low-N Treatment Research Articles

Nitrogen modulates the ozone response of Mediterranean wheat: Considerations for ozone risk assessment

The experiment was conducted in an Open Top Chamber facility located in the Mediterranean basin to investigate how nitrogen (N) fertilization affects the response of wheat to ozone (O3) exposure. The study considered the response of Artur Nick, a modern wheat cultivar commonly used in the area, to three O3 exposure levels (ambient and elevated ambient, +20 and +40 nL L−1 O3), and two N fertilization doses (100 and 200 kg ha−1). Measurements included leaf gas exchange, leaf chlorophyll content, leaf and grain N content, plant growth and yield parameters. Ozone × N interactive effects were studied and quantified based on accumulated O3 concentrations above a 40 nL L−1 threshold (AOT40) and phytotoxic O3 dose (POD) indices, which are used in O3-risk assessments, from which critical levels (CL) for a 5 % effect were derived.Results revealed that O3 impacts on growth and yield parameters were stronger under the highest N fertilization dose. In consequence, O3 Critical Levels (CL) were as much as 3–4 times lower for grain yield in the high-N compared to the low-N treatment. Interestingly, O3 limited the fertilizer stimulus, strongly reducing the N use efficiency for grain yield and the agronomic efficiency of N for protein yield. Another important aspect was that 71 % of the POD was accumulated before anthesis, stressing the potential importance of O3 exposure during the vegetative phase of wheat under Mediterranean conditions, which is usually considered less important than post-anthesis exposure.In conclusion, this study suggests the need to consider crop N management in the derivation of O3 CLs, due to its effect on dose-response relationships used for CL derivation, including the potential O3 effects in N use efficiency. Therefore, N modulation could be considered in the O3-risk assessment methodology to be applied in risk exercises when negotiating air pollution abatement policies.

MicroRNAs Participate in Morphological Acclimation of Sugar Beet Roots to Nitrogen Deficiency.

Nitrogen (N) is essential for sugar beet (Beta vulgaris L.), a highly N-demanding sugar crop. This study investigated the morphological, subcellular, and microRNA-regulated responses of sugar beet roots to low N (LN) stress (0.5 mmol/L N) to better understand the N perception, uptake, and utilization in this species. The results showed that LN led to decreased dry weight of roots, N accumulation, and N dry matter production efficiency, along with damage to cell walls and membranes and a reduction in organelle numbers (particularly mitochondria). Meanwhile, there was an increase in root length (7.2%) and branch numbers (29.2%) and a decrease in root surface area (6.14%) and root volume (6.23%) in sugar beet after 7 d of LN exposure compared to the control (5 mmol/L N). Transcriptomics analysis was confirmed by qRT-PCR for 6 randomly selected microRNAs, and we identified 22 differentially expressed microRNAs (DEMs) in beet root under LN treatment. They were primarily enriched in functions related to binding (1125), ion binding (641), intracellular (437) and intracellular parts (428), and organelles (350) and associated with starch and sucrose metabolism, tyrosine metabolism, pyrimidine metabolism, amino sugar and nucleotide sugar metabolism, and isoquinoline alkaloid biosynthesis, as indicated by the GO and KEGG analyses. Among them, the upregulated miR156a, with conserved sequences, was identified as a key DEM that potentially targets and regulates squamosa promoter-binding-like proteins (SPLs, 104889216 and 104897537) through the microRNA-mRNA network. Overexpression of miR156a (MIR) promoted root growth in transgenic Arabidopsis, increasing the length, surface area, and volume. In contrast, silencing miR156a (STTM) had the opposite effect. Notably, the fresh root weight decreased by 45.6% in STTM lines, while it increased by 27.4% in MIR lines, compared to the wild type (WT). It can be inferred that microRNAs, especially miR156, play crucial roles in sugar beet root's development and acclimation to LN conditions. They likely facilitate active responses to N deficiency through network regulation, enabling beet roots to take up nutrients from the environment and sustain their vital life processes.

