Nitrate Conditions Research Articles

Evolutionary dynamics of nitrate uptake, assimilation, and signalling in plants: adapting to a changing environment.

Nitrogen (N) is a crucial macronutrient for plant growth, with nitrate as a primary inorganic N source for most plants. Beyond its role as a nutrient, nitrate also functions as a signalling molecule, influencing plant morphogenetic development. While nitrate utilization and signalling mechanisms have been extensively studied in model plants, the origin, evolution, and diversification of core components in nitrate uptake, assimilation, and signalling remain largely unexplored. In our investigation, we discovered that deep sea algae living in low nitrate conditions developed a high-affinity transport system (HATS) for nitrate uptake and a pathway of nitrate primary assimilation (NR-NiR-GS-GOGAT). In contrast, low-affinity transport systems (LATS) and the plastid GS originated from the ancestors of land and seed plants, respectively. These adaptations facilitated amino acid acquisition as plants conquered terrestrial environments. Furthermore, the intricate nitrate signalling, relying on NRT1.1 and NLP7, evolved stepwise, potentially establishing systematic regulation in bryophytes for self-regulation under complex terrestrial nitrate environments. As plants underwent terrestrialization, they underwent adaptive changes to thrive in dynamic nitrate environments, continually enhancing their nitrate uptake, assimilation, and signal transduction abilities.

Phosphorylation of Arabidopsis NRT1.1 regulates plant stomatal aperture and drought resistance in low nitrate condition

BackgroundNITRATE TRANSPORTER 1.1 (NRT1.1) functions as a dual affinity nitrate transceptor regulated by phosphorylation at threonine residue 101 (T101). Previous studies have suggested that NRT1.1 is involved in stomatal opening and contributes to drought susceptibility. However, the precise mechanism of how the phosphorylation status of NRT1.1 affects stomatal movement and drought tolerance remains unclear.ResultsIn this study, we observed that seedlings expressing the phosphorylated form of NRT1.1 (NRT1.1T101D, T101D) exhibited increased drought tolerance compared to dephosphorylated NRT1.1 (NRT1.1T101A, T101A) mutants under low nitrate (LN) condition, characterized by decreased stomatal aperture and water loss. Moreover, we found that the drought-induced depolarization of membrane potential was diminished in T101D mutants in comparison to T101A seedlings. Furthermore, we revealed that the reduced stomatal opening in T101D seedlings was related with depressed nitrate and potassium influx, along with the down-regulation of NRT1.1, POTASSIUM CHANNEL IN ARABIDOPSIS THALIANA 1, and ARABIDOPSISH+ATPase 1 in comparison with that of T101A.ConclusionsOur study provides several lines of evidence to demonstrate that the phosphorylation of NRT1.1 at T101 contributes to the drought tolerance under LN condition by reducing the influx of nitrate and potassium into the cytoplasm, attenuating membrane depolarization and thereby inducing stomatal closure. This finding identified a novel drought resistance mechanism enabled by post-transcriptional regulation of plasma membrane transporter.

Identification and Characterization of Key Genes for Nitrogen Utilization from Saccharum spontaneum Sub-Genome in Modern Sugarcane Cultivar.

Sugarcane (Saccharum spp.) is globally considered an important crop for sugar and biofuel production. During sugarcane production, the heavy reliance on chemical nitrogen fertilizer has resulted in low nitrogen use efficiency (NUE) and high loss. Up until now, there has been extensive research on the transcriptomic dynamics during sugarcane response to low nitrogen (LN) stress. However, the specific contribution of S. spontaneum to the NUE of modern sugarcane remains unclear. In the present study, the comparative transcriptome analysis of two contrasting sugarcane cultivars in response to nitrogen deficiency was performed via the combination of genomes of S. spontaneum and S. officinarum. Sub-genome analysis indicated that S. spontaneum supports the high NUE of modern sugarcane by providing genes related to nitrogen and carbohydrate metabolism, photosynthesis, and amino acid metabolism. Additionally, the key genes involved in nitrogen metabolism from the S. spontaneum were successfully identified through weighted gene co-expression network analyses (WGCNA), and a high-affinity nitrate transporter named ScNRT2.3 was subsequently cloned. Heterogeneous expression of the ScNRT2.3, a cell membrane-localized protein, could enhance the growth of Arabidopsis under low nitrate conditions. Furthermore, a conserved protein module known as NAR2.1/NRT2.3 was shown to regulate the response to LN stress in sugarcane roots through molecular interaction. This work helps to clarify the contribution of S. spontaneum to the NUE in modern sugarcane, and the function of the ScNRT2.3 in sugarcane.

