Excessive nitrogen application under moderate soil water deficit decreases photosynthesis, respiration, carbon gain and water use efficiency of maize

Nitrogen deposition mitigates ozone-induced stress in Quercus aliena: Transcriptomic and metabolomic perspectives

Ozone (O3) pollution poses an increasingly serious threat to forest ecosystems. To investigate the effects of O3 exposure on Quercus aliena and elucidate its defense mechanisms, we exposed Q. aliena to O3 and monitored its responses using physiological, transcriptomic, and metabolomic analyses. The results revealed that after 84 days of O3 exposure, the malondialdehyde (MDA) and proline contents in Q. aliena leaves significantly increased, while catalase (CAT) activity and soluble sugar content significantly decreased. Notably, N addition markedly alleviated O3-induced oxidative stress. Integrated transcriptomic and metabolomic analyses revealed that N addition under O3 stress modulated metabolic pathways associated with flavonoid biosynthesis and amino acid metabolism. Specifically, O3 and N treatment increased the levels of rhoifolin, afzelechin, apigenin, luteoloside, kaempferol, and trifolin, while reducing the levels of phloretin, butin, cyanidin, taxifolin, myricetin, 2'-hydroxydaidzein, laricitrin, quercetin, prunin, luteolin, eriodictyol, quercitrin, and dihydromyricetin. Additionally, the co-treatment elevated the concentrations of L-glutamine, arginine, and ornithine, along with the levels of enzymes closely related to their synthesis, such as glnA (Uni0006561, Uni0006562, Uni0077758, Uni0101990), GSH (Uni0086646, Uni0101788), GSS (Uni0037737), and GCLC (Uni0034253). This study elucidates the metabolic alterations in Q. aliena under combined O3 and N treatments, highlighting changes in flavonoid biosynthesis and amino acid metabolism pathways. Using a multi-omics approach, we provide comprehensive insights into the responses of Q. aliena to O3 stress and N addition, offering significant implications for the management and conservation of forest ecosystems under environmental stress.

Integrative transcriptomic-physiological analysis deciphers nitrogen-mediated carbon reallocation balancing growth and flavonoid metabolism in Epimedium pubescens

Nitrogen availability critically shapes medicinal plant quality by coordinating the "growth-secondary metabolism" trade-off, yet its regulatory mechanisms remain elusive in the non-model species Epimedium pubescens. Through physiological-transcriptomic integration under five nitrogen levels (0, 3.5, 7.5,15, 22.5 mM NO3 -), we demonstrated that moderate nitrogen (MN: 7.5 mM NO3 -) optimally balanced biomass accumulation (22%-53% higher than low nitrogen [LN: 0 mM NO3 -] and high nitrogen [HN: 22.5 mM NO3 -]) with maximal Icariin-type flavonoid production (19%-34% higher than LN/HN). Extreme nitrogen stresses (LN/HN) impaired photosynthetic efficiency (18%-20% reduction), disrupted carbon-nitrogen homeostasis, and restricted flavonoid biosynthesis by hindering carbon reallocation (soluble sugars reduced by 26%-27%, starch by 30%-43%). Time-series transcriptomics revealed distinct response dynamics: LN triggered active transcriptional reprogramming at mid-stage (36 days after treatment, DAT), whereas HN responses were delayed to late-stage (48 DAT). Weighted gene co-expression network analysis (WGCNA) identified the grey60 module as a hub coordinating carbon-nitrogen metabolism and mRNA processing. A tripartite regulatory network linking nitrogen-responsive genes (e.g., EpF3H, UGT), Icariin-type flavonoid/carbon metabolism (e.g., icariin, soluble sugars), and growth phenotypes (e.g., biomass, photosynthesis) elucidated how nitrogen optimizes the trade-off between medicinal quality and yield in E. pubescens. This study provides molecular targets for precision nitrogen management to enhance both medicinal quality and yield, while establishing an integrative framework combining physiological and transcriptomic analyses to investigate metabolic trade-offs in non-model plants.