Physiological and Transcriptional Characteristics of Banana Seedlings in Response to Nitrogen Deficiency Stress

Nitrogen is a crucial element for the growth and development of plants, directly affecting crop growth and yield. To investigate the physiological and molecular mechanism of nitrogen-deficiency stress, we conducted an investigation into the effects of different nitrogen levels on the growth, photosynthetic characteristics, and gene transcription levels of banana seedlings. Compared with the control group with normal nitrogen levels (NN), the height of plants receiving Reduced-N (NR), Low-N (LN), and N-Free (NF) treatments was decreased by 0.45 cm, 2.5 cm, and 3.25 cm, respectively. Their dry weight was reduced by 1.63 g, 2.99 g, and 2.88 g, respectively. Conversely, the dry weight of the underground plant part in the LN and NF treatment groups exhibited an increase of 0.13 g and 0.16 g, respectively. Regarding photosynthetic characteristics, the Specialty Products Agricultural Division (SPAD) values of the NR, LN, and NF treatments showed reductions of 15.5%, 30.4%, and 35.9%, respectively, compared with those of the control treatments. The values of maximum photosynthetic efficiency (Fv/Fm), actual photosynthetic efficiency (Y(Ⅱ)), and relative electron transfer (ETR) of the banana seedlings decreased to different degrees after NR, LN, and NF treatment, and their values were positively correlated with N levels. Gene transcription analysis showed that N transport-related proteins, including NRT1.7, NRT2.3a, NRT2.3b, and NRT2.5, were significantly up-regulated to increase the nitrogen absorption capacity of plant roots. On the other hand, various transcription factors including GRAS, MYB, and WRKY were notably up-regulated, facilitating root growth and the expanding root absorption area, thereby enhancing nitrogen uptake. Furthermore, genes associated with endogenous hormone metabolic pathways such as gibberellin (GA), strigolactone (SL), and brassinosteroids (BR) were activated in banana plants subjected to low nitrogen stress, enhancing the plant’s ability to adapt to nitrogen-deficient conditions. These findings offer valuable insights into understanding the transcriptional regulatory mechanisms governing banana responses to low nitrogen stress and breeding new varieties with improved nutrient utilization.

Integrated Transcriptomic and Proteomic Analyses of Low-Nitrogen-Stress Tolerance and Function Analysis of ZmGST42 Gene in Maize.

Maize (Zea mays L.) is one of the major staple crops providing human food, animal feed, and raw material support for biofuel production. For its growth and development, maize requires essential macronutrients. In particular, nitrogen (N) plays an important role in determining the final yield and quality of a maize crop. However, the excessive application of N fertilizer is causing serious pollution of land area and water bodies. Therefore, cultivating high-yield and low-N-tolerant maize varieties is crucial for minimizing the nitrate pollution of land and water bodies. Here, based on the analysis of the maize leaf transcriptome and proteome at the grain filling stage, we identified 3957 differentially expressed genes (DEGs) and 329 differentially abundant proteins (DAPs) from the two maize hybrids contrasting in N stress tolerance (low-N-tolerant XY335 and low-N-sensitive HN138) and screened four sets of low-N-responsive genes and proteins through Venn diagram analysis. We identified 761 DEGs (253 up- and 508 down-regulated) specific to XY335, whereas 259 DEGs (198 up- and 61 down-regulated) were specific to HN138, and 59 DEGs (41 up- and 18 down-regulated) were shared between the two cultivars under low-N-stress conditions. Meanwhile, among the low-N-responsive DAPs, thirty were unique to XY335, thirty were specific to HN138, and three DAPs were shared between the two cultivars under low-N treatment. Key among those genes/proteins were leucine-rich repeat protein, DEAD-box ATP-dependent RNA helicase family proteins, copper transport protein, and photosynthesis-related proteins. These genes/proteins were involved in the MAPK signaling pathway, regulating membrane lipid peroxidation, and photosynthesis. Our results may suggest that XY335 better tolerates low-N stress than HN138, possibly through robust low-N-stress sensing and signaling, amplified protein phosphorylation and stress response, and increased photosynthesis efficiency, as well as the down-regulation of 'lavish' or redundant proteins to minimize N demand. Additionally, we screened glutathione transferase 42 (ZmGST42) and performed physiological and biochemical characterizations of the wild-type (B73) and gst42 mutant at the seedling stage. Resultantly, the wild-type exhibited stronger tolerance to low N than the mutant line. Our findings provide a better understanding of the molecular mechanisms underlying low-N tolerance during the maize grain filling stage and reveal key candidate genes for low-N-tolerance breeding in maize.