Synthesis and Biological Studies of Schiff Bases Derived from 4-methyl 7-Ethylcoumarin

New 7-ethyl-4-methyl coumarin derivatives bearing an azo methene group (C=N) were synthesized by a four-step process. The reaction between 7-ethylphenol and ethyl acetoacetate in the presence of sulfuric acid afforded 7-ethyl-4-methylcoumarin 1 in 90% yield. Nitration conditions (nitric acid and sulfuric acid) were then applied to product 1 to produce 6-nitro-7-ethyl-4-methycoumarin 2 and 8-nitro-4-methyl-7-ethylcoumarin 3. The temperature, the amount of starting materials, and the time of reaction were essential factors in obtaining a high yield of isomer 2 compared to the second isomer 3. The nitro groups at compounds 2 and 3 were then reduced with iron metal in an acidic medium to form the corresponding amino compounds 4 and 5, which were converted to Schiff base derivatives 6-17 via reaction with different substituted aromatic aldehydes. The synthesized compounds were characterized by FT-IR, 1H NMR, and 13C NMR spectroscopy. Evaluating the biological activities of the synthetic compounds was carried out against two bacteria: gram-positive bacteria (Staphylococcus aureus) and gram-negative bacteria (Escherichia coli) at 1×10-3 M; compound 15 showed a broad spectrum against these two types of bacteria compared to Vancomycin and Amikacin and against fungi compared to nystatin as a standard drug, but compound 7 showed stronger activities against fungi than the other synthesized compounds. In contrast, the rest of the compounds showed moderate activity against fungi compared with the same standard drag; in the antioxidant study, some new compounds showed powerful antioxidants compared with ascorbic acid as a stander reference by calculating the IC50. Compound 8 showed very good results as an antioxidant agent compared with the same standard.

Headspace-single drop microextraction based visual colorimetry for non-chromatographic speciation analysis of nitrite and nitrate in environmental water sample

In this work, a visual colorimetric method based on headspace-single drop microextraction (HS-SDME) was developed for the non-chromatographic speciation analysis of nitrite and nitrate. The method adequately exploited the individual chemical vapor conditions of nitrite and nitrate that were converted to NO by specific reductants. Gaseous NO underwent a diazotization reaction with chromogenic reagent through the HS-SDME process to change from colorless to purplish-red. Instead of using large, time-consuming and relatively complicated chromatographic equipment for separation, the species of nitrite and nitrate could be analyzed by simply changing the reagents. Meanwhile, the extraction method effectively mitigated the matrix interference of solution and improved the sensitivity of method, with intuitive discrimination of color by the naked eye. The limits of detection were 0.07 μg/mL for nitrite and 0.2 μg/mL for nitrate, respectively. This method has been applied to analysis of real environmental water samples, which also effectively extended the application scope of HS-SDME device.

Root endodermal suberization induced by nitrate stress regulate apoplastic pathway rather than nitrate uptake in tobacco (Nicotiana tabacum L.)

Nitrogen levels and distribution in the rhizosphere strongly regulate the root architecture. Nitrate is an essential nutrient and an important signaling molecule for plant growth and development. Hydroponic experiments were conducted to investigate the differences in endodermal suberization in tobacco (Nicotiana tabacum L.) roots at three nitrate levels. Nitrogen accumulation was detected in the roots, shoots, and xylem sap. Nitrate influx on the root surface was also measured using the non-invasive self-referencing microsensor technique (SRMT). RNA-Seq analysis was performed to identify the genes related to endodermal suberization, nitrate transport, and endogenous abscisic acid (ABA) biosynthesis. The results showed that root length, root-shoot ratio, nitrate influx on the root surface, and NiA and NRT2.4 genes were regulated to maintain the nitrogen nutrient supply in tobacco under low nitrate conditions. Low nitrate levels enhanced root endodermal suberization and hence reduced the apoplastic transport pathway, and genes from the KCS, FAR, PAS2, and CYP86 families were upregulated. The results of exogenous fluridone, an ABA biosynthesis inhibitor, indicated that suberization of the tobacco root endodermis had no relevance to radial nitrate transport and accumulation. However, ABA enhances suberization, relating to ABA biosynthesis genes in the CCD family and degradation gene ABA8ox1.

