow analysis and are analysed with regards to losses into soils, water bodies and atmosphere. Further, NUE is calculated for two conceptual systems of plant and plant-livestock production. The results reveal major differences among regions, with significant implications for agri-environmental management. The high-alpine region, characterized by alpine pastures with a low livestock density, shows consequent low N inputs, the lowest area-specific N outputs and the most inefficient NUE. In contrast, the highest NUE is achieved in a lowland region specialized in arable farming with a low livestock density and a predominance of mineral fertilizer over manure application. In this region, the N surplus is almost as low as in the high-alpine region due to both significantly higher N inputs and outputs compared to the high-alpine region. Nevertheless, due to low precipitation levels, widespread exceedances of the nitrate target level concentration take place in the groundwater. The same issue arises in another non-alpine region characterized by arable farming and high livestock densities. Here, the highest N inputs, primarily via manure, result in the highest N surplus and related nitrate groundwater exceedances despite an acceptable NUE. These examples show that NUE alone is an insufficient target and that adapted criteria are needed for different regions to consider natural constraints and specific framework conditions. In a geographically heterogeneous country like Austria, the regional circumstances strongly define and limit the scope and the potential effectiveness of agricultural N management strategies. These aspects should be integrated into the design, assessment and implementation of agri-environmental programmes.

Single-Time Mechanical Deep Placement Fertilization Using Bulk Blending Fertilizer on Machine-Transplanted Rice: Balanced Yield, Nitrogen Utilization Efficiency, and Economic Benefits

Despite growing interest in controlled-release N fertilizers (CRNFs) because of their potential for enhancing nitrogen use efficiency (NUE) and economic returns, their comprehensive impact on machine-transplanted rice remains to be understudied. To address this gap, here, we present a two-year field experiment that assessed the impact of CRNF using mechanical deep placement fertilization (DPF) on rice cultivation. The study involved three CRNF types (bulk blending fertilizer (BBF), polymer-coated urea (PCU), and sulfur-coated urea (SCU)) and two fertilization methods (DPF and broadcast application), with a high-yield split fertilization of urea as a control (CK). The results showed that DPF, especially with SCU, greatly enhanced soil NH4+-N concentrations, NUE, rice yield, and economic benefits compared to broadcast application. BBF consistently exhibited superior NUE and notable economic benefits, regardless of the application method used. Conversely, single-time application of PCU was less favorable for rice growth. In conclusion, for optimal economic benefits and NUE, DPF combined with single-time application of SCU is recommended. However, if deep application is not feasible and only broadcasting is possible in rice cultivation, BBF emerges as the ideal choice for both high NUE and significant economic returns. This research offers insights for improved nitrogen management in machine-transplanted rice, effectively optimizing yield, NUE, and profitability.

Rapid Visual Detection of High Nitrogen-Use Efficiency Gene OsGRF4 in Rice (Oryza sativa L.) Using Loop-Mediated Isothermal Amplification Method.

The GROWTH-REGULATING FACTOR4 (OsGRF4) allele is an important target for the development of new high nitrogen-use efficiency (NUE) rice lines that would require less fertilizers. Detection of OsGRF4 through PCR (polymerase chain reaction)-based assay is cumbersome and needs advanced laboratory skills and facilities. Hence, a method for conveniently and rapidly detecting OsGRF4 on-field is a key requirement for further research and applications. In this study, we employed cleaved amplified polymorphic sequences (CAPs) and loop-mediated isothermal amplification (LAMP) techniques to develop a convenient visual detection method for high NUE gene OsGRF4NM73 (OsGRF4 from the rice line NM73). The TC→AA mutation at 1187-1188 bp loci was selected as the target sequence for the OsGRF4NM73 allele. We further employed this method of identification in 10 rice varieties that carried the OsGRF4 gene and results revealed that one variety (NM73) carries the target OsGRF4NM73 allele, while other varieties did not possess the osgrf4 genotype. The optimal LAMP reaction using hydroxynaphthol blue (HNB), a chromogenic indicator, was carried out at 65 °C for 60 min, and the presence of OsGRF4NM73 allele was confirmed by color changes from violet to sky blue. The results of this study showed that the LAMP method can be conveniently and accurately used to detect the OsGRF4NM73 gene in rice.