Integrated physiological, transcriptomic, and metabolomic analyses reveal that low-nitrogen conditions improve the accumulation of flavonoids in snow chrysanthemum

Nitrogen (N) levels have significant effects on plant growth and chemical composition. Previous studies found that low-N treatment maintained the number of inflorescences and promoted flavonoid accumulation in snow chrysanthemum, but the underlying mechanism was not clear. To investigate the complex flavonoid biosynthesis pathway of snow chrysanthemum under low-N conditions, we compared low-N and normal-N groups across the four harvest stages. Low-N treatment caused early flowering in snow chrysanthemum and maintained the production of flowers. Low-N stress increased the carbon (C)/N ratio in flowers, thus significantly increasing the total flavonoid content in the flower bud stage, early flowering stage and full flowering stage. Moreover, analysis of the flavonoid metabolome showed that low-N treatment resulted in increased levels of kaempferol-3-O-(6''-p-coumaroyl)galactoside, quercetin-3-O-(2''-acetyl)glucuronide, 3,7-dimethylquercetagetin-(3′,4′,5,6-tetrahydroxy-3,7-dime-thoxyflavone), isotamarixin, apigenin-8-C-arabinoside, quercetin-5-O-glucuronide, and cyanidin-3-O-(6''-O-p-coumaroyl)glucoside, which further enhanced antioxidant activity. Combined flavonoid metabolism and transcriptomic data analysis indicated that PAL, 4CL, HCT, C3'H, CHS, DFR and ANR are key genes leading to the accumulation of flavonoids in snow chrysanthemum under low-N conditions. In addition, 6 transcription factors (especially MYB26c, Cluster-16181.96870) and 17 other regulators (mainly including transporter proteins) under low-N conditions are also involved in the regulation of flavonoid accumulation. This research provides a new perspective for studying the regulatory effect of N levels on the growth and flavonoid biosynthesis in snow chrysanthemum. Data availability statementThe data presented in this study are available in the article and supplementary materials.

Phosphorus Accumulation in Extracellular Polymeric Substances (EPS) of Colony-Forming Cyanobacteria Challenges Imbalanced Nutrient Reduction Strategies in Eutrophic Lakes.

Extracellular polymeric substances (EPS) are crucial for cyanobacterial proliferation; however, certain queries, including how EPS affects cellular nutrient processes and what are the implications for nutrient management in lakes, are not well documented. Here, the dynamics of cyanobacterial EPS-associated phosphorus (EPS-P) were examined both in a shallow eutrophic lake (Lake Taihu, China) and in laboratory experiments with respect to nitrogen (N) and phosphorus (P) availability. Results indicated that 40-65% of the total cyanobacterial aggregate/particulate P presented as EPS-P (mainly labile P and Fe/Al-P). Phosphorus-starved cyanobacteria rapidly replenished their EPS-P pools after the P was resupplied, and the P concentration in this pool was stable for long afterward, although the environmental P concentration decreased dramatically. A low-N treatment enhanced the EPS production alongside two-fold EPS-P accumulation (particularly labile P) higher than the control. Such patterns occurred in the lake where EPS and EPS-P contents were high under N limitation. EPS-P enrichment increased the P content in cyanobacteria; subsequently, it could hold the total P concentration higher for longer and make bloom mitigation harder. The findings outline a new insight into EPS functions in the P process of cyanobacterial aggregates and encourage consideration of both N and P reductions in nutrient management.

Differential response of rice genotypes to nitrogen availability is associated with the altered nitrogen metabolism and ionomic balance

