Engineering nitrogen use efficient crop plants: the current status

In the last 40 years the amount of synthetic nitrogen (N) applied to crops has risen drastically, resulting in significant increases in yield but with considerable impacts on the environment. A requirement for crops that require decreased N fertilizer levels has been recognized in the call for a ‘Second Green Revolution’ and research in the field of nitrogen use efficiency (NUE) has continued to grow. This has prompted a search to identify genes that improve the NUE of crop plants, with candidate NUE genes existing in pathways relating to N uptake, assimilation, amino acid biosynthesis, C/N storage and metabolism, signalling and regulation of N metabolism and translocation, remobilization and senescence. Herein is a review of the approaches taken to determine possible NUE candidate genes, an overview of experimental study of these genes as effectors of NUE in both cereal and non‐cereal plants and the processes of commercialization of enhanced NUE crop plants. Patents issued regarding increased NUE in plants as well as gene pyramiding studies are also discussed as well as future directions of NUE research.     

Optimising non-destructive sampling methods to study nitrogen use efficiency throughout the growth-cycle of giant C4 crops

Plant and Soil - The improvement of nitrogen use efficiency (NUE) of crops allows crop nitrogen (N) demands to be met while reducing N supply, and so reducing excess N which has potential negative...     

Cereal area and nitrogen use efficiency are drivers of future nitrogen fertilizer consumption

At a global scale, cereal yields and fertilizer N consumption have increased in a near-linear fashion during the past 40 years and are highly correlated with one another. However,large differences exist in historical trends of N fertilizer usage and nitrogen use efficiency (NUE)among regions, countries, and crops. The reasons for these differences must be understood to estimate future N fertilizer requirements. Global nitrogen needs will depend on: (i) changes in cropped cereal area and the associated yield increases required to meet increasing cereal demand from population and income growth, and (ii) changes in NUE at the farm level. Our analysis indicates that the anticipated 38% increase in global cereal demand by 2025 can be met by a 30% increase in N use on cereals, provided that the steady decline in cereal harvest area is halted and the yield response to applied N can be increased by 20%. If losses of cereal cropping area continue at the rate of the past 20 years (-0.33% per year) and NUE cannot be increased substantially, a 60% increase in global N use on cereals would be required to meet cereal demand. Interventions to increase NUE and reduce N losses to the environment must be accomplished at the farm- or field-scale through a combination of improved technologies and carefully crafted local policies that contribute to the adoption of improved N management; uniform regional or national directives are unlikey to be effective at both sustaining yield increases and improving NUE. Examples from several countries show that increases in NUE at rates of 1% per year or more can be achieved if adequate investments are made in research and extension. Failure to arrest the decrease in cereal crop area and to improve NUE in the world's most important agricultural systems will likely cause severe damage to environmental services at local, regional, and global scales due to a large increase in reactive N load in the environment.     

Cereal area and nitrogen use efficiency are drivers of future nitrogen fertilizer consumption

At a global scale, cereal yields and fertilizer N consumption have increased in a near-linear fashion during the past 40 years and are highly correlated with one another. However, large differences exist in historical trends of N fertilizer usage and nitrogen use efficiency (NUE) among regions, countries, and crops. The reasons for these differences must be understood to estimate future N fertilizer requirements. Global nitrogen needs will depend on: (i) changes in cropped cereal area and the associated yield increases required to meet increasing cereal demand from population and income growth, and (ii) changes in NUE at the farm level. Our analysis indicates that the anticipated 38% increase in global cereal demand by 2025 can be met by a 30% increase in N use on cereals, provided that the steady decline in cereal harvest area is halted and the yield response to applied N can be increased by 20%. If losses of cereal cropping area continue at the rate of the past 20 years (-0.33% per year) and NUE cannot be increased substantially, a 60% increase in global N use on cereals would be required to meet cereal demand. Interventions to increase NUE and reduce N losses to the environment must be accomplished at the farm- or field-scale through a combination of improved technologies and carefully crafted local policies that contribute to the adoption of improved N management; uniform regional or national directives are unlikey to be effective at both sustaining yield increases and improving NUE. Examples from several countries show that increases in NUE at rates of 1% per year or more can be achieved if adequate investments are made in research and extension. Failure to arrest the decrease in cereal crop area and to improve NUE in the world's most important agricultural systems will likely cause severe damage to environmental services at local, regional, and global scales due to a large increase in reactive N load in the environment.     