Extraction behaviors of minor actinides and rare earth elements with NTA amide extractants

ABSTRACT Nitrilotriacetamide (NTA amide) has been developed as an extractant for the mutual separation of minor actinides (MA; Am and Cm) and rare earth elements (REs) by solvent extraction. NTA amide is a tertiary amine in which the three carboxyl groups of nitrilotriacetic acid are amidated. NTA amides have six hydrophobic long-chain alkyl groups on the side chains, and they have enhanced solubility in organic solvents, thereby allowing for the use of nonpolar diluents, such as n-dodecane. This study examined the extraction behavior of MA and REs using four NTA amides with six side chains comprising n-octyl groups, 2-ethylhexyl groups, and a mixture of these groups. The results showed that the linear-type hexaoctyl NTA amide (HONTA) had the highest extraction ability for MA. Furthermore, the extraction behavior of MA and REs was different under low and high nitrate conditions, and that of scandium (Sc) was found to be considerably different depending on the side chains.

Transcriptomic responses to shifts in light and nitrogen in two congeneric diatom species.

Light and nitrogen availability are basic requirements for photosynthesis. Changing in light intensity and nitrogen concentration may require adaptive physiological and life process changes in phytoplankton cells. Our previous study demonstrated that two Thalassiosira species exhibited, respectively, distinctive physiological responses to light and nitrogen stresses. Transcriptomic analyses were employed to investigate the mechanisms behind the different physiological responses observed in two diatom species of the genus Thalassiosira. The results indicate that the congeneric species are different in their cellular responses to the same shifting light and nitrogen conditions. When conditions changed to high light with low nitrate (HLLN), the large-celled T. punctigera was photodamaged. Thus, the photosynthesis pathway and carbon fixation related genes were significantly down-regulated. In contrast, the small-celled T. pseudonana sacrificed cellular processes, especially amino acid metabolisms, to overcome the photodamage. When changing to high light with high nitrate (HLHN) conditions, the additional nitrogen appeared to compensate for the photodamage in the large-celled T. punctigera, with the tricarboxylic acid cycle (TCA cycle) and carbon fixation significantly boosted. Consequently, the growth rate of T. punctigera increased, which suggest that the larger-celled species is adapted for forming post-storm algal blooms. The impact of high light stress on the small-celled T. pseudonana was not mitigated by elevated nitrate levels, and photodamage persisted.

Combined salt and low nitrate stress conditions lead to morphophysiological changes and tissue-specific transcriptome reprogramming in tomato

Despite intense research towards the understanding of abiotic stress adaptation in tomato, the physiological adjustments and transcriptome modulation induced by combined salt and low nitrate (low N) conditions remain largely unknown. Here, three traditional tomato genotypes were grown under long-term single and combined stresses throughout a complete growth cycle. Physiological, molecular, and growth measurements showed extensive morphophysiological modifications under combined stress compared to the control, and single stress conditions, resulting in the highest penalty in yield and fruit size.The mRNA sequencing performed on both roots and leaves of genotype TRPO0040 indicated that the transcriptomic signature in leaves under combined stress conditions largely overlapped that of the low N treatment, whereas root transcriptomes were highly sensitive to salt stress. Differentially expressed genes were functionally interpreted using GO and KEGG enrichment analysis, which confirmed the stress and the tissue-specific changes. We also disclosed a set of genes underlying the specific response to combined conditions, including ribosome components and nitrate transporters, in leaves, and several genes involved in transport and response to stress in roots. Altogether, our results provide a comprehensive understanding of above- and below-ground physiological and molecular responses of tomato to salt stress and low N treatment, alone or in combination.