Nitrogen (N) uptake and its assimilation are crucial steps for plant growth and productivity. Plant's N balance largely depends on nitrate (NO 3 - ) and ammonium (NH 4 + ) forms present in the rhizosphere. Due to the fluctuating and heterogeneous availability of these N forms in the soils, plants encounter low to N deficiency. In contrast to low nitrogen, high N in the form of ammonium (NH 4 + ) severely hampers plant development and causes NH 4 + toxicity. In this study, we assessed eleven rice genotypes under sufficient (SN) and low N (LN) conditions. From the analysis, we identified a rice genotype, PB1, which is hypersensitive to SN and showed reduced root and shoot growth. In contrast to the SN condition, PB1 showed improved growth performance under the LN condition. Our data show that compromised growth of PB1 under SN condition is associated with increased activity of N responsive genes such as OsAMT1.1 , OsAMT2.3 , OsAMT3.1 and OsAMT3.2 , OsNRT1.1A and OsNRT1.1B . Strikingly, LN treatment improved the root and shoot biomass with a concomitant increase in levels of NO 3 - and NH 4 + transporter genes along with an increase in shoot: root NO 3 - ratio. Additionally, we show that increased levels of N in PB1 under SN condition are associated with the enhanced activity of the GS-GOGAT pathway. Further, our ionomic analysis highlighted the role of N-defined Fe accumulation which is partially associated with the N toxicity. Taken together, our study led to identifying a rice genotype ( Oryza sativa L.) which is associated with enhanced N levels and assimilation and could be used for raising N use efficient rice varieties using breeding approaches. • Screening of rice genotypes under high and low nitrogen (N) conditions led to identify a nitrogen-sensitive rice genotype. • Optimal N sensitive genotype, PB1 shows N toxicity and improved growth under LN condition. • N toxicity under optimal or high N supply is associated with altered growth physiology and N metabolism in PB1. • Increased N metabolism is associated with altered ionomic balance.

Genome-Wide Association Studies of Maize Seedling Root Traits under Different Nitrogen Levels.

Nitrogen (N) is one of the important factors affecting maize root morphological construction and growth development. An association panel of 124 maize inbred lines was evaluated for root and shoot growth at seedling stage under normal N (CK) and low N (LN) treatments, using the paper culture method. Twenty traits were measured, including three shoot traits and seventeen root traits, a genome-wide association study (GWAS) was performed using the Bayesian-information and Linkage-disequilibrium Iteratively Nested Keyway (BLINK) methods. The results showed that LN condition promoted the growth of the maize roots, and normal N promoted the growth of the shoots. A total of 185 significant SNPs were identified, including 27 SNPs for shoot traits and 158 SNPs for root traits. Four important candidate genes were identified. Under LN conditions, the candidate gene Zm00001d004123 was significantly correlated with the number of crown roots, Zm00001d025554 was correlated with plant height. Under CK conditions, the candidate gene Zm00001d051083 was correlated with the length and area of seminal roots, Zm00001d050798 was correlated with the total root length. The four candidate genes all responded to the LN treatment. The research results provide genetic resources for the genetic improvement of maize root traits.

Low Nitrogen Enhances Apoplastic Phloem Loading and Improves the Translocation of Photoassimilates in Rice Leaves and Stems.

The grain filling of rice depends on photoassimilates from leaves and stems. Phloem loading is the first crucial step for the transportation of sucrose to grains. However, phloem loading mechanisms in rice leaves and stems and their response to nitrogen (N) remain unclear. Here, using a combination of electron microscopy, transportation of a phloem tracer and 13C labeling, phloem loading was studied in rice leaves and stems. The results showed that the sieve element-companion cell complex lacked a symplastic connection with surrounding parenchyma cells in leaves and stems. The genes expression and protein levels of sucrose transporter (SUTs) and sugars will eventually be exported transporters (SWEETs) were detected in the vascular bundle of leaves and stems. A decrease in the 13C isotope remobilization from leaves to stems and panicles following treatment with p-chloromercuribenzenesulfonic acid indicated that rice leaves and stems actively transport sucrose into the phloem. Under low-N (LN) treatment, the activities of α-amylase, β-amylase and sucrose phosphate synthase (SPS) in stems and activity of SPS in leaves increased; genes expression and protein levels of SUTs and SWEETs in leaves and stems increased; the 13C isotope reallocation in panicles increased. These indicated that LN enhanced apoplastic phloem loading in stems and leaves. This improved the translocation of photoassimilates and consequently increased grain filling percentage, grain weight and harvest index. This study provides evidence that rice leaves and stems utilize an apoplastic loading strategy and respond to N stimuli by regulating the genes expression and protein levels of SUTs and SWEETs.

