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Nitrogen (N) is the driving force for crop yields; however, excessive N application in agriculture not only increases production cost, but also causes severe environmental problems. Therefore, comprehensively understanding the molecular mechanisms of N use efficiency (NUE) and breeding crops with higher NUE is essential to tackle these problems. NUE of crops is determined by N uptake, transport, assimilation, and remobilization. In the process of N assimilation, nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamine-2-oxoglutarate aminotransferase (GOGAT, also known as glutamate synthase) are the major enzymes. NR and NiR mediate the initiation of inorganic N utilization, and GS/GOGAT cycle converts inorganic N to organic N, playing a vital role in N assimilation and the final NUE of crops. Besides, asparagine synthetase (ASN), glutamate dehydrogenase (GDH), and carbamoyl phosphate synthetase (CPSase) are also involved. In this review, we summarize the function and regulation of these enzymes reported in three major crops-rice, maize, and wheat, also in the model plant Arabidopsis, and we highlight their application in improving NUE of crops via manipulating N assimilation. Anticipated challenges and prospects toward fully understanding the function of N assimilation and further exploring the potential for NUE improvement are discussed., Competing Interests: Conflict of interest The authors declare no competing interests., (Copyright © 2021 Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, and Genetics Society of China. Published by Elsevier Ltd. All rights reserved.)

Zero-valent iron (Fe 0 ) has been widely used for the reduction of nitrate, but the end reduction product is mainly ammonium. Here, a novel strategy for selective reduction of nitrate (NO 3 ) to nitrogen gas (N - ) to nitrogen gas (N 2 ) with high efficiency and N 2 selectivity was investigated using Fe-based material (Fe 0 -Cu 0 -CuFe 2 O 4 ) combined with citric acid (CA) and ultraviolet (UV) irradiation. In this strategy, the nitrate was firstly reduced to nitrite (NO 2 - ) by Fe 0 -Cu 0 -CuFe 2 O 4 /UV process, and then the produced NO 2 - could be further reduced to N 2 by carbon dioxide anion radicals (CO 2 •- ) which was generated from CA that was added later. In this process, the selective reduction of NO 3 - to NO 2 - was a key step. For this purpose, we synthesized Fe 0 -Cu 0 -CuFe 2 O 4 composite by simple chemical replacement and in-situ growth process, which made it have a delicate structure with good contact between Cu and Fe and CuFe 2 O 4 . The selective reduction of NO 3 - to NO 2 - in Fe 0 -Cu 0 -CuFe 2 O 4 /UV process was due to that the Cu 0 was the electron enrichment center and the photo-generated hole could suppress the NO 3 - reduction to NH 4 + by Fe 2+ . In this proposed strategy, 100% NO 3 - removal efficiency and 96.3% N 2 selectivity were achieved when the initial NO 3 - concentration was 30 mg N/L and the reduction time was 60 min. The denitrification mechanism of the Fe 0 -Cu 0 -CuFe 2 O 4 /UV/CA system was proposed., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Particulate organic carbon (POC) significantly influences nitrogen processes in riparian zones. However, the role of different types of natural organic matter (e.g., plant leaves and mud deposits) in nitrate reduction during the hydraulically driven mixing between rivers and groundwater within bank storage (BS) is not well known. Here, we used laboratory columns filled with 30 cm of riparian soil and buried with POC of varying quantity and quality (leaf litter, mud deposit, a mixture of both and a sediment control) on the soil surface in the column to investigate the effects of POC addition on nitrate reduction in low-permeable media. Pore waters were collected and measured periodically to compare the physicochemical differences among these treatments over time during scenarios of downward and upward flow. The leaf litter treatment had a larger amount of POC and higher reactivity, driving pore water to be in suboxic conditions with lower Eh and pH values. Nitrate reduction occurred immediately with downward surface water, and NO 3 was removed in the POC buried layer. Due to the low POC content and low reactivity of the carbon source in the mud deposit, denitrification primarily occurred in the deeper sediment during the downwelling stage, as well as when groundwater returned to the POC buried layer with longer travel times. Both POC quantity and POC quality had strong effects on nitrate reduction. Our results suggested that the leaf litter treatment was preferential for nitrate reduction over the mud deposit treatment, with a higher NO - was removed in the POC buried layer. Due to the low POC content and low reactivity of the carbon source in the mud deposit, denitrification primarily occurred in the deeper sediment during the downwelling stage, as well as when groundwater returned to the POC buried layer with longer travel times. Both POC quantity and POC quality had strong effects on nitrate reduction. Our results suggested that the leaf litter treatment was preferential for nitrate reduction over the mud deposit treatment, with a higher NO 3 - reduction rate and less NH 4 + accumulation during the complete BS process., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In order to expand the application of CO 2 anion radical (CO 2 - ), as a novel green reductant in the control of environmental pollution, CO 2 radical were investigated based on the results of batch experiments and theoretical calculation using density functional theory (DFT) methods, respectively. It was found that: (1) the efficiency of nitrate reduction by CO - radical from the HCOOH/UV system was far lower than that of nitrite under the same reaction conditions, (2) the rate-control step of nitrate reduction by CO 2 radical was the transformation process of nitrate into nitrite with an activation energy of 23.9 kcal/mol, (3) the final products of nitrate reduction were mainly composed of nitrogen (N - radical were investigated based on the results of batch experiments and theoretical calculation using density functional theory (DFT) methods, respectively. It was found that: (1) the efficiency of nitrate reduction by CO 2 - radical from the HCOOH/UV system was far lower than that of nitrite under the same reaction conditions, (2) the rate-control step of nitrate reduction by CO 2 - radical was the transformation process of nitrate into nitrite with an activation energy of 23.9 kcal/mol, (3) the final products of nitrate reduction were mainly composed of nitrogen (N 2 selectivity could reach 97.5%. This work provided a promising approach for the reduction of nitrate into nitrogen with high efficiency and high N 2 using CO 2 - radical was proposed. Specifically, nitrate was firstly reduced into nitrite with the assistance of Zn/Ag bimetal, and then nitrite was further reduced into N 2 by CO 2 - radical. In this way, the removal efficiency of nitrate was all achieved nearly 100% in the initial nitrate concentration ranging from 25 to 100 mg (N)/L, while the highest N 2 selectivity could reach 97.5%. This work provided a promising approach for the reduction of nitrate into nitrogen with high efficiency and high N 2 selectivity by CO 2 - radical., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Low-grade weirs placed within agricultural drainage ditches in the Lower Mississippi Alluvial Valley can be used as a management practice to enhance nitrogen removal. The addition of organic carbon amendments within ditches that contain weirs could further increase nitrogen removal. Through repeated trials, changes in NO 3 - -N concentration between inflow and outflow were variable in the ditch without weirs, while only decreases in concentration were observed in ditches with weirs. Significant differences in NO 3 - -N concentrations were observed between treatments, with greater removal of NO 3 - -N observed in dissolved organic carbon treatments compared to control and particulate organic carbon treatments. At medium- and high-flow rates, respectively, dissolved organic carbon treatments resulted in greater NO 3 - -N concentration decreases of 31.6% and 27.1% compared to 19% and 11.6% in particulate organic carbon treatments and 18.6% and 17.2% in control treatments. Significant effects of weirs and sampling date on nirS, nirK, nosZ, and 16S rRNA gene abundances were observed. Observed increases in NO 3 - -N removal with organic carbon amendments, provides support for continued investigation on improving the efficacy of organic carbon amendments as a best management practice for NO 3 - -N removal in agricultural drainage ditches. PRACTITIONER POINTS: Dissolved organic carbon amendments increased nitrate-nitrogen removal. Only decreases in nitrate-nitrogen concentration were observed in ditches with weirs. Increasing flow rate did not affect nitrate-nitrogen removal. Abundance of denitrification-performing microbes likely did not affect N removal. Lack of anaerobic soil conditions and short residence time reduced nitrate-N removal., (© 2019 Water Environment Federation.)