Response of Photosynthetic Capacity to Nitrogen Addition in Larix gmelinii Trees in Different Crown Classes

We explored the response of photosynthetic capacity to nitrogen (N) deposition among Larix gmelinii trees in different crown classes (e.g., suppressed, intermediate, and dominant trees) in a 12-year field experiment in a forest in the Greater Khingan Mountains in Northeast China. Four N-addition treatments were established: control (CK), low N (LN), medium N (MN), and high N (HN) (0, 25, 50, and 75 kg N·ha-1·year-1, respectively). Photosynthesis and its influencing factors were measured in 2023. Nitrogen addition significantly increased the maximum net photosynthetic rate (Pmax), maximum carboxylation rate (Vcmax), and maximum electron transport rate (Jmax) of suppressed and intermediate trees. The suppressed trees showed maximum Pmax and Vcmax in MN and HN, and maximum Jmax in HN. The intermediate trees showed maximum Pmax, Vcmax, and Jmax in MN. For dominant trees, Pmax was increased in LN and MN and decreased in HN, and Vcmax was increased by N addition and peaked in MN. Nitrogen addition significantly increased the leaf N content (Nmass), chlorophyll content (Chlm), the ratio of N to phosphorous (N:P), and photosynthetic enzyme activities in all crown classes. Nmass had significant nonlinear relationships with Pmax, Vcmax, and Jmax. Enzyme activity and Chlm positively affected the photosynthetic capacity of suppressed and intermediate trees, and N:P negatively affected the photosynthetic capacity of dominant trees. The promoting effect of N addition on photosynthetic capacity was stronger in suppressed and intermediate trees than in dominant trees. Therefore, the crown class should be considered when studying the effect of N deposition on the boreal forests.

Amino acid metabolism pathways as key regulators of nitrogen distribution in tobacco: insights from transcriptome and WGCNA analyses

BACKGROUND AND AIM

Nitrogen (N) is crucial for plant growth and is distributed across various N morphologies within plant organs. However, the mechanisms controlling the distribution of these N morphologies are not fully understood. This study investigated key amino acid (AA) biosynthesis pathways regulating N distribution and their impact on plant physiology and growth.

METHODS

We examined N distribution in the leaves, stems, and roots of two tobacco cultivars (Hongda and K326) under different N treatments at 75, and 100 days after transplanting (DAT). Transcriptome analysis was performed at 75 and 100 DAT to explore N distribution and AA metabolism pathways. Weighted gene co-expression network analysis (WGCNA) identified pathways regulating N distribution, and the Mantel test assessed the impact of N treatments, growth stages, and cultivars on N distribution.

RESULTS

Statistically significant differences in N distribution were observed across environmental conditions, growth stages, cultivars, and plant organs (p < 0.05). WGCNA identified phenylalanine metabolism (ko00360), alanine, aspartate, and glutamate metabolism (ko00250), and glycine, serine, and threonine metabolism (ko00260) pathways regulating the distribution of Nin-SDS (sodium dodecyl sulfate insoluble N), NW (water soluble N), and NS (sodium dodecyl sulfate soluble N), respectively. Increased N application promoted Nin-SDS accumulation, while earlier growth stages and cultivar Hongda favored NW distribution. NS distribution was inhibited under high N conditions. Gene expression in these pathways correlated with N distribution, biomass, and N accumulation.

CONCLUSION

This study elucidates the mechanisms regulating N distribution in tobacco, emphasizing the role of AA metabolism pathways. These findings are essential for improving N utilization and optimizing N management practices, ultimately enhancing crop productivity and supporting sustainable agricultural practices.

