Defining the physiological determinants of low nitrogen requirement in wheat

Nitrogen (N) is a major nutrient limiting productivity in many ecosystems. The large N demands associated with food crop production are met mainly through the provision of synthetic N fertiliser, leading to economic and ecological costs. Optimising the balance between N supply and demand is key to reducing N losses to the environment. Wheat (Triticum aestivum L.) production provides food for millions of people worldwide and is highly dependent on sufficient N supply. The size of the N sink, i.e. wheat grain (number, size, and protein content) is the main driver of high N requirement. Optimal functioning of temporary sinks, in particular the canopy, can also affect N requirement. N use efficiency (i.e. yield produced per unit of N available) tends to be lower under high N conditions, suggesting that wheat plants are more efficient under low N conditions and that there is an optimal functioning yet unattained under high N conditions. Understanding the determinants of low N requirement in wheat would provide the basis for the selection of genetic material suitable for sustainable cereal production. In this review, we dissect the drivers of N requirement at the plant level along with the temporal dynamics of supply and demand.

The plant immune receptors NRG1.1 and ADR1 are calcium influx channels

Plant nucleotide-binding leucine-rich repeat receptors (NLRs) regulate immunity and cell death. RPW8 domain-containing “helper” NLRs (RNLs) are required by many “sensor” NLRs. Our crystal structure of the RNL N REQUIREMENT GENE 1.1 (NRG1.1) N-terminal signaling domain resembled that of the resting state plant resistosome-forming HOPZ-ACTIVATED RESISTANCE 1 (ZAR1) and the animal MIXED-LINEAGE KINASE-LIKE (MLKL) cation channel. Active NRG1.1 oligomerized, was enriched in plasma membrane puncta and conferred cytoplasmic Ca2+ influx in plant and human HeLa cells. NRG1.1-dependent Ca2+ influx and cell death were sensitive to Ca2+ channel blockers. Ca2+ influx and cell death mediated by NRG1.1 and ACTIVATED DISEASE RESISTANCE 1 (ADR1), another RNL, required conserved negatively charged N-terminal residues. Thus, RNLs apparently form influx channels to directly regulate cytoplasmic [Ca2+] and consequent cell death.One Sentence SummaryA specific class of plant immune receptors function as calcium-permeable channels upon activation to induce cell death.

N-terminally truncated helper NLR NRG1C antagonizes immunity mediated by its full-length neighbors NRG1A and NRG1B

Both animals and plants utilize nucleotide-binding leucine-rich repeat immune receptors (NLRs) to perceive the presence of pathogen-derived molecules and induce immune responses. NLR genes are far more abundant and diverse in higher plants. Interestingly, truncated NLRs, which lack one or more of the canonical domains, are also commonly encoded in plant genomes. However, little is known about their functions, especially regarding the N-terminally truncated ones. Here, we show that Arabidopsis thaliana (A. thaliana) N-terminally truncated helper NLR gene NRG1C (N REQUIREMENT GENE 1) is highly induced upon pathogen infection and in autoimmune mutants. The immune response and cell death conferred by some TIR (Toll/interleukin-1 receptor)-type NLRs (TNLs) are compromised in the NRG1C overexpression lines. Detailed genetic analysis revealed that NRG1C antagonizes the immunity mediated by its full-length neighbors NRG1A and NRG1B. Biochemical tests indicate that NRG1C possibly interferes with the EDS1-SAG101 complex, which likely signals together with NRG1A/1B. Interestingly, Brassicaceae NRG1Cs are functionally exchangeable, and the Nicotiana benthamiana (N. benthamiana) N-terminally truncated helper NLR NRG2 antagonizes NRG1 in tobacco. Together, our study uncovers an unexpected negative role of N-terminally truncated helper NLRs in different plants.

Investigation of the Effect of Slurry, Combined with Inorganic N Rate and Timing, on the Yield of Spring Barley Post Cover Crop of Stubble Turnips

Integration of cover crops into arable rotations over winter results in difficulty in determining the nitrogen (N) requirement for the following commercial crop. The region of Northern Ireland (NI) has had no previous field research on cover crops and how they may affect N supply to the following commercial crop. Stubble turnips (Brassica rapa oleifera L.) were sown as a cover crop, after the harvest of winter barley (Hordeum vulgare L.) and retained over winter. Prior to planting the stubble turnips, pig slurry was applied to maximise cover crop growth. The stubble turnips accumulated 111 and 150 kg N/ha in their biomass. This equates to 79 and 107% of the N requirement of a 5 t/ha spring barley crop, if this N is released sufficiently. In this experiment, the cover crop of stubble turnips was over-sown with spring barley and supplemented with different rates of organic manures (either applied at 50 m3/ha of pig slurry or not applied), and inorganic N fertiliser (0, 70 and 140 kg N/ha), at two different timings (early or late). In the two experimental years, additional N supplied in the form of inorganic N or organic manures, did not significantly enhance spring barley yields. No control area of fallow was included in this trial. However, this study demonstrates that in this region there may be a greater rate of N release from the cover crop of stubble turnips than estimated due to agronomic management practices applied and conducive climatic conditions. This means that in this study location, a reduced N rate programme supplemented to the spring barley is possible, which lead to considerable financial savings.