Sediment microbes have a great potential to transform reactive N to harmless N 2 , thus decreasing wastewater nitrogen load into aquatic ecosystems. Here, we examined if spatial allocation of the wastewater discharge by a specially constructed sediment diffuser pipe system enhanced the microbial nitrate reduction processes. Full-scale experiments were set on two Finnish lake sites, Keuruu and Petäjävesi, and effects on the nitrate removal processes were studied using the stable isotope pairing technique. All nitrate reduction rates followed nitrate concentrations, being highest at the wastewater-influenced sampling points. Complete denitrification with N 2 as an end-product was the main nitrate reduction process, indicating that the high nitrate and organic matter concentrations of wastewater did not promote nitrous oxide (N 2 O) production (truncated denitrification) or ammonification (dissimilatory nitrate reduction to ammonium; DNRA). Using 3D simulation, we demonstrated that the sediment diffusion method enhanced the contact time and amount of wastewater near the sediment surface especially in spring and in autumn, altering organic matter concentration and oxygen levels, and increasing the denitrification capacity of the sediment. We estimated that natural denitrification potentially removed 3-10% of discharged wastewater nitrate in the 33 ha study area of Keuruu, and the sediment diffusion method increased this areal denitrification capacity on average 45%. Overall, our results indicate that sediment diffusion method can supplement wastewater treatment plant (WWTP) nitrate removal without enhancing alternative harmful processes., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Elevated [CO2] and salinity in the soils are considered part of the effects of future environmental conditions in arid and semi-arid areas. While it is known that soil salinization decreases plant growth, an increased atmospheric [CO2] may ameliorate the negative effects of salt stress. However, there is a lack of information about the form in which inorganic nitrogen source may influence plant performance under both conditions. Single factor responses and the interactive effects of two [CO2] (380 and 800ppm), three different NO3(-)/NH4(+) ratios in the nutrient solution (100/0, 50/50 and 0/100, with a total N concentration of 3.5mM) and two NaCl concentrations (0 and 80mM) on growth, leaf gas exchange parameters in relation to root hydraulic conductance and N-assimilating enzymes of broccoli (Brassica oleracea L. var. Italica) plants were determined. The results showed that a reduced NO3(-) or co-provision of NO3(-) and NH4(+) could be an optimal source of inorganic N for broccoli plants. In addition, elevated [CO2] ameliorated the effect of salt exposure on the plant growth through an enhanced rate of photosynthesis, even at low N-concentration. However, NO3(-) or NO3(-)/NH4(+) co-provision display differential plant response to salt stress regarding water balance, which was associated to N metabolism. The results may contribute to our understanding of N-fertilization modes under increasing atmospheric [CO2] to cope with salt stress, where variations in N nutrition significantly influenced plant response., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A novel type of nitrate removal process was investigated in this study, which coupled nitrate reduction by zero-valent iron(ZVI) with anaerobic ammonia oxidation(AMAMMOX). The zero-valent iron dosage was 71 g·L -1 . The inoculation volume of ANAMMOX granular sludge was 200 mg·L -1 . The agitation rate and environment reaction temperature of the CSTR was set up to 150 r·min -1 and 33℃±0.5℃, respectively. The pH of influent was maintained at 7.0-8.0.The result indicated that ANAMMOX bacteria could survive in nitrate and ZVI supplied system under neutral condition. The reactor was set up quickly with the nitrogen removal rate of 0.12 kg·(m 3 ·d) -1 on the first 5 days, and maintained over 0.1 kg·(m 3 ·d) -1 nitrogen removal ability with the effluent nitrite and ammonia concentrations below 2.0 mg·L -1 and pH value higher than 8.0. The nitrogen loss was up to 89% under the condition of 30-40℃, pH 4-6.Too extreme pH and temperature conditions were not favorable for the coupling reactions.

Groundwater under industrial sites is characterised by heterogeneous chemical mixtures, making it difficult to assess the fate and transport of individual contaminants. Quantifying the in-situ biological removal (attenuation) of nitrogen (N) is particularly difficult due to its reactivity and ubiquity. Here a multi-isotope approach is developed to distinguish N sources and sinks within groundwater affected by complex industrial pollution. Samples were collected from 70 wells across the two aquifers underlying a historic industrial area in Belgium. Below the industrial site the groundwater contained up to 1000 mg N l(-1) ammonium (NH4(+)) and 300 mg N l(-1) nitrate (NO3(-)), while downgradient concentrations decreased to ∼1 mg l(-1) DIN ([DIN] = [NH4(+)N] + [NO3(-)N] + [NO2(-)N]). Mean δ(15)N-DIN increased from ∼2‰ to +20‰ over this flow path, broadly confirming that biological N attenuation drove the measured concentration decrease. Multi-variate analysis of water chemistry identified two distinct NH4(+) sources (δ(15)NNH4(+) from -14‰ and +5‰) within the contaminated zone of both aquifers. Nitrate dual isotopes co-varied (δ(15)N: -3‰ - +60‰; δ(18)O: 0‰ - +50‰) within the range expected for coupled nitrification and denitrification of the identified sources. The fact that δ(15)NNO2(-) values were 50‰-20‰ less than δ(15)NNH4(+) values in the majority of wells confirmed that nitrification controlled N turnover across the site. However, the fact that δ(15)NNO2(-) was greater than δ(15)NNH4(+) in wells with the highest [NH4(+)] shows that an autotrophic NO2(-) reduction pathway (anaerobic NH4(+) oxidation or nitrifier-denitrification) drove N attenuation closest to the contaminant plume. This direct empirical evidence that both autotrophic and heterotrophic biogeochemical processes drive N attenuation in contaminated aquifers demonstrates the power of multiple N isotopes to untangle N cycling in highly complex systems., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Dwarf bamboo (Fargesia rufa Yi), one of the staple foods for the endangered giant pandas, is highly susceptible to water deficit due to its shallow roots. In the face of climate change, maintenance and improvement in its productivity is very necessary for the management of the giant pandas' habitats. However, the regulatory mechanisms underlying plant responses to water deficit are poorly known. To investigate the effects of P application on photosynthetic C and N metabolism, water use efficiency (WUE) and growth of dwarf bamboo under water deficit, a completely randomized design with two factors of two watering (well-watered and water-stressed) and two P regimes (with and without P fertilization) was arranged. P application hardly changed growth, net CO2 assimilation rate (P(n)) and WUE in well-watered plants but significantly increased relative growth rate (RGR) and P(n) in water-stressed plants. The effect of P application on RGR under water stress was mostly associated with physiological adjustments rather than with differences in biomass allocation. P application maintained the balance of C metabolism in well-watered plants, but altered the proportion of nitrogenous compounds in N metabolism. By contrast, P application remarkably increased sucrose-metabolizing enzymes activities with an obvious decrease in sucrose content in water-stressed plants, suggesting an accelerated sucrose metabolism. Activation of nitrogen-metabolizing enzymes in water-stressed plants was attenuated after P application, thus slowing nitrate reduction and ammonium assimilation. P application hardly enlarged the phenotypic plasticity of dwarf bamboo in response to water in the short term. Generally, these examined traits of dwarf bamboo displayed weak or negligible responses to water-P interaction. In conclusion, P application could accelerate P(n) and sucrose metabolism and slow N metabolism in water-stressed dwarf bamboo, and as a result improved RGR and alleviated damage from soil water deficit., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