Genetic improvement analysis of nitrogen uptake, utilization, translocation, and distribution in Chinese wheat in Henan Province

Genetic improvement analysis of the nitrogen use efficiency (NUE) of wheat ( Tritium aestivum L.) was undertaken to determine the factors guiding NUE in order to develop new wheat cultivars with high yield, high NUE and high quality. To investigate the genetic improvement of wheat NUE and its components, 31 wheat cultivars that had been widely planted in Henan Province since 1941 were grown under high N treatment (HN) and low N treatment (LN). The results indicated that grain yield and NUE have increased significantly with cultivar development since 1941, with an annual genetic gain of 1.03% and 0.74%, respectively, under HN and LN. The significant increase in NUE mainly resulted from a significant increase in N uptake efficiency (NupE) and N utilization efficiency (NutE). NutE was the predominant component contributing to NUE under HN, while NupE was more important than NutE for NUE under LN. The improvement of NutE occurred at the expense of lower grain N content (GNC) as grain yield increased. Breeding was shown to increase N translocation (NTE) by an annual genetic gain of 1.33% and 0.33%, respectively, under HN and LN. N accumulation at the maturity stage was higher in the modern cultivars compared to the pre-modern cultivars, mainly as a result of increased N accumulation during the stem elongation phase. The N translocation capacity of the vegetative tissues increased, and the N translocation efficiency of the sheath and chaff were higher than that of the leaves. Important genetic improvement targets for high NUE include increasing pre-anthesis N assimilation ability and post-anthesis N translocation capacity. Furthermore improvements in wheat breeding should include increasing both N uptake and NHI to improve NUE and reverse the trend of declining GNC. • Higher genetic gain of grain yield and N use efficiency under better environment. • Modern cultivars had higher N accumulation, mainly raised during stem elongation phase. • N utilization efficiency increased at the expense of lower grain N content. • Enhanced N translocation and uptake was important for N use efficiency improvement.

Comparative transcriptome analysis of different nitrogen responses in low-nitrogen sensitive and tolerant maize genotypes

Although previous researches have greatly increased our general knowledge on plant responses to nitrogen (N) stress, a comprehensive understanding of the different responses in crop genotypes is still needed. This study evaluated 304 maize accessions for low-N tolerance under field conditions, and selected the low-N sensitive Ye478 and low-N tolerant Qi319 for further investigations. After a 5-day low-N treatment, the typical N-deficient phenotype with yellowing older leaves was observed in Ye478 but not in Qi319. After the 5-day low-N stress, 16 RNA libraries from leaf and root of Ye478 and Qi319 were generated. The differentially expressed genes (DEGs) in the root of Qi319 up-regulated by special N deficiency were mainly enriched in energy-related metabolic pathways, including tricarboxylic acid metabolic process and nicotinamide metabolic process. Consistent with yellowing older leaves only observed in Ye478, the special N deficiency-responsive DEGs related to thylakoid, chloroplast, photosynthetic membrane, and chloroplast stroma pathways were repressed by low-N stress in Ye478. A total of 216 transcription factors (TFs), including ZmNLP5, were identified as special N deficiency-responsive TFs between Qi319 and Ye478, indicating the importance of transcriptional regulation of N stress-responsive pathway in different tolerance to low-N stress between crop genotypes. In addition, 15 miRNAs were identified as DEGs between Qi319 and Ye478. Taken together, this study contributes to the understanding of the genetic variations and molecular basis of low-N tolerance in maize.

Brassinosteroids modulate nitrogen physiological response and promote nitrogen uptake in maize (Zea mays L.)

Brassinosteroids (BRs) are steroid hormones that function in plant growth and development and response to environmental stresses and nutrient supplies. However, few studies have investigated the effect of BRs in modulating the physiological response to nitrogen (N) supply in maize. In the present study, BR signaling-deficient mutant zmbri1-RNAi lines and exogenous application of 2,4-epibrassinolide (eBL) were used to study the role of BRs in the regulation of physiological response in maize seedlings supplied with N. Exogenous application of eBL increased primary root length and plant biomass, but zmbri1 plants showed shorter primary roots and less plant biomass than wild-type plants under low N (LN) and normal N (NN) conditions. LN induced the expression of the BR signaling-associated genes ZmDWF4, ZmCPD, ZmDET2, and ZmBZR1 and the production of longer primary roots than NN. Knockdown of ZmBRI1 weakened the biological effects of LN-induced primary root elongation. eBL treatment increased N accumulation in shoots and roots of maize seedlings exposed to LN or NN treatment. Correspondingly, zmbri1 plants showed lower N accumulation in shoots and roots than wild-type plants. Along with reduced N accumulation, zmbri1 plants showed lower NO3− fluxes and 15NO3− uptake. The expression of nitrate transporter (NRT) genes (ZmNPF6.4, ZmNPF6.6, ZmNRT2.1, ZmNRT2.2) was lower in zmbri1 than in wild-type roots, but eBL treatments up-regulated the transcript expression of NRT genes. Thus, BRs modulated N physiological response and regulated the transcript expression of NRT genes to promote N uptake in maize.