Water distribution within soil-plant-atmosphere system enhances water use efficiency at various nitrogen levels in Chinese paddy fields

Various nitrogen (N) fertilizer applications aim to achieve higher yields, reduce carbon emissions, or improve N use efficiency. However, enhancing water use efficiency (WUE) remains a significant challenge in Chinese paddy fields, with current N practices largely overlooking this aspect. Thus, this study aimed to estimate WUE by examining water transpiration, evaporation, leaching, and runoff across N application levels of 0-400 kg N ha-1 in Chinese rice fields using a data-intensive approach and the denitrification-decomposition (DNDC) model to optimize water resource utilization for sustainable rice production. Results revealed distinct WUE patterns: N inputs of 50-100 kg N ha-1 (N50-100) exhibited the highest WUE (10.38 kg mm-1), while 150-200 kg N ha-1 inputs (N150-200) achieved a high WUE (8.31 kg mm-1). In contrast, 250-400 kg N ha-1 (N250-400) showed the lowest WUE (7.74 kg mm-1). N50-100 reduced water transpiration, leaching, and runoff by 13-21 %, and increased water evaporation by 3 % compared to other N levels. These synergistic effects improved WUE; however, N50-100 may disrupt water equilibrium and kinetic fractionation by affecting water transpiration and leaching to limit the water productivity potential. N150-200 minimized evaporation by 38 % while sustaining high transpiration, thereby maintaining both water productivity and WUE. Conversely, N250-400 elevated water losses through transpiration, evaporation, and leaching, leading to reduced WUE. In conclusion, optimizing deeper soil water dynamics by limiting leaching and improving transpiration, especially within the widely practiced N150-200 range, shows promise for enhancing WUE potential in Chinese paddy fields. This study offers valuable insights into optimizing water resource utilization through targeted N fertilizer practices to achieve sustainable, low-carbon, and high-efficiency rice production.

Nondestructively-measured leaf ammonia emission rates can partly reflect maize growth status

A deep understanding of ammonia (NH3) emissions from cropland can promote efficient crop production. To date, little is known about leaf NH3 emissions because of the lack of rapid detection methods. We developed a method for detecting leaf NH3 emissions based on portable NH3 sensors. The study aimed to (i) determine the performance of the method in detecting leaf NH3 emissions; (ii) analyze the variation of leaf NH3 emissions with foliar rank; and (iii) elucidate the relationships between leaf NH3 emissions and other leaf parameters. Maize (Zea mays L.) was used as the tested plant. The results showed that the NH3 sensors had good repeatability, accuracy, and selectivity in detecting NH3. The response time of the method ranged 7-22 s and the NH3 reading ranged 0.078-0.463 μmol mol-1. Leaf NH3 emissions were observed mainly in daytime (negligible at night). Daytime leaf NH3 emission rates ranged 0.347-1.725 μg N cm-2 d-1. The middle leaves (near the ear) were the major contributor to plant NH3-N loss. There were significant linear relationships between leaf NH3 emission rates and other nondestructively-measured leaf parameters [e.g., SPAD (soil and plant analyzer development, which reflects the relative concentration of leaf chlorophyll), stomatal conductance, transpiration rate, and net photosynthetic rate] (p < 0.01), as well as with leaf apoplastic ammonium (NH4+) concentration and leaf total N concentration (p < 0.01). Nitrogen application increased leaf apoplastic NH4+ concentration, leaf total N concentration, and leaf NH3 emission rate. Overall, nondestructively-measured leaf NH3 emission rates can partly reflect maize growth status and provide information for N management in maize production.