Denitrification and nitrate-ammonification are the responsible processes for nitrate removal in the estuaries. Temperature, nitrate and organic carbon availability are key factors controlling a rate of the nitrate reduction processes. This mixed cultures chemostat study investigates the competition ability and their nitrate reduction end-products of the bacteria isolated from an estuary at different temperatures. This study will help us to understand the seasonal nitrate reduction processes in an estuary. The experiments showed that a nitrate-ammonifier was the predominant process in the steady-state chemostat at high temperature. While a facultative denitrifier-nitrate ammonifier was the predominant process at low temperature. However, the main end products of nitrate reduction at high temperature were up to 61% N2 indicating a denitrifier still had an important role in the end products of nitrate reduction in the estuary. The data also showed that a nitrite respiring bacterium reduced nitrite to N2, that responsible for approximately 6-9% of total N2 produced in the culture. This study confirmed that nitrate ammonifiers out-compete denitrifiers at high temperature, however, denitrifiers still had an important role in end products of nitrate reduction. [ABSTRACT FROM AUTHOR]

The electrocatalytic production of ammonia has garnered considerable interest as a potentially sustainable technology for ammonia synthesis. Recently, non-metallic-doped materials have emerged as promising electrochemical catalysts for this purpose. This paper presents a comprehensive review of the latest research on non-metallic-doped materials for electrocatalytic ammonia production. Researchers have engineered a variety of materials, doped with non-metals such as nitrogen (N), boron (B), phosphorus (P), and sulfur (S), into different forms and structures to enhance their electrocatalytic activity and selectivity. A comparison among different non-metallic dopants reveals their distinct effects on the electrocatalytic performance for ammonia production. For instance, N-doping has shown enhanced activity owing to the introduction of nitrogen vacancies (NVs) and improved charge transfer kinetics. B-doping has demonstrated improved selectivity and stability, which is attributed to the formation of active sites and the suppression of competing reactions. P-doping has exhibited increased ammonia generation rates and Faradaic efficiencies, likely due to the modification of the electronic structure and surface properties. S-doping has shown potential for enhancing electrocatalytic performance, although further investigations are needed to elucidate the underlying mechanisms. These comparisons provide valuable insights for researchers to conduct in-depth studies focusing on specific non-metallic dopants, exploring their unique properties, and optimizing their performance for electrocatalytic ammonia production. However, we consider it a priority to provide insight into the recent progress made in non-metal-doped materials and their potential for enabling long-term and efficient electrochemical ammonia production. Additionally, this paper discusses the synthetic procedures used to produce non-metal-doped materials and highlights the advantages and disadvantages of each method. It also provides an in-depth analysis of the electrochemical performance of these materials, including their Faradaic efficiencies, ammonia yield rate, and selectivity. It examines the challenges and prospects of developing non-metallic-doped materials for electrocatalytic ammonia production and suggests future research directions. [ABSTRACT FROM AUTHOR]

Nitrate is one of the most widespread water contaminants globally. Nitrate levels in groundwater and surface water can rise to unhealthy levels as a result of nitrogen fertilizer runoff from lawns and farms. This research aims to selectively convert nitrate to gaseous nitrogen using Palladium‐Tin (Pd‐Sn) bimetallic electrodes electrodeposited on stainless‐steel (SS). Inductively coupled plasma optical emission spectrometry, scanning electron microscope, and X‐ray diffraction are used to analyze the composition, surface morphology, and crystal structure of the electrodes. The XRD analysis reveals that the Pd‐Sn/SS electrode has a crystalline nature when a Pd molar ratio >0.5 while an amorphous phase is detected over a Pd molar ratio (≤0.5). The electrochemical nitrate reduction is carried out in a 0.1 M HClO4 / 8 mM NaNO3 solution for 5 h using electrodes prepared in deep eutectic solvent (DES) system. The Pd0.93Sn0.07/SS electrode shows the best catalytic performance in terms of high nitrate conversion of 97%, N2 selectivity of 88%, and N2 yield of 86% compared to counter electrodes. These findings demonstrate a considerable impact of the electrode preparation process on nitrogen conversion, selectivity, and yield. [ABSTRACT FROM AUTHOR]

Unrestrained anthropogenic activities have severely disrupted the global natural nitrogen cycle, causing numerous energy and environmental issues. Electrocatalytic nitrogen transformation is a feasible and promising strategy for achieving a sustainable nitrogen economy. Synergistically combining multiple nitrogen reactions can realize efficient renewable energy storage and conversion, restore the global nitrogen balance, and remediate environmental crises. Here, we provide a unique aspect to discuss the intriguing nitrogen electrochemistry by linking three essential nitrogen‐containing compounds (i.e., N2, NH3, and NO3−) and integrating four essential electrochemical reactions, i.e., the nitrogen reduction reaction (N2RR), nitrogen oxidation reaction (N2OR), nitrate reduction reaction (NO3RR), and ammonia oxidation reaction (NH3OR). This minireview also summarizes the acquired knowledge of rational catalyst design and underlying reaction mechanisms for these interlinked nitrogen reactions. We further underscore the associated clean energy technologies and a sustainable nitrogen‐based economy. [ABSTRACT FROM AUTHOR]

Objective: To determine the optimal nitrogen dose combined with alfalfa in the growth, yield, and ion concentration in the sap of the lettuce leaf. Design/Methodology/Approach: We used a completely randomized experimental design, with a 2x5 factorial arrangement and nine repetitions in each treatment. The treatments consisted of five nitrogen doses (200, 250, 300, 350, and 400 kg ha-1) and two soil conditions (with and without alfalfa). Results: Aerial fresh weight (AFW), aerial dry weight (ADW), end-to-end diameter of the shoot (EDS), maximum diameter of the shoot (MDS), shoot weight (SW), and yield were higher when a 200-300 kg ha-1 dose of N was applied along with alfalfa. This application had a similar effect to the 300 kg dose of N ha-1, applied without the addition of alfalfa. The concentration of nitrates (NO3-) in the sap decreased with the addition of alfalfa and 200 kg of N ha-1. The concentration of potassium (K+) was higher with or without the addition of alfalfa and 250 kg of N ha-1. The concentration of calcium (Ca2+) was higher in the plants that received a 400-kg dose of N ha-1, whether alfalfa was included or not. Study Limitations/Implications: The lack of equipment prevented the determination of the nitrogen available in the soil. Findings/Conclusions: The incorporation of alfalfa into the soil is a good alternative to improve lettuce production and reduce the use of nitrogen fertilizers. [ABSTRACT FROM AUTHOR]

Nitrogen reduction reaction (NRR) and nitrate reduction reaction (NO3−RR) provide a potential sustainable route by which to produce ammonia, a next-generation energy carrier. Many studies have been conducted over the years, mainly emphasizing material design and strategies to improve catalytic performance. Despite significant achievements in material design and corresponding fundamental knowledge, the produced ammonia is still very limited, which makes it prone to bias. The presence of interferants (e.g., cations and sacrificial reagents), the pH of the solution, and improper analytical procedure can lead to the over or underestimation of ammonia quantification. Therefore, the selection of the appropriate ammonia quantification method, which meets the sample solution condition, along with the proper analytical procedures, is of great importance. In this review, the state-of-the-art ammonia quantification method is summarized, emphasizing the advantages, limitations, and practicality for NRR and NO3−RR studies. Fundamental knowledge of the quantification method is introduced. Perspective on the considerations for selecting the suitable quantification method and for performing the quantification process is also provided. Although non exhaustive, this focused review can be useful as a guide to design the experimental setup and procedure for more reliable ammonia quantification results. [ABSTRACT FROM AUTHOR]