Nitrogen addition stimulate random migration of plant community in a semiarid steppe

Increasing atmospheric nitrogen (N) deposition causes profound changes in the plant community, significantly threatening the terrestrial ecosystem function and stability worldwide. Random migration is a primary determinant of plant community assembly in the neutral model. However, whether its role is affected by N deposition is obscure. Therefore, the effects of eight N application rates (0, 1, 2, 3, 5, 10, 15, and 20 g N m−2 yr−1) on the estimated migration rate of plant community were examined in a long-term field study in a semiarid steppe. Our results indicated that N addition significantly impacted the estimated migration rate (F = 4.89, P < 0.001) and positively correlated with the N application rate (r2 = 0.32, P < 0.001). By constructing a structural equation model, we observed that the effect of N addition was mainly mediated through soil pH, moisture, and fungi: bacteria ratio. Mantel test revealed that the estimated migration rate was correlated with the plant community composition in moderate-N (10, 15, and 20 g N m−2 yr−1) treatment, but not in control (0 g N m−2 yr−1) and low-N treatment (1, 2, 3 and 5 g N m−2 yr−1) groups. Overall, our findings highlight the key role of N addition on plant community migration.

Genome-Wide Association Study and Identification of Candidate Genes for Nitrogen Use Efficiency in Barley (Hordeum vulgare L.).

Nitrogen (N) fertilizer is largely responsible for barley grain yield potential and quality, yet excessive application leads to environmental pollution and high production costs. Therefore, efficient use of N is fundamental for sustainable agriculture. In the present study, we investigated the performance of 282 barley accessions through hydroponic screening using optimal and low NH4NO3 treatments. Low-N treatment led to an average shoot dry weight reduction of 50%, but there were significant genotypic differences among the accessions. Approximately 20% of the genotypes showed high (>75%) relative shoot dry weight under low-N treatment and were classified as low-N tolerant, whereas 20% were low-N sensitive (≤55%). Low-N tolerant accessions exhibited well-developed root systems with an average increase of 60% in relative root dry weight to facilitate more N absorption. A genome-wide association study (GWAS) identified 66 significant marker trait associations (MTAs) conferring high nitrogen use efficiency, four of which were stable across experiments. These four MTAs were located on chromosomes 1H(1), 3H(1), and 7H(2) and were associated with relative shoot length, relative shoot and root dry weight. Genes corresponding to the significant MTAs were retrieved as candidate genes, including members of the asparagine synthetase gene family, several transcription factor families, protein kinases, and nitrate transporters. Most importantly, the high-affinity nitrate transporter 2.7 (HvNRT2.7) was identified as a promising candidate on 7H for root and shoot dry weight. The identified candidate genes provide new insights into our understanding of the molecular mechanisms driving nitrogen use efficiency in barley and represent potential targets for genetic improvement.

Natural variation and genomic prediction of growth, physiological traits, and nitrogen-use efficiency in perennial ryegrass under low-nitrogen stress.

Genomic prediction of nitrogen-use efficiency (NUE) has not previously been studied in perennial grass species exposed to low-N stress. Here, we conducted a genomic prediction of physiological traits and NUE in 184 global accessions of perennial ryegrass (Lolium perenne) in response to a normal (7.5 mM) and low (0.75 mM) supply of N. After 21 d of treatment under greenhouse conditions, significant variations in plant height increment (ΔHT), leaf fresh weight (LFW), leaf dry weight (LDW), chlorophyll index (Chl), chlorophyll fluorescence, leaf N and carbon (C) contents, C/N ratio, and NUE were observed in accessions , but to a greater extent under low-N stress. Six genomic prediction models were applied to the data, namely the Bayesian method Bayes C, Bayesian LASSO, Bayesian Ridge Regression, Ridge Regression-Best Linear Unbiased Prediction, Reproducing Kernel Hilbert Spaces, and randomForest. These models produced similar prediction accuracy of traits within the normal or low-N treatments, but the accuracy differed between the two treatments. ΔHT, LFW, LDW, and C were predicted slightly better under normal N with a mean Pearson r-value of 0.26, compared with r=0.22 under low N, while the prediction accuracies for Chl, N, C/N, and NUE were significantly improved under low-N stress with a mean r=0.45, compared with r=0.26 under normal N. The population panel contained three population structures, which generally had no effect on prediction accuracy. The moderate prediction accuracies obtained for N, C, and NUE under low-N stress are promising, and suggest a feasible means by which germplasm might be initially assessed for further detailed studies in breeding programs.