Cereal area and nitrogen use efficiency are drivers of future nitrogen fertilizer consumption

At a global scale, cereal yields and fertilizer N consumption have increased in a near-linear fashion during the past 40 years and are highly correlated with one another. However, large differences exist in historical trends of N fertilizer usage and nitrogen use efficiency (NUE) among regions, countries, and crops. The reasons for these differences must be understood to estimate future N fertilizer requirements. Global nitrogen needs will depend on: (i) changes in cropped cereal area and the associated yield increases required to meet increasing cereal demand from population and income growth, and (ii) changes in NUE at the farm level. Our analysis indicates that the anticipated 38% increase in global cereal demand by 2025 can be met by a 30% increase in N use on cereals, provided that the steady decline in cereal harvest area is halted and the yield response to applied N can be increased by 20%. If losses of cereal cropping area continue at the rate of the past 20 years (?0.33% per year) and NUE cannot be increased substantially, a 60% increase in global N use on cereals would be required to meet cereal demand. Interventions to increase NUE and reduce N losses to the environment must be accomplished at the farm-or field-scale through a combination of improved technologies and carefully crafted local policies that contribute to the adoption of improved N management; uniform regional or national directives are unlikey to be effective at both sustaining yield increases and improving NUE. Examples from several countries show that increases in NUE at rates of 1% per year or more can be achieved if adequate investments are made in research and extension. Failure to arrest the decrease in cereal crop area and to improve NUE in the world’s most important agricultural systems will likely cause severe damage to environmental services at local, regional, and global scales due to a large increase in reactive N load in the environment.     

Nitrogen assimilation in plants: current status and future prospects

Nitrogen(N) is the driving force for crop yields; however, excessive N application in agriculture not only increases production cost, but also causes severe environmental problems. Therefore, comprehensively understanding the molecular mechanisms of N use efficiency(NUE) and breeding crops with higher NUE is essential to tackle these problems. NUE of crops is determined by N uptake, transport, assimilation, and remobilization. In the process of N assimilation, nitrate reductase(NR), nitrite redu...     

Variation in the use efficiency of N under moderate water deficit in tomato plants (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis>) differing in their tolerance to drought

Nitrogen-use efficiency (NUE) is one of the determining factors in crop productivity. However, the accumulation and use of this nutrient can be affected by several elements, including the species or cultivar and the water supply. Currently, one agricultural priority is to improve NUE together with greater water-deficit tolerance of crops in Mediterranean environments in order to reduce the application of nitrogenous fertilizers and boost production. The aim of the present study was to evaluate the response of different tomato-plant genotypes in relation to NUE under water stress conditions and optimal nitrogen condition. The water deficit provoked a decline in the concentration and uptake of N in all the cultivars except in cv. Zarina, which improved its NUE under these conditions. In turn, it was this cultivar which underwent the strongest relative growth during water stress together with the greatest leaf relative-water content, which could be associated with improved NUE.     

Can less yield more? Is reducing nutrient input into the environment compatible with maintaining crop production?

Plant scientists have long recognized the need to develop crops that absorb and use nutrients more efficiently. Two approaches have been used to increase nutrient use efficiency (NUE) in crop plants. The first involves both traditional breeding and marker-assisted selection in an attempt to identify the genes involved. The second uses novel gene constructs designed to improve specific aspects of NUE. Here, we discuss some recent developments in the genetic manipulation of NUE in crop plants and argue that an improved understanding of the transition between nitrogen assimilation and nitrogen recycling will be important in applying this technology to increasing crop yields. Moreover, we emphasize the need to combine genetic and transgenic approaches to make significant improvements in NUE.     

农田水氮关系及其协同管理

作物施氮反应及其氮肥利用率不仅取决于氮肥管理,还与水资源管理有关,并且受到地区气候因素的影响。针对中国灌溉农区氮肥环境污染问题日益突出,协调农田水氮管理,如通过改善水资源管理,发挥水氮协同效应,以提高水分利用效率来改善氮肥利用率,实现水氮利用率双赢,是当前农业水氮管理中亟待探讨和回答的问题。通过对农田水氮协同相关研究文献资料的综述,以华北平原集约种植体系水氮管理为例,根据历年统计数据,分析了该区年水热条件下粮食产量与水、氮及水氮利用效率之间的关系。研究表明,水和氮与作物产量在一定范围表现为水氮的协同效应。水分利用效率一般随灌溉水量减少及氮肥用量增加而提高;氮肥利用效率随氮用量增加而下降。适量节水和减氮分别有助水分利用效率和氮肥利用效率的改善。在气候变暖、变干条件下,适量施氮成为改善水氮利用效率的关键对策。     

The vegetative nitrogen response of sorghum lines containing different alleles for nitrate reductase and glutamate synthase