The photocatalytic reduction of nitrate has received considerable attention due to its high efficiency and environmentally friendly nature. The excessive addition of hole scavengers is the most commonly used method to increase the nitrate reduction efficiency. However, achieving high selectivity in the photocatalytic reduction of nitrate to N 2 with low concentration of hole scavengers remains challenging. In this study, the SrFe x Ti 1−x O 3 /TiO 2 S-scheme heterojunction photocatalysts with many Lewis acidic adsorption sites have been developed. The experimental results demonstrated that the incorporation of 6% Fe into SrFe 0.06 Ti 0.94 O 3 /TiO 2 (SFTO6) resulted in the nitrate conversion rate of 97.68% and the N 2 selectivity reached 96.35% with 25 mmol/L formic acid. Moreover, it also exhibited excellent stability and recycle ability. After 5 cycles, SFTO6 still exhibited a stable photocatalytic denitration efficiency of 92.94%, highlighting its potential for practical application. Through comprehensive mechanistic investigations, enhancing direct reduction process is considered the key to its high reduction efficiency with low formic acid. And the Lewis acidic adsorption sites enhance N 2 selectivity by enriching NO x − on the surface of the material. Overall, this study provides a novel approach for achieving efficient photocatalytic reduction of nitrate to N 2 under conditions with low concentration of hole scavengers. [Display omitted] • The SrFe x Ti 1−x O 3/ TiO 2 catalyst with exceptional properties was synthesized for the purpose of photocatalytic denitrification. • The presence of abundant Lewis acidic sites promotes the N 2 selectivity. • The low dosage of formic acid highlights the actual application potential of the materials. [ABSTRACT FROM AUTHOR]

The nitrogen availability, that affects the greenhouse gas emission and the trophic level of lakes, is controlled mainly by microbial processes. We measured in a boreal nitrate and iron rich lake how the rates of potential denitrification and dissimilatory nitrate reduction to ammonia (DNRA) are affected by degradability of organic matter and availability of aqueous ferrous iron. We also investigated the microbial community by using 16S rRNA gene and shotgun metagenomic sequencing approach, which allows taxonomic analyses and detection of metagenome-assembled genomes (MAGs) containing genes for both nitrate reduction and iron oxidation. The results show that truncated denitrification, leading to release of nitrous oxide, is favored over dinitrogen production in conditions where the degradability of the organic matter is low. DNRA rates were always minor compared to denitrification and appeared to be independent of the degradability of organic carbon. Reduced iron stimulated nitrate reducing processes, although consistently only DNRA. However, the proportion of MAGs containing DNRA genes was low suggesting chemistry driven stimulation by reduced iron. Nevertheless, the metagenomic analyses revealed unique taxa genetically capable of oxidizing iron and reducing nitrate simultaneously. Overall, the results highlight the spatial variability in microbial community and nitrous oxide emissions in boreal lake sediments. [ABSTRACT FROM AUTHOR]

[Display omitted] Developing electrocatalysts for efficient reduction of nitrate contaminant to value-added ammonia as energy carrier is a pivotal part for restoring the nitrogen cycle. However, the selectivity of ammonia is far from satisfaction, often suffering from accumulation of toxic nitrite byproduct. Herein, a series of CuNi alloy nanoparticles embedded in nitrogen-doped carbon matrix (CuNi/NC) with hierarchical pores were fabricated by pyrolysis of bimetallic metal–organic frameworks (MOFs). The catalysts exhibited excellent selectivity (94.4%) and faradaic efficiency (79.6%) for nitrate reduction to ammonia, greatly outperforming the performance of monometallic Cu/NC (selectivity of 60.8% and faradaic efficiency of 60.6%). Impressively, the introduction of nickel distinctly suppressed the production of toxic byproduct of nitrite. Online differential electrochemical mass spectrometry (DEMS) and in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) tests were utilized to reveal the key intermediates and the reaction pathway. Density functional theory (DFT) calculations demonstrated that the introducing of nickel into copper lattice modified both the electronic and geometric structures of the catalysts. The copper and nickel sites in the CuNi alloy catalysts operate synergistically to facilitate the hydrogenation of NO 2 * to HNO 2 * and suppress the hydrogen evolution reaction, boosting the selective formation of ammonia. This work could provide a new synthetic route for bimetallic catalysts and mechanistic understanding for nitrate to ammonia reaction. [ABSTRACT FROM AUTHOR]

To find a method for efficient removal and conversion of inorganic nitrogen compounds in three reduction systems, which are the sponge iron (s-Fe0)，the sponge iron + biochar (s-Fe0/BC) micro-electrolysis system and the sponge iron + biochar + manganese sand (s-Fe0/BC/MS)-enhanced micro-electrolysis system, the studies have been completed on the conditions of different material ratios and initial pH. When the initial pH is 7, the nitrate removals reached to 7.6%, 61.5% and 80.3%, the nitrogen ratio of products reached to 5.8%, 22.4% and 38.3% respectively in s-Fe0, s-Fe0/BC (3:1) and s-Fe0/BC/MS (6:2:1) systems. The s-Fe0/BC/MS system was the best at nitrate removal over a wide pH range (2−12). At the same time, the nitrogen selectivity in the s-Fe0/BC/MS system was always better than that in other two systems. The X-ray photoelectron spectroscopy (XPS) results showed that the addition of manganese sand could enhance the ratio of Fe 3 O 4 in the sponge iron surface oxide, reduce the passivation of the sponge iron surface and accelerate the electron transfer rate. As a catalyst for the corrosion of sponge iron, manganese sand can increase the corrosion of sponge iron and enhance the micro-electrolysis role between iron and carbon. [Display omitted] • A micro-electrolysis system for enhanced nitrate removal was constructed. • The percentage of N 2 in the nitrate reaction products increased. • Addition of manganese sand accelerates the corrosion of sponge iron. • Manganese sand can effectively reduce the passivation of the sponge iron surface. [ABSTRACT FROM AUTHOR]

Catalysts prepared on ZrO2, Al2O3 and ZrO2–Al2O3 (ZrAl-10) supported with Anderson heteropolyanion (RhMo6) as active phase were investigated for the elimination of NO3− from water. Raman characterization of pure and supported RhMo6 phase showed the presence of polymolybdic species of different degrees of complexity when RhMo6 was supported. The temperature-programmed reduction study revealed the synergic effect between Rh and Mo species, through which the reducibility of Mo was promoted by Rh, and different phase/support interactions were verified. Among the supports, ZrAl-10 presented the highest acidity due to the presence of ZrO2 in the tetragonal modification and high specific surface area (due to Al2O3), favouring rhodium–molybdenum active phase/support interaction and high dispersion. All catalysts prepared were active in removing NO3−, the one prepared with the RhMo6 phase on the ZrAl-10 support being the most active. These results point to the formation of an active surface with a high dispersion of Rh and Mo. The highest selectivity to N2 (99.3) exhibited by the RhMo6/ZrAl-10 catalyst is proposed to be related to the high Rh dispersion (0.755) and to the presence of Lewis acid sites (oxygen vacancies) of the tetragonal ZrO2 modification that favour NO3− adsorption through electrostatic interactions. [ABSTRACT FROM AUTHOR]