Effects of Drought Stress on Photosynthesis and Chlorophyll Fluorescence in Blue Honeysuckle

Blue honeysuckle (Lonicera caerulea L.) is a deciduous shrub with perennial rootstock found in China. The objectives of this study were to explore the drought tolerance of blue honeysuckle, determine the effect of drought stress on two photosystems, and examine the mechanism of acquired drought tolerance. In this study, blue honeysuckle under four levels of simulated field capacity (100%, 85%, 75%, and 65% RH) was grown in split-root pots for drought stress treatment, for measuring the changes in chlorophyll content, photosynthetic characteristics, and leaf chlorophyll fluorescence parameters. The chlorophyll content of each increased under mild stress and decreased under moderate and severe stress. The net photosynthetic rate, transpiration rate, intercellular carbon dioxide concentration, and stomatal conductance of blue honeysuckle decreased with the increase in water stress. However, the water utilization rate and stomatal limit system increased under mild and moderate stress and decreased under severe stress. The maximum fluorescence (Fm), maximum photochemical efficiency, and quantum efficiency of photosystem II decreased with the decrease in soil water content, and the initial fluorescence increased significantly (p < 0.01). With the decrease in soil water content, the energy allocation ratio parameters decreased under severe drought stress. The main activity of the unit reaction center parameters first increased and then decreased. ABS/CSm, TRo/CSm, ETo/CSm, and REo/CSm gradually declined. After a comprehensive analysis, the highest scores were obtained under adequate irrigation (CK). Overall, we concluded that the water irrigation system of blue honeysuckle should be considered adequate.

Arabidopsis calcium-dependent protein kinase CPK6 regulates drought tolerance under high nitrogen by the phosphorylation of NRT1.1

Nitrogen (N) is an essential macronutrient for plant growth and development, and its availability is regulated to some extent by drought stress. Calcium-dependent protein kinases (CPKs) are a unique family of Ca2+ sensors with diverse functions in N uptake and drought-tolerance signaling pathways; however, how CPKs are involved in the crosstalk between drought stress and N transportation remains largely unknown. Here, we identify the drought-tolerance function of Arabidopsis CPK6 under high N conditions. CPK6 expression was induced by ABA and drought treatments. The mutant cpk6 was insensitive to ABA treatment and low N, but was sensitive to drought only under high N conditions. CPK6 interacted with the NRT1.1 (CHL1) protein and phosphorylated the Thr447 residue, which then repressed the NO3- transporting activity of Arabidopsis under high N and drought stress. Taken together, our results show that CPK6 regulates Arabidopsis drought tolerance through changing the phosphorylation state of NRT1.1, and improve our knowledge of N uptake in plants during drought stress.

Nitrogen supply alleviates cold stress by increasing photosynthesis and nitrogen assimilation in maize seedlings

Cold stress inhibits the early growth of maize, leading to reduced productivity. Nitrogen (N) is an essential nutrient that stimulates maize growth and productivity, but the relationship between N availability and cold tolerance is poorly characterized. Therefore, we studied the acclimation of maize under combined cold stress and N treatments. Exposure to cold stress caused a decline in growth and N assimilation, but increased abscisic acid (ABA) and carbohydrate accumulation. The application of different N concentrations from the priming stage to the recovery period resulted in the following observations: (i) high N supply alleviated cold stress-dependent growth inhibition, as shown by increased biomass, chlorophyll and Rubisco content and PSII efficiency; (ii) cold stress-induced ABA accumulation was repressed under high N, presumably due to enhanced stomatal conductance; (iii) the mitigating effects of high N on cold stress could be due to the increased activities of N assimilation enzymes and improved redox homeostasis. After cold stress, the ability of maize seedlings to recover increased under high N treatment, indicating the potential role of high N in the cold stress tolerance of maize seedlings.