Crop and Residue Management Improves Productivity and Profitability of Rice–Maize System in Salt-Affected Rainfed Lowlands of East India

This study was conducted over 3 years in a salt-affected coastal rainfed lowland ecosystem. Farmers most commonly grow tall rice varieties in the wet season to cope with flash and/or stagnant floods, leading to large amounts of rice residue production. Most of the land remains fallow during the dry season because of increased salinity and scarcity of freshwater for irrigation. The study aims to provide options for increasing cropping intensity through management of crop residues (CR) and soil salinity, conservation of soil moisture, and reduction in production cost. The rice–maize rotation was assessed with rice as the main plot as (1) puddled transplanted rice (PTR) with CR of both rice and maize removed, (2) PTR and 40% CR of both crops retained, (3) dry direct-seeded rice (DSR) with CR of both crops removed, and (4) DSR with 40% CR of both crops retained. Maize in the dry season was supplied with different N levels as sub-plots—control (0 kg N ha−1), 80, 120, and 160 kg N ha−1. DSR, when combined with CR retention (DSR + R), reduced soil salinity. The increase in rice grain yield with CR retention (observed in second and third years) and crop establishment (higher in DSR versus PTR in the third year) was 16 and 24%, respectively. The cost of production increased by 17% (USD 605 ha−1) in PTR compared with DSR (USD 518 ha−1). CR retention reduced irrigation water requirement by 37% and N requirement by 40 kg ha−1 for hybrid maize. When CR was removed (−R), the N requirement for hybrid maize increased to 160 kg N ha−1 compared to when it was partially (40%) retained, where the requirement was 120 kg ha−1 with similar yields. Available N was highest under DSR + R (314 kg ha−1) and lowest under PTR − R (169 kg ha−1), and it also increased with increasing N application up to 120 kg ha−1 (+R) and 160 kg ha−1 (−R). The results of the study hold promise for increasing cropping intensity and farmers’ incomes, with broader implications for increasing productivity on about 2.95 million hectares currently under a rice–fallow system in eastern India, and in coastal areas affected by similar conditions in South and Southeast Asia.

Moderately low nitrogen application mitigate the negative effects of salt stress on annual ryegrass seedlings

Appropriate application of nitrogen (N) can alleviate the salt stress-induced damage on plants. This study explores the changes of nitrogen requirement in feeding annual ryegrass seedlings under mild salt concentrations (50 mM, 100 mM) plus its underlying mitigation mechanism. Results showed that low salt concentration decreased N requirement as observed from the increment in plant height and biomass at a relative low N level (2.0 mM not 5.0 mM). Under salt treatment, especially at 50 mM NaCl, the OJIP (Chl a fluorescence induction transient) curve and a series of performance indexes (PIABS, RC/CS0, ET0/CS0, ϕE0, ϕ0) peaked whereas DI0/RC, Vj and M0 were the lowest under moderately low N level (2.0 mM). In addition, under salt stress, moderately low N application could maintain the expression of NR (nitrate reductase) and GS (glutamine synthetase) encoding genes at a relatively stable level but had no effect on the expression of detected NRT (nitrate transporter) gene. The seedlings cultured at 2.0 mM N also exhibited the highest activity of CAT and POD antioxidant enzymes and the lowest MDA content and EL under relative low level of salt treatment. These results indicated that mild salt treatment of annual ryegrass seedlings might reduce N requirement while moderately low N application could promote their growth via regulating photosynthesis, alleviating ROS-induced (reactive oxygen species) damage and maintenance of N metabolism. These results also can provide useful reference for nitrogen application in moderation rather than in excess on annual ryegrass in mild or medium salinity areas through understanding the underlying response mechanisms.

Nitrogen fertilization recommendation for corn cultivated under no-tillage

ABSTRACT The amount of nitrogen (N) suggested for corn crop must meet its demand, maximizing yield and minimizing losses. Therefore, the objective of this study was to determine the recommendation of N fertilization for corn grown under no-tillage, using the method that considers the availability of N from the soil, the N requirement for the crop to reach the projected yield and the N-fertilizer recovery efficiency. The experiment consisted of four doses of N (0, 30, 70 and 95 kg ha-1), arranged in randomized blocks, with five repetitions. N stock of 4,357.90 kg ha-1 in the 0-20 cm soil layer provides corn plants with 52.83 kg of N ha-1, corresponding to a mineralization coefficient of 1.2%. The N-fertilizer recovery efficiency and the harvest index show a progressive linear increase according to N doses. In projections of yields lower than 1,000 kg ha-1, N fertilization is not necessary; however, in corn cultivation under no-tillage aiming at yield above 5,000 kg ha-1, fertilization needs to be performed with doses above 100 kg of N ha-1.