Exogenous GA3 Enhances Nitrogen Uptake and Metabolism under Low Nitrate Conditions in 'Duli' (Pyrus betulifolia Bunge) Seedlings.

'Duli' (Pyrus betulifolia Bunge) is one of the main rootstocks of pear trees in China. Gibberellin (GA) is a key plant hormone and the roles of GA in nitrate (NO3-) uptake and metabolism in plants remain unclear. In this study, we investigated the effects of exogenous GA3 on the N metabolism of 'Duli' seedlings under NO3- deficiency. The results showed that exogenous GA3 significantly improves 'Duli' growth under NO3- deficiency. On the one hand, GA3 altered the root architecture, increased the content of endogenous hormones (GA3, IAA, and ZR), and enhanced photosynthesis; on the other hand, it enhanced the activities of N-metabolizing enzymes and the accumulation of N, and increased the expression levels of N absorption (PbNRT2) and the metabolism genes (PbNR, PbGILE, PbGS, and PbGOGAT). However, GA3 did not delay the degradation of chlorophyll. Paclobutrazol had the opposite effect on growth. Overall, GA3 can increase NO3- uptake and metabolism and relieve the growth inhibition of 'Duli' seedlings under NO3- deficiency.

Effects of Limiting Nitrate Concentration on Morphological and Differential Expression of High- and Low-Affinity Nitrate Transporter Genes of Diverse Wheat Genotypes

Nitrate uptake in wheat is an essential and complex process that involves multiple proteins. Roots are the major plant organs that take nitrate molecules from the soil and transport them to the above-ground parts. They involve several high- and low-affinity nitrate transporters located in the plasma membrane of different root and shoot tissues. In the present study, we investigated the responses of different selected wheat genotypes, released in India for different agroclimatic regions in a different year, for their biomass, root traits, and expression of high- and low-affinity nitrate transporters genes under optimal and limiting nitrate conditions at the 14 days seedling stage. The maximum number of genotypes showed increased biomass and total root size (TRS) under nitrate starvation, which indicates that the variation of TRS traits in different genotypes responds differently to nitrate starvation. Gene expression of TaNRT2.1-4 showed up-regulated expression under low external N-concentration in all genotypes. Among the four TaNRT1.1 orthologs, TaNPF6.1 and TaNPF6.4 showed up-regulated expression, whereas TaNPF6.2 and TaNPF6.3 expressed down-regulated in root at higher nitrate concentrations. TaNRT1.1 (TaNPF7.1 and TaNPF7.2) showed up-regulated in root at optimum nitrate concentrations. TaNPF6.1, TaNPF6.4, TaNPF7.1, and TaNPF7.2 showed a typical expression of low-affinity nitrate transporter genes under optimum external N-concentrations. Our findings indicate that HD2967, NP890, and VL804 showed the highest expression of TaNRT2.1-4, TaNRT1.1, and TaNRT1.5, respectively, possibly involved in nitrate uptake and translocation (from root to shoot).

Feeding on stressed algae exerts important effects on life history traits of Daphnia magna in a multi-stressor environment

Freshwater ecosystems are increasingly exposed to anthropogenic eutrophication, including high nitrogen. In addition, climate change is leading to more intense and frequent heatwaves, which have enormous impacts on all trophic levels of the ecosystem. Any change in the lower trophic levels, e.g., the phytoplankton, also introduces stress to higher trophic levels e.g., the zooplankton crustacean Daphnia. Individual effects of heatwaves, high nitrate, and changing feed quality have been studied in daphnia, but less is known about their interactive effects. This study used a 3 × 3 × 2 factorial design in which daphnia were exposed to combinations of ecologically relevant nitrate concentrations (0, 50, or 200 mg/L) and different heatwave scenarios (no, short-moderate, or long-intense) in which individuals were either fed with microalgae (P. subcapitata and C. reinhardtii) grown at 20 °C and 50 mg/L nitrate (control feed) or the same conditions as daphnia was exposed to (experimental feed). Throughout the experiment, the interactive effects of high nitrate, heatwave, and feed on mortality, maturation, offspring, and body size were evaluated. In general, heatwaves shorten the lifespan of daphnia. Exposing daphnia to a long-intense heatwave combined with high nitrate resulted in poor performance. In the nitrate-limited condition, however, the restricted proliferation of microalgae reduced feed availability, which also had a major impact on daphnia's life history traits. Daphnia cultured in high nitrate and fed control feed performed better than when fed experimental feed, suggesting that in a high nitrate condition, the microalgae grown under the same experimental conditions was either unable to meet energy requirements or introduced extra stress for the daphnia. Most importantly, the effect of nitrate and heatwave as stressors on the availability and quality of the feed had a greater impact on daphnia than its direct impact. Interestingly, a transgenerational adaptation to nitrate was observed which may help to maintain ecological balance in the long run.