Improving the nitrogen (N) responsiveness of crops is crucial for food security and environmental sustainability, and breeding N use efficient (NUE) crops has to exploit genetic variation for this complex trait. We used reverse genetics to examine allelic variation in two N metabolism genes. In silico analysis of the genomes of 44 genetically diverse sorghum genotypes identified a nitrate reductase and a glutamate synthase gene that were under balancing selection in improved sorghum cultivars. We hypothesised that these genes are a potential source of differences in NUE, and selected parents and progeny of nested association mapping populations with different allelic combinations for these genes. Allelic variation was sourced from African (Macia) and Indian (ICSV754) genotypes that had been incorporated into the Australian elite parent R931945-2-2. Nine genotypes were grown for 30 days in a glasshouse and supplied with continuous limiting or replete N, or replete N for 27 days followed by 3 days of N starvation. Biomass, total N and nitrate contents were quantified together with gene expressions in leaves, stems and roots. Limiting N supply universally resulted in less shoot and root growth, increased root weight ratio and reduced tissue nitrate and total N concentrations. None of the tested genotypes exceeded growth or NUE of the elite parent R931945-2-2 indicating that the allelic combinations did not confer an advantage during early vegetative growth. Thus, the next steps for ascertaining potential effects on NUE include growing plants to maturity. We conclude that reverse genetics that take advantage of rapidly expanding genomic databases enable a systematic approach for developing N-efficient crops.     

Nitrogen use efficiency. 1. Uptake of nitrogen from the soil

The nitrogen use efficiency (NUE) of crop plants can be expressed very simply as the yield of nitrogen per unit of available nitrogen in the soil. This NUE can be divided into two processes: uptake efficiency, the ability of the plant to remove N from the soil normally present as nitrate or ammonium ions, and the utilisation efficiency, the ability of the plant to transfer the N to the grain, predominantly present as protein. In this article, we have highlighted the latest developments in the isolation and characterisation of the genes involved in the uptake of nitrogen from the soil.     

Agronomic improvements through the genetic and physiological regulation of nitrogen uptake in wheat (Triticum aestivum L.)

Nitrogen (N) uptake is the first step in nitrate assimilation, and efficient N uptake is essential for plant growth, especially for protein biosynthesis and photosynthetic activities. In cereals, improved N uptake is closely coupled with an increase in nitrogen use efficiency (NUE) and yield improvements. Because wheat (Triticum aestivum L.) is a leading crop worldwide, a better understanding of N uptake regulation in wheat is vital to improving NUE and developing sustainable agricultural systems. However, detailed information regarding the biological mechanisms that are responsible for the more efficient uptake of ambient N by wheat is limited. This review presents recent developments in the biological mechanisms of N uptake in wheat, including plant growth regulations, fundamental roles of root systems, interactions between N species, and genetic controls. Specifically, this paper provides a number of potential strategies that can be used to increase wheat N uptake. The information provided here may guide N fertilizer management during wheat production and further elucidate the plant regulatory mechanisms that are involved in N uptake, which can thereby increase wheat NUE.     

C3和C4植物的氮素利用机制

提高植物的氮素利用效率(NUE)不仅有利于保障全球粮食安全, 也是实现农业可持续发展的重要途径。近半个世纪以来, 植物氮素利用机理研究已取得重要进展, 但NUE的调控机制仍不明确, NUE的提高仍然十分有限。高等植物集光合碳素同化和氮素同化于一体, 只有碳氮代谢相互协调, 才能维持植物体内的碳氮平衡, 保证植物正常生长发育。由于C₃和C₄植物的光合氮素利用率(PNUE)存在差异, 对氮素的利用效率也会存在差异。为了更有效地提高作物的NUE, 须更全面地了解C₃和C₄植物对氮素吸收、转运、同化和信号转导等关键因子的功能和调控机制。此外, 面对大气CO₂浓度增高和全球气候变暖条件下的植物碳氮同化及其机理的研究也不容忽视。该文综述了C₃和C₄植物氮素利用关键因素的差异及其调控机制, 并对提高C₃禾本科作物氮素利用效率的遗传改良途径进行了展望。     

Plant nitrogen availability and crosstalk with phytohormones signallings and their biotechnology breeding application in crops

Nitrogen (N), one of the most important nutrients, limits plant growth and crop yields in sustainable agriculture system, in which phytohormones are known to play essential roles in N availability. Hence, it is not surprising that massive studies about the crosstalk between N and phytohormones have been constantly emerging. In this review, with the intellectual landscape of N and phytohormones crosstalk provided by the bibliometric analysis, we trace the research story of best-known crosstalk between N and various phytohormones over the last 20 years. Then, we discuss how N regulates various phytohormones biosynthesis and transport in plants. In reverse, we also summarize how phytohormones signallings modulate root system architecture (RSA) in response to N availability. Besides, we expand to outline how phytohormones signallings regulate uptake, transport, and assimilation of N in plants. Further, we conclude advanced biotechnology strategies, explain their application, and provide potential phytohormones-regulated N use efficiency (NUE) targets in crops. Collectively, this review provides not only a better understanding on the recent progress of crosstalk between N and phytohormones, but also targeted strategies for improvement of NUE to increase crop yields in future biotechnology breeding of crops.     