Realizing the smallest nitrogen loss is a challenge in the nitrate reduction process. Dissimilatory nitrate reduction to ammonium (DNRA) and nitrate assimilation play crucial roles in nitrogen retention. In this study, the effects of the carbon source, C/N ratio, pH, and dissolved oxygen on the multiple nitrate reduction pathways conducted by Pseudomonas putida Y-9 are explored. Strain Y-9 efficiently removed nitrate (up to 89.79%) with glucose as the sole carbon source, and the nitrogen loss in this system was 15.43%. The total nitrogen decrease and ammonium accumulation at a C/N ratio of 9 were lower than that at 12 and higher than that at 15, respectively (P < 0.05). Besides, neutral and alkaline conditions (pH 7–9) favored nitrate reduction. Largest nitrate removal (81.78%) and minimum nitrogen loss (10.63%) were observed at pH 7. The nitrate removal and ammonium production efficiencies of strain Y-9 increased due to an increased shaking speed. The expression patterns of nirBD (the gene that controls nitrate assimilation and DNRA) in strain Y-9 were similar to ammonium patterns of the tested incubation conditions. In summary, the following conditions facilitated nitrate assimilation and DNRA by strain Y-9, while reducing the denitrification: glucose as the carbon source, a C/N ratio of 9, a pH of 7, and a shaking speed of 150 rpm. Under these conditions, nitrate removal was substantial, and nitrogen loss from the system was minimal. [ABSTRACT FROM AUTHOR]

Denitrification, anaerobic ammonium oxidation and dissimilatory nitrate reduction to ammonium (DNRA) are important microbial processes determining the fate of nitrogen (N) in estuaries. This study examined these processes in sediments of the York River Estuary, a tributary of Chesapeake Bay, and investigated environmental and microbial drivers of the rates of denitrification and DNRA. Nitrate reduction followed a consistent pattern throughout the year and across the estuary with nitrogen removal, primarily through denitrification, decreasing from the head of the estuary to the mouth and nitrogen retention, through DNRA, following the opposite pattern. At the mouth of the estuary, nitrogen retention was consistently higher than nitrogen removal. Denitrification rates showed strong linear relationships with concentrations of organic matter, nitrate and chlorophyll a , and the abundance of the nirS gene. DNRA rates were best correlated with the relative abundance of three bacterial families, Anaerolineaceae , Ectothiorhodospiraceae and Prolixibacteraceae , which carry the nrfA gene. The controls responsible for retention or removal of N from an estuary are complex, involving both geochemical and microbial factors. The N retained within estuaries may support primary production and seasonal algae blooms and result in estuarine eutrophication. [ABSTRACT FROM AUTHOR]

Rh is a promising electrocatalyst for the nitrogen reduction reaction (NRR) given its suitable nitrogen‐adsorption energy and low overpotential. However, the NRR pathway on Rh surfaces remains unknown. In this study, we employ surface‐enhanced infrared‐absorption spectroscopy (SEIRAS) and differential electrochemical mass spectrometry (DEMS) to study the reaction mechanism of NRR on Rh. N2Hx (0≤x≤2) is detected with a N=N stretching mode at ≈2020 cm−1 by SEIRAS and a signal at m/z=29 by DEMS. A new two‐step reaction pathway on Rh surfaces is proposed that involves an electrochemical process with a two‐electron transfer to form N2H2 and its subsequent decomposition in the electrolyte producing NH3. Our results also indicate that nitrate reduction and the NRR share the same reaction intermediate N2Hx. [ABSTRACT FROM AUTHOR]

To assess the contribution of reactive nitrogen from groundwater to surface waters, we need more knowledge on how reactive nitrogen behaves in the glacial till systems underlying many agricultural fields. Groundwater sampled from suction cups and piezometers placed in the glacial till underlying a winter wheat field shows the nitrate concentration in water leaching to deeper than 2 m below ground surface (mbg) is ~ 60 mg L−1. Within 5 mbg, all of the nitrate is removed and this appears to take place within a redox zone rather than at a sharp redox front. Ammonium released from the till is negligible. A 2D dataset reveals that the depth to the redox zone undulates between 3 and 5 mbg, perhaps a result of local variations in infiltration. It appears that the nitrate is generally reduced by the oxidation of pyrite and locally by organic matter in lenses within the till. [ABSTRACT FROM AUTHOR]

Highlights • Biochar amendment decreased soil NO 3 −-N leaching and soil nitrate reduction. • Biochar amendment promoted nitrate absorption and reduction by root. • Biochar affected plant NUE by modulating nitrate reduction of soil and root. • Biochar increased the NUE of M. hupehensis under decreasing the input of N fertilizer. Abstract A surplus of nitrogen (N) fertilizer can reduce plant nitrogen use efficiency (NUE), however, biochar can improve nutrient uptake by altering soil properties and root growth. Therefore, the objective was to determine how biochar alter soil nitrate (NO 3 −-N) availability and root development, and then to affect the plant NUE. The biochar was prepared by heating the apple branches at 700 °C and low oxygen. The effects of biochar on NO 3 −-N leaching and nitrogen oxides fluxes in orchard soil treated with five biochar rates (0, 0.5%, 1%, 2% and 4%) were investigated, the nitrate reduction in the soil and roots, and the NUE of Hupeh Crabapple (Malus hupehensis Rehd.) were measured in two soils amended (or not) with biochar, at six N fertilizer rates, using the solution culture, amino benzene sulfonate and subtraction method, respectively. The results showed that 0.5–4% (w/w) biochar decreased the leaching ratio of NO 3 −-N (9.9–68.7%) and nitrogen oxides flux (6.3–19.2%) in the soil. Soil denitrification intensity were most significantly decreased in the presence of 1% biochar when N fertilizer was applied at 0–450 mg NO 3 −-N kg−1; the soil nitrate reductase (NR) activity decreased at the application of 0–50 mg NO 3 −-N kg−1 in the presence of biochar, The root NR activity and root activity of M. hupehensis were significantly increased in the presence of 1% biochar at the application of 0–300 mg NO 3 −-N kg−1. In the biochar-amended soil, when the highest root activity and NR activity were obtained, N fertilizer application rate were reduced by 33.3% and 66.7%, compared to the non-amended soil, respectively. The NUE of M. hupehensis was increased by biochar-amended from 6.77% to 261.53%, comparied with the non-amended soils. These results indicated that biochar amendment could decrease nitrate leaching and nitrate reduction in soil, and promote nitrate absorption and reduction by root, thereby increasing the biomass and NUE of M. hupehensis when the input of N fertilizer was reduced from 450 to 300 mg NO 3 −-N kg−1. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Novel Cu 2 O-Cu0@Fe0 composite was synthesized and used for nitrate reduction. • The nitrate removal efficiency by Cu 2 O-Cu0@Fe0/HCOOH/UV system was 100%. • The N 2 selectivity of nitrate reduction by Cu 2 O-Cu0@Fe0/HCOOH/UV system was 95.4%. • Cu 2 O@Cu0-Fe0 composite can be used for nitrate removal from water and wastewater. Abstract The nitrate reduction by Fe-based materials has been extensively studied, however, the selectivity of nitrate reduction to nitrogen gas is very low, which hinders the application of this technology. In this study, a novel Cu 2 O-Cu0@Fe0 composite was synthesized and a strategy of Cu 2 O-Cu0@Fe0 composite combined with HCOOH under UV radiation as reducers for the nitrate reduction was established to improve the selective reduction of nitrate (NO 3 −) to nitrogen gas (N 2). The Cu 2 O-Cu0@Fe0 composite was synthesized by simple chemical replacement and O 2 oxidation process and characterized by SEM, EDS, XRD and XPS. The nitrate removal efficiency of 100% and the N 2 selectivity of 95.4% were achieved in Cu 2 O-Cu0@Fe0/HCOOH/UV system when the initial nitrate concentration was 50 mg N/L and the reduction time was 60 min. The nitrate reduction efficiency was low by the role of alone or combinations of Cu 2 O-Cu0@Fe0 composite, HCOOH or UV radiation. The quick reduction of nitrate to nitrite was due to the synergistic effect of electrons from the galvanic-type cell consisting of Fe0 as anode and Cu0 as cathode, photoelectrons from Cu 2 O under UV radiation and CO 2 − produced mainly via photochemical reaction between HCOOH and UV radiation. The subsequent conversion of nitrite to N 2 was caused by CO 2 −, which was responsible for the high efficient reduction of nitrate to nitrogen gas in the Cu 2 O-Cu0@Fe0/HCOOH/UV system. Finally, the denitrification mechanism of the Cu 2 O-Cu0@Fe0/HCOOH/UV system was tentatively proposed. [ABSTRACT FROM AUTHOR]