Toxin production and transcriptomic response to nitrate concentrations in the toxic dinoflagellate Alexandrium tamarense

The bloom-forming dinoflagellate Alexandrium tamarense is one of the most important producers of paralytic shellfish poisoning toxins. Annually recurrent blooms of this dinoflagellate species is associated with the incremental nitrogen influx, especially excessive nitrate input. However, limited studies have been conducted on the toxin production and underlying molecular regulation mechanisms of A. tamarense under various nitrate (N) conditions. Therefore, toxin production and transcriptomic responses of this species were investigated. The toxin profile of A. tamarense was consistently dominated by the C2-toxins, and the cellular toxicity increased with N concentrations peaking at 9.23 ± 0.03 fmol/cell in the 883 μM N-added group. Under lower N conditions, expressions of two STX-core genes, sxtA and sxtG, were significantly down-regulated, suggesting that N regulated sxt expression and triggered responses related to toxin biosynthesis. Results of this study provided valuable insights into the ecophysiology of A. tamarense, enhancing our understanding of the occurrence of toxification events in natural environments.

Cytokinin Biosynthesis Is Affected by Selenium and Nitrate Availabilities to Regulate Shoot and Root Growth in Rice Seedlings

Selenium (Se) and nitrate have the potential to modify rice root architecture, but it is unclear how Se is linked to changes in the rice seedlings nitrate status. Thus, rice seedlings were grown in nutrient solutions containing either 0- or 10-µM Se that were supplemented with 0.05 (low nitrate condition) or 5.0 mM nitrate (high nitrate condition). Se application to seedlings treated with low nitrate led to sugar accumulation in shoot and root and increased cytokinin concentrations in root, while decreasing cytokinin concentrations in shoot compared with seedlings in 0.05 mM nitrate alone. This, in turn, resulted in decreased shoot growth, while downregulation of OsXTH and OsEXP negatively affected root expansion. On the other hand, Se combined with 5.0 mM nitrate did not affect sugar concentration in tissues compared with seedlings in 5.0 mM nitrate. Moreover, Se negatively regulated the cytokinin biosynthesis in shoot and root of seedlings grown under 5.0 mM nitrate. The reduction in cytokinin concentrations by Se under high nitrate condition decreased shoot growth, but increased root growth through induction of OsXTH and OsEXP. Thus, many of the effects of Se in shoot and root growth are due to a shift in nitrate status of the seedlings.

Comparative transcriptome study highlights the versatility of nitrogen metabolism in Chlamydomonas

Nitrogen is an essential macronutrient and nitrate is one of the main forms of this macronutrient available for plants and microbes. Nitrate is not only the substrate for the nitrate assimilation pathway, but also a crucial signal for the regulation of numerous metabolic, developmental, and cellular differentiation processes. In the present study, two species of the Chlamydomonas genus, Chlamydomonas reinhardtii cc124 and Chlamydomonas sp. MACC-216 were used to investigate the versatility of nitrate metabolism in green microalgae. Quantification of nitrate removal efficiency showed that Chlamydomonas sp. MACC-216 strongly outperforms C. reinhardtii cc124. Transcriptional changes occurring under nitrate-replete and nitrate-deplete conditions were specifically investigated in the selected species of Chlamydomonas. Whole transcriptome analysis revealed that the genes playing a role in nitrate assimilation did not show differential expression in C. reinhardtii cc124 under changing nitrate conditions (only 45 genes exhibited differential regulation), while in Chlamydomonas sp. MACC-216 a large set of genes (3143) showed altered expression. Furthermore, genes responsible for urea metabolism, like DUR3A gene corresponding to urea transport, were found to be upregulated in Chlamydomonas sp. MACC-216 under nitrate-deplete condition, while the same gene showed elevated expression level in C. reinhardtii cc124 under nitrate-replete condition. The present study indicated the diverseness of nitrate metabolism among species within the Chlamydomonas genus.