Increasing the yield of drip-irrigated rice by improving photosynthetic performance and enhancing nitrogen metabolism through optimizing water and nitrogen management

Drip irrigation under plastic film mulching is an important technique to achieve water-conserving and high-efficiency rice (Oryza sativa L.) production in arid areas, but the grain yield of drip-irrigated rice is much lower than the expected yield (10.9-12.05 t·hm^-2) in practical production applications. Therefore, we hope to further understand the photosynthetic physiological mechanism of drip-irrigated rice yield formation by optimizing water and nitrogen management during the growth period and provide a scientific reference for improving yield and nitrogen use efficiency (NUE) of drip-irrigated rice in arid areas. In 2020 and 2021, T-43 (a drought-resistant; V1) and Liangxiang-3 (a drought-sensitive cultivar; V2) were cultivated under two water treatments (W₁: limited drip irrigation, 10200 m³·hm^-2; W₂: deficit drip irrigation, 8670 m³·hm^-2) and three nitrogen fertilization modes with different ratios of seedling fertilizer:tillering fertilizer:panicle fertilizer:grain fertilizer (N₁, 30%:50%:13%:7%; N₂, 20%:40%:30%:10%; and N₃, 10%:30%:40%:20%). The photosynthetic characteristics, nitrogen metabolism, yield, and NUE were analysed. The results showed that compared with other treatments, the W₁N₂ resulted in 153.4-930.3% higher glutamate dehydrogenase (GDH) contents and 19.2-49.7% higher net photosynthetic rates (P _n) in the leaves of the two cultivars at 20 days after heading, as well as higher yields and NUE. The two cultivars showed no significant difference in the physiological changes at the panicle initiation stage, but the P _n, abscisic acid (ABA), indole acetic acid (IAA), gibberellic acid (GA₃), and zeatin riboside (ZR) levels of V1 were higher than those of V2 by 53.1, 25.1, 21.1, 46.3 and 36.8%, respectively, at 20 days after heading. Hence, V1 had a higher yield and NUE than V2. Principal component analysis revealed that P _n and GDH were the most important physiological factors affecting rice yield performance. In summary, the W₁N₂ treatment simultaneously improved the yield and NUE of the drought-resistant rice cultivar (T-43) by enhancing the photosynthetic characteristics and nitrogen transport capacity and coordinating the balance of endogenous hormones (ABA, IAA, GA₃, and ZR) in the leaves.

Leaf Photosynthetic and Functional Traits of Grassland Dominant Species in Response to Nutrient Addition on the Chinese Loess Plateau

Leaf photosynthetic and functional traits of dominant species are important for understanding grassland community dynamics under imbalanced nitrogen (N) and phosphorus (P) inputs. Here, the effects of N (N0, N50, and N100, corresponding to 0, 50, and 100 kg ha^-1 yr^-1, respectively) or/and P additions (P0, P40, and P80, corresponding to 0, 40, and 80 kg ha^-1 yr^-1) on photosynthetic characteristics and leaf economic traits of three dominant species (two grasses: Bothriochloa ischaemum and Stipa bungeana; a leguminous subshrub: Lespedeza davurica) were investigated in a semiarid grassland community on the Loess Plateau of China. Results showed that, after a three-year N addition, all three species had higher specific leaf area (SLA), leaf chlorophyll content (SPAD value), maximum net photosynthetic rate (P_Nmax), and leaf instantaneous water use efficiency (WUE), while also having a lower leaf dry matter content (LDMC). The two grasses, B. ischaemum and S. bungeana, showed greater increases in P_Nmax and SLA than the subshrub L. davurica. P addition alone had no noticeable effect on the P_Nmax of the two grasses while it significantly increased the P_Nmax of L. davurica. There was an evident synergetic effect of the addition of N and P combined on photosynthetic traits and most leaf economic traits in the three species. All species had relatively high P_Nmax and SLA under the addition of N50 combined with P40. Overall, this study suggests that N and P addition shifted leaf economic traits towards a greater light harvesting ability and, thus, elevated photosynthesis in the three dominant species of a semiarid grassland community, and this was achieved by species-specific responses in leaf functional traits. These results may provide insights into grassland restoration and the assessment of community development in the context of atmospheric N deposition and intensive agricultural fertilization.