Estuaries are important nutrient filters between rivers and coastal zones. However, the quantification of the nutrient mitigation capacity related to benthic diagenesis is still poorly quantified. In this paper, we investigated carbon mineralization and the contribution of benthic nitrate reduction in two macrotidal eutrophic estuaries (Elorn and Aulne, Brittany, France) during winter and spring. These anthropized estuaries exhibited large variations of bottom water nitrate concentrations from very high values in upstream waters (up to 500 μM) to low values downstream (< 10 μM). Bottom water oxygen concentrations presented small gradients compared to nitrate concentrations gradients resulting in large variation in nitrate to oxygen ratios NO x − /O 2 between downstream and upstream (0.03–1.6). We combined the use of diagenesis modeling with field data (porosity, organic carbon and nitrogen, pore water profiles of dissolved oxygen, nitrogen, iron, manganese and sulfide concentrations, published in Khalil et al., 2013) and experimentally-determined nitrate reduction rates, in order to investigate the different organic carbon mineralization pathways in these estuarine sediments including denitrification and the contribution of benthic nitrate reduction to the estuarine N budget. Overall a good agreement between pore water data (organic carbon, oxygen, nitrate and ammonium) and model simulations was observed. The modeled organic matter mineralization rates were high in the upstream estuary and low in the saline estuary for the two estuaries Aulne and Elorn. This decrease may be related to the dilution and the trapping of allochtonous organic matter in estuarine sediments and its subsequent recycling in the upper estuary. Organic carbon mineralization rates were higher in the Elorn than in the Aulne estuary, which is most likely related to the labile character of the organic matter from urban origin exported from the Elorn watershed. The contribution of nitrate reduction to the total mineralization was generally high in upstream sediments (15–35%) of both Aulne and Elorn estuaries and decreased consistently downstream to 5–10%. The relative large contribution of nitrate reduction to organic matter degradation was to a large extent related to high bottom water nitrate concentrations that fueled 37–78% of total nitrate reduction in the upstream part of the estuaries. Overall, the reduction of bottom water nitrate by denitrification to N 2 represented 3–13% of the river flux of nitrate in these estuaries in winter and spring, and could reach ~ 50% during summer. These results highlight that nitrate reduction in the sediment attenuate the high river nitrate flux, despite the huge quantities of anthropogenic nitrate discharged by the two rivers to the estuaries. [ABSTRACT FROM AUTHOR]

Denitrifying woodchip bioreactors offer an opportunity to intercept and reduce nitrogen loads between agricultural fields and downstream aquatic ecosystems. Here we assessed the performance of three in-drain bioreactor beds installed in open drains receiving runoff and shallow ground water from rain-fed sugarcane production in the Wet Tropics of Australia. Drain nitrate-N concentrations were generally low, with a mean of 0.2 mg L−1 and maximum of 3.3 mg L−1, which may have been partially due to denitrification in the contributing soils. Bioreactors reduced the concentration of nitrate-N in intercepted waters (average 41% reduction). However, removal rates were often limited by nitrate-N availability. Load reduction over the 2018/19 season was just 0.11 kg N ha−1 yr−1. This limited performance was in large part due to the dynamic nature of nitrogen loads in this system. Specifically, a high proportion of the annual nitrogen load occurring during 'first-flush' events immediately after fertilization (i.e. 72% during a 10-day period in 2018/19) resulting in considerable bypass flow (i.e. low interception). Our study is the first in the Australian Wet Tropics to assess the annualized performance and total load reductions of in-drain denitrifying bioreactor beds. Although showing their potential, our results highlight the fact that denitrifying bioreactor performance is determined by the hydraulic context of the catchment, and the proportion of the annual nitrate load that can be successfully intercepted. [ABSTRACT FROM AUTHOR]

Cu and Pd–Cu (Pd = 40 wt%) electrodes supported on stainless steel (Cu/SS and Pd–Cu/SS) were prepared using electrodeposition methods and characterized by X-ray diffraction, scanning electron microscope, and X-ray photoelectron spectroscopy. The electrocatalytic reduction of nitrate on Cu/SS and Pd–Cu/SS electrodes was studied in sodium perchlorate electrolyte. By tuning the applied potential, nitrate was found to be selectively reduced to different products, indicating a strong dependence of nitrate reduction reaction on the applied potential. Moreover, the effect of electrode material on nitrate reduction was studied also. Results showed that the nitrate reduction over the two electrodes was different due in part to distinct surface morphology. Results demonstrated a novel avenue to improve the selectivity of nitrate reduction products through controlling the applied potential and selection of electrode material. Results also showed strategy warrant further studies on nitrate conversion to harmless nitrogen gas. [ABSTRACT FROM AUTHOR]

Nitrate is an important nitrogen source for organism, but whether and how nitrate improves poly-γ-glutamic acid (γ-PGA) production of bacterial is not clear. The effect of nitrate on γ-PGA production of Bacillus licheniformis WX-02 was investigated. By addition of 50 mmol/L nitrate, the γ-PGA yield reached 12.3 ± 0.21 g/L, which increased 2.3-fold compared to the control. The mechanism of enhanced γ-PGA production was further investigated by analysis of nitrate reduction, physiology, pyruvate overflow metabolism and energy synthesis. Nitrate reduction was only carried out in the middle stage of γ-PGA fermentation. The result of consumption of nutrients showed that glucose uptake was not effected and the l-glutamic acid utilization efficiency increased from 48.3 to 77.0 %. The date of overflow metabolism obtained from high-performance liquid chromatography showed that the metabolism of pyruvate, formate, lactate and acetoin was both heightened by nitrate reduction, while the 2,3-butanediol biosynthesis was decreased. Meanwhile, the change of energy indicated that more ATP was synthesized during nitrate reduction. In summary, nitrate was a positive effector of γ-PGA biosynthesis in B. licheniformis WX-02 and nitrate reduction affected multi-metabolism pathways, including glycolysis, overflow metabolism and energy metabolism. [ABSTRACT FROM AUTHOR]

Highlights: [•] Pt/SrTiO3:Rh–SnPd/Al2O3 system promoted photocatalytic reduction of NO3 − in water. [•] Pt/SrTiO3:Rh–SnPd/Al2O3 system was superior in activity and selectivity to SnPd/SrTiO3:Rh. [•] Selectivity to N2 was 94% under the optimum reaction conditions. [•] H2, H2CO, and HCOOH formed on Pt/SrTiO3:Rh acted as reductants for NO3 − over SnPd/Al2O3. [ABSTRACT FROM AUTHOR]