A Novel Method for Estimating Nitrogen Stress in Plants Using Smartphones

For profits in crop production, it is important to ensure that plants are not subjected to nitrogen stress (NS). Methods to detect NS in plants are either time-consuming (e.g., laboratory analysis) or require expensive equipment (e.g., a chlorophyll meter). In this study, a smartphone-based index was developed for detecting NS in plants. The index can be measured in real time by capturing images and processing them on a smartphone with network connectivity. The index is calculated as the ratio of blue reflectance to the combined reflectance of blue, green, and red wavelengths. Our results indicated that the index was specific to NS and decreased with increasing stress exposure in plants. Further, the index was related to photosynthesis based on the path analysis of several physiological traits. Our results further indicate that index decreased in the NS treatment due to increase in reflectance of red and green (or yellow) wavelengths, thus it is likely related to loss of chlorophyll in plants. The index response was further validated in strawberry and hydrangea plants, with contrasting plant architecture and N requirement than petunia.

Spectral sensors prove beneficial in determining nitrogen fertilizer needs of Urochloa brizantha cv. Xaraés grass in Brazil

The objective of the present work was to evaluate the use of spectral sensors to determine nitrogen fertilizer requirements for pastures of Urochloa brizantha cv. Xaraés in Brazil. The experimental design was a randomized block design with 4 replications of 4 treatments: a control treatment (TT) without application of N; a reference treatment (TR) with N applied at a standard predetermined fixed rate (150 kg urea/ha/cycle); a treatment using GreenSeekerTM (TG) to determine N requirement by the canopy normalized difference vegetation index (NDVI); and a treatment using SPAD 502 (TS) to determine N requirement by foliar chlorophyll assessment. For treatments involving spectral sensors, N fertilizer was applied at half the rate of that in the reference treatment at the beginning of each cycle and further N was applied only when the nitrogen sufficiency index dropped below 0.85. The sensors used in the work indicated that no additional N fertilizer was required by these pastures above the half rates applied. Applying N at the reduced rates to the pastures was more efficient than the pre-determined fixed rate, as both sensor treatments and the fixed rate treatment produced similar total forage yields, with similar crude protein concentrations. All fertilized pastures supported similar stocking rates, while the sensor treatments used less N fertilizer, i.e. 75 kg urea/ha/cycle less than the reference plot. Longer-term studies to verify these findings are warranted followed by promotion of the technology to farmers to possibly reduce fertilizer application rates, improve profitability and provide environmental benefits.

Dynamic changes and genotypic variations of nitrogen concentration and remobilization for 20 tea plant (Camellia sinensis) cultivars throughout growing seasons

Background: Tea plant ( Camellia sinensis ) is an evergreen perennial plant and characterized by a high nitrogen (N) requirement. There are roundly bud sprouting and leaves development for plucking and pruning annually, leading to continuous and substantial amount of N removal. Appropriate level of N application is closely related with high yield and top quality, therefore understanding the underlying mechanism is very crucial for development of optimized tea garden management practices according to genotypes’ requirement. Results: This study aimed to assess variation for dynamic N concentration, N remobilization efficiency (NRE) and N utilization efficiency (NUtE) changes during growing seasons among 20 tea plant cultivars at sufficient N level. The average N concentration varied between 31.05 and 44.2 g kg -1 in one bud with two leaves, between 22.67 and 29.42 g kg -1 in leaves attached to green-red stems, between 20.79 and 24.57 g kg -1 respectively. The dynamic changes of N concentration represented different profiles of ‘S’, ‘U’ and ‘S-like’-shape respectively. Specific NRE defined here is dependent on the development rounds and accompanied with N fluxes between leaves compartments. Nevertheless, the rates and order of N remobilization were inconsistent among genotypes during the entire growing seasons, which might be affected by the amount of N requirement and managed at whole plant level. The dynamic changes of average NUtE among cultivars followed an ‘S’-shape. NUtE addressed here was special for harvestable part and lower NUtE is highly associated with tea quality. Conclusions: The result revealed the annual growing rhythm and physiological character related with N indices, which was related with the amount and optimal time for N fertilization requirement dependent on tea plant genotype. An optimized NUtE should be optimized by combination of tea garden management and breeding practices to achieve economic benefit, N use efficiency and sustainable development.