Genetic variation in eggplant for Nitrogen Use Efficiency under contrasting NO3‐ supply

Eggplant (Solanum melongena L.) yield is highly sensitive to N fertilization, the excessive use of which is responsible for environmental and human health damage. Lowering N input together with the selection of improved Nitrogen‐Use‐Efficiency (NUE) genotypes, more able to uptake, utilize, and remobilize N available in soils, can be challenging to maintain high crop yields in a sustainable agriculture. The aim of this study was to explore the natural variation among eggplant accessions from different origins, in response to Low (LN) and High (HN) Nitrate (NO₃^‐) supply, to identify NUE‐contrasting genotypes and their NUE‐related traits, in hydroponic and greenhouse pot experiments. Two eggplants, AM222 and AM22, were identified as N‐use efficient and inefficient, respectively, in hydroponic, and these results were confirmed in a pot experiment, when crop yield was also evaluated. Overall, our results indicated the key role of N‐utilization component (NUtE) to confer high NUE. The remobilization of N from leaves to fruits may be a strategy to enhance NUtE, suggesting glutamate synthase as a key enzyme. Further, omics technologies will be used for focusing on C‐N metabolism interacting networks. The availability of RILs from two other selected NUE‐contrasting genotypes will allow us to detect major genes/quantitative trait loci related to NUE.     

Dynamic responses of nitrous oxide emission and nitrogen use efficiency to nitrogen and biochar amendment in an intensified vegetable field in southeastern China

Intensive vegetable production exhibits contrasting characteristics of high nitrous oxide (N₂O) emissions and low nitrogen use efficiency (NUE). In an effort to mitigate N₂O emissions and improve NUE, a field experiment with nine consecutive vegetable crops was designed to study the combined effects of nitrogen (N) and biochar amendment and their interaction on soil properties, N₂O emission and NUE in an intensified vegetable field in southeastern China. We found that N application significantly increased N₂O emissions, N₂O–N emission factors and yield‐scaled N₂O emissions by 51–159%, 9–125% and 14–131%, respectively. Moreover, high N input significantly decreased N partial factor productivity (PFPN) and even yield during the seventh to ninth vegetable crops along with obvious soil degradation and mineral N accumulation. To the contrary, biochar amendment resulted in significant decreases in cumulative N₂O emissions, N₂O–N emission factor and yield‐scaled N₂O emissions by 5–39%, 16–67% and 14–53%, respectively. In addition, biochar significantly increased yield, PFPN and apparent recovery of N (ARN). Although without obvious influence during the first to fourth vegetable crops, biochar amendment mitigated N₂O emissions during the fifth to ninth vegetable crops. The relative effects of biochar amendments were reduced with increasing N application rate. Hence, while high N input produced adverse consequences such as mineral N accumulation and soil degradation in the vegetable field, biochar amendment can be a beneficial agricultural strategy to mitigate N₂O emissions and improve NUE and soil quality in vegetable field.     

藜个体在高密度种群中的氮素利用效率

 氮素利用效率（NUE）是植物养分策略研究中的一项重要内容。该文利用Berendse和Aerts提出的氮素利用效率概念和原理研究了高密度的藜(Chenopodium album)种群中不同植物个体在种内竞争条件下的氮素利用效率。结果表明,由于植株的氮素吸收速率与其个体大小成非线性关系,说明不同植株个体对氮素的竞争属于非对称竞争。个体较大的植株氮素输入较高,而个体较小的植株氮素输出较高,因而较大个体植株的氮素净增加也较高。植株的氮素损失随着个体大小的增加而增加,较大植株个体的氮素浓度随着生长而下降,而较小植株个体的氮素浓度随时间的变化不大,说明个体较小的植株的生长受光照的限制比受氮素的限制更大,而对较大的植株个体而言,它们的生长受氮素的限制更大。高密度藜种群中的不同植物个体具有不同的养分策略,氮素利用效率及其组成部分氮素生产力（NP）和氮素滞留时间（MRT）均不同。植株的NP和MRT与其个体大小正相关,较大的植物个体具有较高的NP和较长的MRT,因而氮素利用效率也高于个体较小的植株。在个体水平上,种内不同植株的NP与MRT不存在权衡关系（Trade-off）。因此,Berendse和Aerts提出的氮素利用效率概念不仅适用于研究种间的养分策略,对于研究种内不同植株的养分策略也同样适用。