Optimal fertilizer rates towards the improvement of nitrogen use efficiency and reduction of nitrogen export in paddy rice-wheat intensive farming

Introduction: Fertilizer application above plant nitrogen (N) requirements, leading to N use inefficiency, has become the primary source of N surplus, posing nonpoint pollution threats. Chao Lake has received N loadings, primarily from the agroecosystem that surrounds it. Based on 10 years of field monitoring and experiment, this study used optimum fertilizer rates (30% N reduction) to evaluate nitrogen use efficiency (NUE) and N export in the Chao Lake watershed of paddy rice-wheat rotational farming.Methods: Five treatments were tested, namely, the Blank Treatment (CK), Conventional Fertilization Treatment (CFT), High Fertilization Treatment (HFT), Reduced Fertilization Treatment (CFT), Reduced Fertilization Treatment plus Straw addition (RFTS). The parameters employed to measure NUE were 1) by calculating NUE indicators; Agronomic efficiency (kg kg-1), recovery efficiency (%), and partial factor productivity (kg kg-1) 2) using the European Union NUE framework as a comparison tool. N export was measured using N export parameters, namely, nitrogen loading (kg ha-1yr-1), nitrogen runoff loss ratio (%), and net nitrogen runoff loss ratio (%).Results and discussion: Results revealed that optimum N fertilizer input levels maintained high crop and biomass yields. The empirical model of y = y0 + a * exp (−0.5 * (x-x0)/b2) explains the relationships between input N fertilizer and corresponding yield returns. Low yield responses to increased N input beyond certain limits were observed, which may lead to N accumulations. N export was much lower from the reduced fertilization treatments than other treatments. N export increased in 10 years for both paddy rice and wheat seasons. Runoff volume influenced N export more than any other environmental factor studied.Conclusion: Overall, optimal fertilizer levels produced high NUE, maintained high economic yield, and produced lesser N exports; NUE was in the order of reduced > high > conventional fertilization treatments, while it decreased in 10 years (2008–2018) across all treatments. Such strategies that further reduce fertilizer levels by accounting for excess supplies are vital for consolidating effective N control measures.

Genome-wide association study using specific-locus amplified fragment sequencing identifies new genes influencing nitrogen use efficiency in rice landraces.

Nitrogen is essential for crop production. It is a critical macronutrient for plant growth and development. However, excessive application of nitrogen fertilizer is not only a waste of resources but also pollutes the environment. An effective approach to solving this problem is to breed rice varieties with high nitrogen use efficiency (NUE). In this study, we performed a genome-wide association study (GWAS) on 419 rice landraces using 208,993 single nucleotide polymorphisms (SNPs). With the mixed linear model (MLM) in the Tassel software, we identified 834 SNPs associated with root surface area (RSA), root length (RL), root branch number (RBN), root number (RN), plant dry weight (PDW), plant height (PH), root volume (RL), plant fresh weight (PFW), root fractal dimension (RFD), number of root nodes (NRN), and average root diameter (ARD), with a significant level of p < 2.39×10-7. In addition, we found 49 SNPs that were correlated with RL, RBN, RN, PDW, PH, PFW, RFD, and NRN using genome-wide efficient mixed-model association (GEMMA), with a significant level of p < 1×10-6. Additionally, the final results for eight traits associated with 193 significant SNPs by using multi-locus random-SNP-effect mixed linear model (mrMLM) model and 272 significant SNPs associated with 11 traits by using IIIVmrMLM. Within the linkage intervals of significantly associated SNP, we identified eight known related genes to NUE in rice, namely, OsAMT2;3, OsGS1, OsNR2, OsNPF7.4, OsPTR9, OsNRT1.1B, OsNRT2.3, and OsNRT2.2. According to the linkage disequilibrium (LD) decay value of this population, there were 75 candidate genes within the 150-kb regions upstream and downstream of the most significantly associated SNP (Chr5_29804690, Chr5_29956584, and Chr10_17540654). These candidate genes included 22 transposon genes, 25 expressed genes, and 28 putative functional genes. The expression levels of these candidate genes were measured by real-time quantitative PCR (RT-qPCR), and the expression levels of LOC_Os05g51700 and LOC_Os05g51710 in C347 were significantly lower than that in C117; the expression levels of LOC_Os05g51740, LOC_Os05g51780, LOC_Os05g51960, LOC_Os05g51970, and LOC_Os10g33210 were significantly higher in C347 than C117. Among them, LOC_Os10g33210 encodes a peptide transporter, and LOC_Os05g51690 encodes a CCT domain protein and responds to NUE in rice. This study identified new loci related to NUE in rice, providing new genetic resources for the molecular breeding of rice landraces with high NUE.