[Display omitted] • Uniform composition-controlled Cu x Pd 100-x alloy NWs are prepared for NO 3 RR. • Cu 28 Pd 72 NWs deliver an unprecedented N 2 selectivity of 75.9 ± 5.2% in product. • N 2 formation is kinetically favored via a pathway of NO 2 * → NO* → N* → N 2 * on Pd. • Contiguous surface Pd ensemble with specific size is the key to high N 2 selectivity. • Cu serves to initiate NO 3 ––NO 2 * conversion and lower H ads coverage on Pd ensemble. Selective electrocatalytic nitrate reduction reaction (NO 3 RR) to dinitrogen (N 2) is essential to nitrogen-cycle management and environmental sustainability. Palladium-based nanomaterials were extensively studied as NO 3 RR catalysts, but only delivered limited N 2 selectivity (<50%, NH 3 dominated the product). Here we report that, by tuning bimetallic composition of CuPd alloy nanowires, the Cu 28 Pd 72 nanowires deliver a near-unit conversion of NO 3 –-N and an unprecedented N 2 product selectivity of 75.9 ± 5.2% in treating 22.5 mg L−1 NO 3 –-N solution at −0.80 V vs. Ag/AgCl. Combining in-situ spectrometric measurements and theoretical calculations, we demonstrate that the contiguous Pd ensemble with a specific size at catalyst surface is essential to the N 2 formation via a kinetically-favored pathway of NO 2 * → NO* → N* → N 2 *. Alloying Pd with Cu is indispensable as Cu contributes to the N*-N* pairing by initiating the NO 3 ––NO 2 * conversion and lowering the H ads coverage on catalyst. This work discloses the key surface atomic structure for N 2 formation, and provides a guideline for the design of efficient NO 3 RR catalyst that enables selective NO 3 ––N 2 conversion. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electron-deficient Cuδ+ is stabilized at the Cu-Al 2 O 3 interface via Cu–O-Al bond. • The Cuδ+ is highly active and durable in selective conversion of NO 3 – to NH 3. • Strong binding of Cuδ+ with N-intermediates accounts for high activity/selectivity. • The Cuδ+ keeps efficient in converting the concentrated nitrate to NH 3. • The NH 3 can be eliminated with an anode-driven breakpoint chlorination reaction. Electrocatalytic nitrate reduction to NH 3 not only enables the recycling of nutrients from nitrate wastewater but can also lead to complete nitrogen elimination when paired with an NH 3 oxidation reaction to achieve innocuous N 2. Albeit electron-deficient copper (Cuδ+) is an active catalytic site for an electrocatalytic nitrate reduction reaction (ENRR), its stabilization under the reductive polarization potential of ENRR is challenging. Herein, we report the in-situ electroreduction of CuAl-mixed oxide to construct a Cu-Al 2 O 3 interface with strong metal-support interactions (CuAl-LDO-r), which can form and stabilize Cuδ+ via Cu–O-Al bonds. The batch ENRR tests revealed that Cu 52 Al 48 -LDO-r delivers an NH 3 -N selectivity of 97.4%, stable specific activity of 661.6 mg-N m-2h−1 for NH 3 -N production (faradaic current efficiency of 70.4%), and minimal Cu leaching when reducing 22.5 mg L-1 NO 3 –-N at −1.10 V vs. Ag/AgCl, outperforming most of the reported catalysts under similar reaction conditions. Combined in-situ spectrometric analyses and theoretical calculations demonstrate that the robust performance of Cuδ+ originates from its substantial affinity toward the N-intermediates, which promotes molecule activation and prevents intercoupling to dinitrogen species. For nitrate elimination, the ENRR was coupled with an anode-driven breakpoint chlorination reaction, and the designed system enabled complete conversion of NO 3 –-N (44.5 mg L-1) to N 2 with an electrical consumption of 1.82 kwh mol N -1. [ABSTRACT FROM AUTHOR]

[Display omitted] • A two-step method was used to remove NO 3 –-N from aqueous solution under wide pH range. • 100% NO 3 –-N removal efficiency was obtained at pH 7 using Al/Cu bimetal reduction as the first step. • Satisfied NO 3 –-N reduction performance was achieved by Al/Cu under varies pH condition. • 100% N 2 conversion rate was further obtained with the second step using sulfamic acid as reductant. To expand the working pH range of NO 3 –-N reduction from aqueous solution, a two-step method including the Al/Cu bimetal and sulfamic acid reduction was developed. In this process, Al/Cu bimetallic materials were prepared by chemical deposition method and characterized by EDS, SEM, XRD and XPS. The NO 3 –-N reduction batch experiment showed that 100% of NO 3 –-N was reduced and converted to N 2 at pH of 7, Al/Cu dosage of 30 g/L and EDTA-2Na concentration of 6 mmol/L. When the pH value was adjusted to 3, 5 and 9, NO 3 –-N reduction efficiencies ca. 80–97% were also obtained in the first step, and 100% N 2 selectivity was further obtained with the second reduction step at pH of 3, 7 and 9. The kinetics study indicated that the Al/Cu reduction process was in accordance with the pseudo-second order kinetics model. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Z-scheme heterojunction accelerated the separation of electron-hole pairs. • The doping rGO can enhance the electron's enrichment. • The chloramphenicol and Cr (VI) can be removed simultaneously and effectively. • The nitrate nitrogen has been reduced into ammonia nitrogen. The simultaneous elimination of organic pollutant and heavy metals using efficient catalysts has attracted much attentions, but facing obstacles of low redox ability and high recombination rate of photogenerated carriers. Herein, we have successfully synthesized Bi 2 SeO 5 /rGO/MIL-88A composition for the synergistic photocatalytic removal of chloramphenicol (CAP) and Cr6+. The optimal sample can concurrently remove 85.68% of CAP and 91.85% of Cr6+ in 120 min. The enhanced performance is attributed to that Z-scheme heterojunction formed between metal compounds, which accelerates the separation of electrons and holes. Notably, the hybrid of rGO is proved to facilitate the flow of electrons and significantly inspire the nitrogen reduction (59.34% of N is reduced into ammonia). Furthermore, the mineralization and denitrification pathway of CAP are proposed based on calculation and experiment. Our study integrates reduction, degradation and denitrification innovatively, providing a new insight for simultaneous removal of heavy metal and nitrogenous organic pollutant. [ABSTRACT FROM AUTHOR]

The root/shoot-ratio is a simple parameter to describe the systemic response of plants to alterations of their nutritional status, as indicated by the C/N-balance of leaves. The ‘functional equilibrium hypothesis’ holds that leaf growth is limited by the supply of nitrogen from the roots, whereas root growth depends on the carbon supply from leaves. The nature of the systemic control that balances root and shoot growth is not fully understood. Previous experiments have shown that root growth of transformed tobacco plants, which lack functional root nitrate reductase, was severely impeded, when plants were grown on NO as the sole N-source. In these experiments, the root/shoot-ratio was correlated with the Glutamate/Glutamine-ratio of roots. In the present study we tested the hypothesis that high internal Glu contents (in relation to Gln) inhibit root growth. Wild type and transformed tobacco plants were given access to both NH4 and NO3, and were cultivated at ambient and elevated pCO2 in order to vary carbon availability. The uptake and assimilation of NH by the root was significantly higher in transformed than in wild type tobacco, in particular at elevated pCO2. Consequently, the Glu/Gln-ratio in the root of transformants was significantly lower than in NO -grown plants, and was, in the present study, not different from the wild type. However, we failed to observe a correlation between plant architecture and the Glu/Gln-ratio of roots, suggesting that signals arising from the immediate products of nitrate reduction (nitrite) are involved in the systemic control of root growth. Furthermore the synthesis of root-derived signals, which affect N-turnover, starch re-mobilization and the growth of leaves, appears to be associated with root nitrate reduction. This enzymatic step seems to be indispensable for the systemic control of biomass partitioning, and plays a crucial role for the integration of carbon and nitrogen metabolism at the whole plant level. [ABSTRACT FROM AUTHOR]