Screening of differentially expressed microRNAs and target genes in two potato varieties under nitrogen stress

BACKGROUND

A reasonable supply of nitrogen (N) fertilizer is essential for obtaining high-quality, high-level, and stable potato yields, and an improvement in the N utilization efficiency can effectively reduce N fertilizer use. It is important to use accurate, straightforward, and efficient transgenic breeding techniques for the identification of genes that can improve nitrogen use efficiency, thus enabling us to achieve the ultimate goal of breeding N-efficient potato varieties. In recent years, some of the mechanisms of miRNAs have been elucidated via the analysis of the correlation between the expression levels of potato miRNA target genes and regulated genes under conditions of stress, but the role of miRNAs in the inhibition/expression of key genes regulating N metabolism under N stress is still unclear. Our study aimed to identify the role played by specific enzymes and miRNAs in the responses of plants to N stress.

RESULTS

The roots and leaves of the N-efficient potato variety, Yanshu4 ("Y"), and N-inefficient potato variety, Atlantic ("D"), were collected at the seedling and budding stages after they were exposed to different N fertilizer treatments. The miRNAs expressed differentially under the two types of N stress and their corresponding target genes were first predicted using miRNA and degradome analysis. Then, quantitative polymerase chain reaction (qRT-PCR) was performed to verify the expression of differential miRNAs that were closely related to N metabolism. Finally, the shearing relationship between stu-miR396-5p and its target gene StNiR was determined by analyzing luciferase activity levels. The results showed that NiR activity increased significantly with an increase in the applied N levels from the seedling stage to the budding stage, and NiR responded significantly to different N treatments. miRNA sequencing enabled us to predict 48 families with conserved miRNAs that were mainly involved in N metabolism, carbon metabolism, and amino acid biosynthesis. The differences in the expression of the following miRNAs were identified via screening (high expression levels and P < 0.05): stu-miR396-5p, stu-miR408b-3p_R-1, stu-miR3627-3p, stu-miR482a-3p, stu-miR8036-3p, stu-miR482a-5p, stu-miR827-5p, stu-miR156a_L-1, stu-miR827-3p, stu-miR172b-5p, stu-miR6022-p3_7, stu-miR398a-5p, and stu-miR166c-5p_L-3. Degradome analysis showed that most miRNAs had many-to-many relationships with target genes. The main target genes involved in N metabolism were NiR, NiR1, NRT2.5, and NRT2.7. qRT-PCR analysis showed that there were significant differences in the expression levels of stu-miR396-5p, stu-miR8036-3p, and stu-miR482a-3p in the leaves and roots of the Yanshu4 and Atlantic varieties at the seedling and budding stages under conditions that involved no N and excessive N application; the expression of these miRNAs was induced in response to N stress. The correlation between the differential expression of stu-miR396-5p and its corresponding target gene NiR was further verified by determining the luciferase activity level and was found to be strongly negative.

CONCLUSION

The activity of NiR was significantly positively correlated with N application from the seedling to the budding stage. Differential miRNAs and target genes showed a many-to-many relationship with each other. The expression of stu-miR396-5p, stu-miR482a-3p, and stu-miR8036-3p in the roots and leaves of the Yanshu4 and Atlantic varieties at the seedling and budding stages was notably different under two types of N stress. Under two types of N stress, stu-miR396-5p was down-regulated in Yanshu4 in the seedling-stage and shoot-stage roots, and up-regulated in seedling-stage roots and shoot-stage leaves; stu-miR482a-3p was up-regulated in the seedling and shoot stages. The expression of stu-miR8036-3p was up-regulated in the leaves and roots at the seedling and budding stages, and down-regulated in roots under both types of N stress. The gene expressing the key enzyme involved in N metabolism, StNiR, and the stu-miR396-5p luciferase assay reporter gene had a strong regulatory relationship with each other. This study provides candidate miRNAs related to nitrogen metabolism and highlights that differential miRNAs play a key role in nitrogen stress in potato, providing insights for future research on miRNAs and their target genes in nitrogen metabolic pathways and breeding nitrogen-efficient potatoes.