Eco-physiology and environmental impacts of newly developed rice genotypes for improved yield and nitrogen use efficiency coordinately

Significant advancements have been made in understanding the genetic regulation of nitrogen use efficiency (NUE) and identifying crucial NUE genes in rice. However, the development of rice genotypes that simultaneously exhibit high yield and NUE has lagged behind these theoretical advancements. The grain yield, NUE, and greenhouse gas (GHG) emissions of newly-bred rice genotypes under reduced nitrogen application remain largely unknown. To address this knowledge gap, field experiments were conducted, involving 80 indica (14 to 19 rice genotypes each year in Wuxue, Hubei) and 12 japonica (8 to 12 rice genotypes each year in Yangzhou, Jiangsu). Yield, NUE, agronomy, and soil parameters were assessed, and climate data were recorded. The experiments aimed to assess genotypic variations in yield and NUE among these genotypes and to investigate the eco-physiological basis and environmental impacts of coordinating high yield and high NUE. The results showed significant variations in yield and NUE among the genotypes, with 47 genotypes classified as moderate-high yield with high NUE (MHY_HNUE). These genotypes demonstrated the higher yields and NUE levels, with 9.6 t ha−1, 54.4 kg kg−1, 108.1 kg kg−1, and 64 % for yield, NUE for grain and biomass production, and N harvest index, respectively. Nitrogen uptake and tissue concentration were key drivers of the relationship between yield and NUE, particularly N uptake at heading and N concentrations in both straw and grain at maturity. Increase in pre-anthesis temperature consistently lowered yield and NUE. Genotypes within the MHY_HNUE group exhibited higher methane emissions but lower nitrous oxide emissions compared to those in the low to middle yield and NUE group, resulting in a 12.8 % reduction in the yield-scaled greenhouse gas balance. In conclusion, prioritizing crop breeding efforts on yield and resource use efficiency, as well as developing genotypes resilient to high temperatures with lower GHGs, can mitigate planetary warming.

Improving grain yield and nitrogen use efficiency of direct-seeded rice with simplified and nitrogen-reduced practices under a double-cropping system in South China.

Enhancing grain yield and nitrogen use efficiency (NUE) of rice is of great importance for sustainable agricultural development. Little effort has been made to increase grain yield and NUE of direct-seeded rice under the double-cropping system in South China. Field trials were conducted during 2018-2020 with four treatments, including nitrogen-free, farmers' fertilization practice (FP), 'three controls' nutrient management (TC), and simplified and nitrogen-reduced practice (SNRP). Grain yield under SNRP averaged 6.46 t ha-1 during the three years and was 23.0% higher than that of FP but comparable to that of TC. Recovery efficiency (REN ), agronomic efficiency (AEN ), and partial factor productivity (PFPN ) of nitrogen under SNRP increased by 12.0-22.7%, 159.3-295.0% and 94.6-112.5% respectively compared with FP. Harvest index and sink capacity increased by 7.3-10.8% and 14.9-21.3% respectively. Percentage of productive tillers (PPT) and biomass after heading increased by 24.0% and 104.5% respectively. Leaf nitrogen concentration at heading and nitrogen accumulation after heading increased by 16.3% and 842.0% respectively. Grain yield was positively correlated with PPT, sink capacity, harvest index, biomass and nitrogen accumulation after heading, REN , AEN , and PFPN . Grain yield and NUE under SNRP were superior to those under FP and comparable to those under TC. Increase in sink capacity, higher PPT, more biomass and nitrogen accumulation after heading, and greater harvest index were responsible for high grain yield and NUE in SNRP with reduced nitrogen fertilizer and labor input. SNRP is a feasible approach for direct-seeded rice under a double-cropping system in South China. © 2023 Society of Chemical Industry.