The endemic kelp Lessonia corrugata is being pushed above its thermal limits in an ocean warming hotspot.

Kelps are in global decline due to climate change, which includes ocean warming. To identify vulnerable species, we need to identify their tolerances to increasing temperatures and determine whether tolerances are altered by co-occurring drivers such as inorganic nutrient levels. This is particularly important for those species with restricted distributions, which may already be experiencing thermal stress. To identify thermal tolerance of the range-restricted kelp Lessonia corrugata, we conducted a laboratory experiment on juvenile sporophytes to measure performance (growth, photosynthesis) across its thermal range (4-22°C). We determined the upper thermal limit for growth and photosynthesis to be ~22-23°C, with a thermal optimum of ~16°C. To determine if elevated inorganic nitrogen availability could enhance thermal tolerance, we compared the performance of juveniles under low (4.5 μmol · d-1) and high (90 μmol · d-1) nitrate conditions at and above the thermal optimum (16-23.5°C). Nitrate enrichment did not enhance thermal performance at temperatures above the optimum but did lead to elevated growth rates at the thermal optimum. Our results indicate L. corrugata is likely to be extremely susceptible to moderate ocean warming and marine heatwaves. Peak sea surface temperatures during summer in eastern and northeastern Tasmania can reach up to 20-21°C, and climate projections suggest that L. corrugata's thermal limit will be regularly exceeded by 2050 as southeastern Australia is a global ocean-warming hotspot. By identifying the upper thermal limit of L. corrugata, we have taken a critical step in predicting the future of the species in a warming climate.

Nitrogen Nutrition Modulates the Response to Alternaria brassicicola Infection via Metabolic Modifications in Arabidopsis Seedlings.

Little is known about the effect of nitrogen nutrition on seedling susceptibility to seed-borne pathogens. We have previously shown that seedlings grown under high nitrate (5 mM) conditions are less susceptible than those grown under low nitrate (0.1 mM) and ammonium (5 mM) in the Arabidopsis-Alternaria brassicicola pathosystem. However, it is not known how seedling metabolism is modulated by nitrogen nutrition, nor what is its response to pathogen infection. Here, we addressed this question using the same pathosystem and nutritive conditions, examining germination kinetics, seedling development, but also shoot ion contents, metabolome, and selected gene expression. Nitrogen nutrition clearly altered the seedling metabolome. A similar metabolomic profile was observed in inoculated seedlings grown at high nitrate levels and in not inoculated-seedlings. High nitrate levels also led to specific gene expression patterns (e.g., polyamine metabolism), while other genes responded to inoculation regardless of nitrogen supply conditions. Furthermore, the metabolites best correlated with high disease symptoms were coumarate, tyrosine, hemicellulose sugars, and polyamines, and those associated with low symptoms were organic acids (tricarboxylic acid pathway, glycerate, shikimate), sugars derivatives and β-alanine. Overall, our results suggest that the beneficial effect of high nitrate nutrition on seedling susceptibility is likely due to nutritive and signaling mechanisms affecting developmental plant processes detrimental to the pathogen. In particular, it may be due to a constitutively high tryptophan metabolism, as well as down regulation of oxidative stress caused by polyamine catabolism.