Characterization on TaMPK14, an MAPK family gene of wheat, in modulating N-starvation response through regulating N uptake and ROS homeostasis.

Wheat MAPK gene TaMPK14 is N starvation response and is crucial in modulating plant low-N stress tolerance. Improving plant N use efficiency (NUE) contributes largely to the sustainable crop production worldwide. In this study, TaMPK14, a mitogen-activated protein kinase (MAPK) family gene in T. aestivum, was characterized for the role in mediating N starvation response. TaMPK14 harbors conserved domain/motifs specified by the plant MAPK proteins. In vitro assay for kinase activity of TaMPK14 validated its phosphorylation nature. TaMPK14 transcripts were upregulated in both roots and leaves under low-N treatment; moreover, the expression levels induced by N starvation were gradually restored following the N recovery progression. These results suggested transcriptional response of TaMPK14 upon the low-N stress. Compared with wild type (WT), the TaMPK14 overexpressing lines in N. tabacum displayed improved growth and N accumulation traits under deficient-N treatment, which indicated the crucial roles of the MAPK gene in mediating N starvation response. Additionally, the lines treated by N starvation were shown to be improved on cellular ROS homeostasis, displaying higher antioxidant enzymes (AE) activities and less ROS accumulative amount than WT. The transcripts of nitrate transporter gene NtNRT2.1 and those of AE genes NtSOD1, NtCAT1;2, and NtPOD4 were significantly upregulated in N-deprived TaMPK14 lines; overexpression of them conferred plants enhanced N uptake capacity and AE activities, respectively. Moreover, RNA-seq datasets generated from N-deprived transgenic lines contained numerous differential genes involving modulating various biological process, cellular component, and molecular function. Together, our investigation suggested that TaMPK14 improves plant N starvation response through transcriptional regulation of distinct NRT and AE genes as well as modulation of associated biological processes.

Elevated concentrations of CO2 and nitrogen alter DOC release and soil phenolic content in wetland microcosms

ABSTRACTPhysiological responses of plants to elevated carbon dioxide (CO2) and nitrogen (N) availability are ecologically important because of increased atmospheric CO2 concentrations and N enrichment in many ecosystems. Here, the effects of N availability on the responses of six wetland plant species to elevated CO2 levels are examined in terms of growth and root exudation. Six species of emergent plant species typically found in marshes were incubated under two levels of CO2 (370 and 740 ppm) and two levels of N (0 and 8.8 mg N L−1). Elevated CO2 did not affect shoot biomass, root biomass, and height significantly, regardless of N levels. The C/N ratio of plant species increased in response to elevated CO2 levels, but this effect varied by species. All species released higher amounts of dissolved organic carbon under elevated CO2 compared with ambient air conditions. This response was limited under low soil N concentrations. By contrast, phenolic content increased significantly with elevated CO2 under low-N treatment. The findings suggest that elevated CO2 is not responsible for biomass accumulation of emergent wetland plant species, but does elicit changes in the quantity and quality of root exudates, which are, in turn, dependent on N availability to plant species.

Variation in Root and Shoot Growth in Response to Reduced Nitrogen.