Boron (B) toxicity has become important in areas close to the Mediterranean Sea where intensive agriculture has been developed. The objective of this research was to study the effects of B toxicity (0.5 mm and 2.0 mm B) on nitrogen (N) assimilation of two tomato cultivars that are often used in these areas. Leaf biomass, relative leaf growth rate (RGRL), concentration of B, nitrate (NO3−), ammonium (NH4+), organic N, amino acids and soluble proteins, as well as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthase (GS), glutamate synthetase (GOGAT) and glutamate dehydrogenase (GDH) activities were analysed in leaves. Boron toxicity significantly decreased leaf biomass, RGRL, organic N, soluble proteins, and NR and NiR activities. The lowest NO3− and NH4+ concentration in leaves was recorded when plants were supplied with 2.0 mm B in the root medium. Total B, amino acids, activities of GS, GOGAT and GDH increased under B toxicity. Data from the present study prove that B toxicity causes inhibition of NO3− reduction and increases NH4+ assimilation in tomato plants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe0 NPs show promising in NO 3 –-N pollution abatement; • Single Fe0 favors the conversion of NO 3 –-N to NH 3 -N rather than N 2 -N; • Poor N 2 yield results from the over-strong binding of H* and N-intermediates with Fe0; • Pd decoration tunes the nFe0-N-intermediate binding strength, promoting the N 2 yield. Nitrate (NO 3 –) removal on nanoscale zero-valent iron-based nanoparticles (nFe0 particles) represents one efficient and green technology for nitrate pollution abatement, but its development is hindered by the low product selectivity towards harmless N 2. Herein we demonstrate the inferior performance of nFe0 in N 2 production originates from its over-strong affinity with both the H* and the N-intermediates (denoted as N*), leading to a low N/H molar ratio and a poor mobility of N* on Fe surface that facilitates the formation of NH 3 rather than N 2. Increasing NO 3 – feeding concentration or lowing nFe0 dose can uplift the N 2 selectivity up to 41.9% (vs. 19.3% by single nFe0 in removing 20 mg L-1 NO 3 –-N), but has to sacrifice NO 3 – removal efficiency and yield more toxic NO 2 –. The nFe0 surface modification by 12.0 wt% palladium (Pd) gives rise to a N 2 selectivity of 46.0% and a NO 3 – removal efficiency above 90% (vs. 100% by single nFe0). Theoretical calculations reveal the critical role of Pd in weakening the binding strengths of H* and N* on catalyst, which enables to reduce the H* adsorption and promote the migration of N* that increases the N*-N* encountering possibility for N 2 formation. This correlation between surface chemistry and NO 3 – conversion may guide the design of improved Fe0-based materials for practical nitrate remediation. [ABSTRACT FROM AUTHOR]

Nitrate and its metabolites as common pollutants in water had attracted widespread attentions. Converting nitrate to nontoxic and harmless nitrogen via photocatalysis was a promising approach. In this study, a novel Z-scheme NH 2 -MIL-101(Fe)/BiVO 4 heterojunction was successfully prepared. As-prepared Z-scheme heterojunction along with built-in electric field facilitated the charge separation and enhanced the photocatalytic activity in nitrate reduction. The results showed that 0.10-MBiVO photocatalyst exhibited the highest nitrate removal rate of 94.8% (initial concentration 100 mgN/L) and final selectivity to N 2 of 93.4% in 50 min under ultraviolet irradiation. Moreover, formic acid was proved as better hole scavenger compared with methanol and oxalic acid. And the concentration of formic acid had significant influence on the process of nitrate photocatalytic reduction. 0.10-MBiVO photocatalyst exhibited excellent reusability in the recycling tests, indicating its great potential in practical application of nitrate photocatalytic removal. The mechanism of the enhancement as well as reaction pathways for nitrate photocatalytic reduction on NH 2 -MIL-101(Fe)/BiVO 4 were comprehensively explored and described at the end. [Display omitted] • Novel Z-scheme NH 2 -MIL-101(Fe)/BiVO 4 heterojunction was synthesized. • 0.10-MBiVO photocatalyst exhibited the highest nitrate removal rate. • Mechanism of the enhancement has been explored and discussed. • The possible reaction pathway has been proposed. [ABSTRACT FROM AUTHOR]

A novel biochar electrode Bio-Fe 3 O 4 /CF used for electroreduction of nitrate was prepared by the hydrothermal synthesis method. The results showed that the growth of spherical Fe 3 O 4 on the surface of smooth biochar can significantly increase the nitrate reduction rate. Besides, the presence of Cl and Br in the solution could promote the conversion of NH 4 + to N 2 , thereby regulating the element nitrogen in the solution. Mechanistic analysis showed that the interconversion of Fe (II) and Fe (III) facilitates the transfer of electrons to nitrate. This study not only provides a biochar electrode material for the efficient removal of nitrate but also simply reveals regulation of halogen in solution, which provides a particular theoretical and data basis for nitrate removal. [Display omitted] • A novel electrode was prepared by biochar and Fe 3 O 4 for nitrate reduction. • The application of this electrode is beneficial to nitrate purification in water. • Interconversion of Fe (II) and Fe (III) facilitates electron transfer. • The presence of Cl and Br could regulate the form of nitrogen in the solution. [ABSTRACT FROM AUTHOR]

Selective electrocatalytic conversion of NO 3 – to N 2 is an environmental-friendly strategy to close the anthropogenic nitrogen-based cycle. This work reported a metal-organic framework-derived electrocatalyst with earth-abundant bimetallic sites, showing quantitative (~97.9% conversion) and selective (~99.3%) nitrate-to-N 2 transformation. More importantly, both post-catalysis concentrations of NO 3 – and NO 2 – meet the drinking water limit requirements, set by World Health Organization. The reaction intermediates and mechanistic pathways in electrocatalytic reduction of NO 3 – to N 2 are elucidated by a variety of in-situ experimental studies and DFT calculations. The enhanced and selective electrocatalytic performances are ascribed to the relay catalytic effects of the neighboring Fe-Ni catalytic sites residing in the porous carbon electrocatalysts, which are structurally determined by X-ray absorption spectroscopy (XAS) as well as calculated structural model, with Fe sites decreasing the reaction barrier for NO 3 – conversion and Ni centers facilitating the adsorption and activation of reaction intermediates (NO 2 –, NO* and N 2 O*). [Display omitted] • A MOF-derived electrocatalyst with Fe-Ni-N 6 coordination centers are synthesized. • The relay catalytic effects of the Fe-Ni catalytic sites accelerate the reaction. • The electrocatalyst exhibits 97.9% nitrate removal rate and 99.3% N 2 selectivity. • The post-catalysis concentrations of NO 3 – and NO 2 – meet the limit requirements. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spatially confined reduction route for fabricating composite indium-based catalyst. • Abundant active sites and hybrid electronic structure give high catalytic activity. • Remarkable nitrate reduction activity with high ammonia yield rate can be achieved. • Detailed specification of reduction pathway was demonstrated by DFT calculations. Nitrate contaminant in groundwater has become a global problem. As a nitrogen-containing source, catalyzing nitrate to ammonia by electrochemical conversion draws promising blueprint from the perspective of solving energy crisis and environment pollution. Here we report a sulfur doped graphene with indium confined for nitrate reduction. The catalyst exhibits an ammonia production of 220 mmol g cat -1h−1 and a Faradaic efficiency of about 75% at −0.5 V vs reversible hydrogen electrode (RHE). The experimental results combined with density functional theory (DFT) calculations demonstrate that the abundant active sites afforded by S doped graphene and hybrid electronic structure of In species in catalyst account for predominant nitrate reduction and suppression of hydrogen evolution reaction. This work can offer an electronic structure design strategy for other energy related applications. [ABSTRACT FROM AUTHOR]