Synergistic effect of nitrate exposure and heatwaves on the growth, and metabolic activity of microalgae, Chlamydomonas reinhardtii, and Pseudokirchneriella subcapitata

Aquatic biota are threatened by climate warming as well as other anthropogenic stressors such as eutrophication by phosphates and nitrate. However, it remains unclear how nitrate exposure can alter the resilience of microalgae to climate warming, particularly heatwaves. To get a better understanding of these processes, we investigated the effect of elevated temperature and nitrate pollution on growth, metabolites (sugar and protein), oxidative damage (lipid peroxidation), and antioxidant accumulation (polyphenols, proline) in Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata. The experiment involved a 3 × 3 factorial design, where microalgae were exposed to one of three nitrate levels (5, 50, or 200 mg L−1 NO3−l) at 20 °C for 2 weeks. Subsequently, two heatwave scenarios were imposed: a short and moderate heatwave at 24 °C for 2 weeks, and a long and intense heatwave with an additional 2 weeks at 26 °C. A positive synergistic effect of heatwaves and nitrate on growth and metabolites was observed, but this also led to increased oxidative stress. In the short and moderate heatwave, oxidative damage was controlled by increased antioxidant levels. The high growth, metabolites, and antioxidants combined with low oxidative stress during the short and moderate heatwaves in moderate nitrate (50 mg L−1) led to a sustainable increased food availability to grazers. On the other hand, long and intense heatwaves in high nitrate conditions caused unsustainable growth due to increased oxidative stress and relatively low antioxidant (proline) levels, increasing the risk for massive algal die-offs.

Nitrate stimulates adventitious rooting by increasing auxin content and regulating auxin- and root development-related genes expression in apple

Adventitious root (AR) formation is critical for cutting survival and nutrient absorption re-establishment. This complex genetic trait involves the interplay of nitrogen, endogenous hormones, and several key genes. In this study, we treated GL-3 apple (Malus domestica) in vitro shoots with nitrate and ammonium to determine their impact on AR formation, hormonal content, and gene expression patterns. Nitrate treatment significantly promotes adventitious rooting by increasing cell division, differentiation, and AR primordia formation compared to ammonium treatment. Elevated indole-3-acetic acid (IAA), reduced abscisic acid, and zeatin riboside concentrations were consistently observed with nitrate, likely crucial for promoting ARs over ammonium. Furthermore, Malus domestica auxin resistance1 (MdAUX1) expression was induced, increasing IAA levels. MdIAA23 was upregulated. Further results indicate that the higher expression levels of Malusdomestica WUSCHEL-relatedHomeobox gene 11 (MdWOX11), Malus domestica lateral organ boundariesdomaingene 16 (MdLBD16), and MdLBD29, and increased cell cycle-related gene expressions, contribute to auxin-stimulated adventitious rooting under nitrate conditions. In conclusion, this study establishes that auxin content and associated genes related to root development and cell cycle contribute to superior ARs in response to nitrate.

Storm characteristics influence nitrogen removal in an urban estuarine environment

Abstract. Sustaining water quality is an important component of coastal resilience. Floodwaters deliver reactive nitrogen (including NOx) to sensitive aquatic systems and can diminish water quality. Coastal habitats in flooded areas can be effective at removing reactive nitrogen through denitrification (DNF). However, less is known about this biogeochemical process in urbanized environments. This study assessed the nitrogen removal capabilities of flooded habitats along an urban estuarine coastline in the upper Neuse River estuary, NC, USA, under two nitrate concentrations (16.8 and 52.3 µM NOx, respectively). We also determined how storm characteristics (e.g., precipitation and wind) affect water column NOx concentrations and consequently DNF by flooded habitats. Continuous flow sediment core incubation experiments quantified gas and nutrient fluxes across the sediment–water interface in marsh, swamp forest, undeveloped open space, stormwater pond, and shallow subtidal sediments. All habitats exhibited net DNF. Additionally, all habitats increased DNF rates under elevated nitrate conditions compared to low nitrate. Structured habitats with high-sediment organic matter had higher nitrogen removal capacity than unstructured, low-sediment organic matter habitats. High-precipitation–high-wind-storm events produced NOx concentrations significantly lower than other types of storms (e.g., low-precipitation–high-wind, high-wind–low-precipitation, low-wind–low-precipitation), which likely results in relatively low DNF rates by flooded habitats and low removal percentages of total dissolved nitrogen loads. These results demonstrate the importance of natural systems to water quality in urbanized coastal areas subject to flooding.