Recently, root traits have been suggested to play an important role in developing greater nitrogen uptake and grain yield. However, relatively few breeding programs utilize these root traits. Over a series of experiments at different growth stages with destructive plant biomass measurements, we analyzed above-ground and below-ground traits in seven geographically diverse lines of wheat. Root and shoot biomass allocation in 14-day-old seedlings were analyzed using paper roll-supported hydroponic culture in two Hoagland solutions containing 0.5 (low) and 4 (high) mM of nitrogen (N). For biomass analysis of plants at maturity, plants were grown in 7.5 L pots filled with soil mix under two nitrogen treatments. Traits were measured as plants reached maturity. High correlations were observed among duration of vegetative growth, tiller number, shoot dry matter, and root dry matter. Functionality of large roots in nitrogen uptake was dependent on the availability of N. Under high N, lines with larger roots had a greater yield response to the increase in N input. Under low N, yields were independent of root size and dry matter, meaning that there was not a negative tradeoff to the allocation of more resources to roots, though small rooted lines were more competitive with regards to grain yield and grain N concentration in the low-N treatment. In the high-N treatment, the large-rooted lines were correlated to an increase in grain N concentration (r = 0.54) and grain yield (r = 0.43). In low N, the correlation between root dry matter to yield (r = 0.20) and grain N concentration (r = −0.38) decreased. A 15-fold change was observed between lines for root dry matter; however, only a ~5-fold change was observed in shoot dry matter. Additionally, root dry matter measured at the seedling stage did not correlate to the corresponding trait at maturity. As such, in a third assay, below-ground and above-ground traits were measured at key growth stages including the four-leaf stage, stem elongation, heading, post-anthesis, and maturity. We found that root growth appears to be stagnant from stem elongation to maturity.

Variability of maize inbred lines in nitrogen use effciency

Nitrogen (N) is an important element for many physiological processes in crops, and grain yield realisation. Nitrogen loss could be significant through leaching and evaporation, and from this reason lower quantities for fertilization are required. A genotype could be an important source for improved N management in crops. Breeding for high yield and nutrient-efficient genotypes is the most important strategy to enable food security, resolve resource scarcity and environmental pollution. Variability of 36 maize lines grown in optimal and low-N (without fertilization) conditions was assessed through grain yield, 1000 kernel weight, N utilization efficiency (NUtE) and N apparent recovery fraction (nitrogen use efficiency - NUE), during seasons 2017 and 2018. The genotype and year are important sources for variation of grain yield, 1000 kernel weight and NUtE, as a factor which defines N utilization efficiency. The lines, such as L1, L6, L13, L16, L26, L27, L32 and L34 are able to achieve higher grain yield when grown on low-N. Furthermore, L16, L22, L24 and L26 have high NUtE values in both experimental years (even in 2017, season with low and unequal precipitation level), especially in low-N treatment. From that point of view, they could be characterized as efficient N users, even in low-N conditions, as well as tolerant to stressful conditions. Nevertheless, L1, L6 and L27 are the lines with negative NUE, what gives them attribute as the best N users in low-N conditions. Based on the similarity of NUtE values, the genotypes such as L2, L3, L4, L8, L11, L12, L14, L15, L16, L18, L19, L24, L26, L32, L33, L34could be considered as the primary focus for further breeding programs, due to the fact that they don?t have only improved NUE, but also high grain yield (even in unfavourable years), which indicates improved tolerance to various abiotic stressful factors.

Physiological characteristics and metabolomics reveal the tolerance mechanism to low nitrogen in Glycine soja leaves.

To explore the regulatory mechanisms involved in the adaption to nitrogen (N) deficiency of wild soybean, the ion balance, photosynthetic characteristics, metabolic and transcriptional changes in leaves of common and low N (LN)-tolerant wild soybean seedlings under LN stress were determined. The LN-tolerant wild soybean seedlings showed a stronger ability to maintain photosynthesis and nutrient balance than common wild soybean. A total of 52 differentially accumulated metabolites, mainly related to carbon and N metabolism, were identified between the control and the LN treatment group. In general, tricarboxylic acid (TCA) cycle, shikimic acid pathway, synthetase/glutamate synthase (GS/GOGAT) cycle and accumulation of most organic acids were enhanced in LN-tolerant wild soybean, while reduced in common wild soybean under LN stress compared with their respective control group. Moreover, glycolysis, sugar and polyol and fatty acid metabolism increased in both wild soybean genotypes, and increased more in LN-tolerant wild soybean. A total of 3381 differentially expressed genes (DEGs) were identified in leaves of both wild soybean genotypes and the expressed level of DEGs associated with sugars, polyols, fatty acids and energy metabolism was significantly higher in LN-tolerant wild soybean than in common wild soybean, consistent with changes in metabolite level. Our results suggest new ideas for the study of LN tolerance of wild soybean and provide a theoretical basis for development and utilization of wild soybean resources.