Nitrate Accumulation Research Articles

Enhanced nitrogen removal in mainstream deammonification systems at ambient temperature by novel modified carriers and differentiation of microbial community transformation

Zeolite-modified polyurethane (ZP) carriers and zeolite/tourmaline-modified polyurethane (ZTP) carriers were proposed to enhance mainstream deammonification. The system with ZTP carriers was rapidly established in 28 days with a nitrogen removal rate (NRR) of 0.150 kg N·(m3·d)−1. Moreover, the facilitative effect of tourmaline was suggested by the highest humic acid peak intensity and more balanced potential activity. Besides, SEM-EDS analysis revealed carrier characteristic improvement was achieved in both novel carriers while maintaining an excellent spatial structure. Moreover, the microbial analysis suggested that both modified carriers support the substrate supply to anaerobic ammonium oxidizing bacteria (AnAOB) by enhancing dissimilatory nitrate reduction to ammonium and partial denitrification under nitrate accumulation conditions. Nevertheless, the ZTP system had a greater advantage over maintaining the original AnAOB (Candidatus Jettenia) and ammonium oxidizing bacteria (Nitrosomonas) abundance. Overall, this study provides ZTP carriers with great potential for facilitating the establishment of mainstream deammonification at full-scale WWTPs.

Survival strategies of Nitrospira in a stable nitritation-denitritation system treating low-strength fermented wastewater

Mainstream nitritation and denitritation can save aeration energy and carbon sources, but it is difficult to eliminate nitrite-oxidizing bacteria. Except for nitrite oxidation, Nitrospira may benefit from mixotrophic lifestyles. In our previous study, stable NOB suppression was achieved in a multi-cycle sequencing batch reactor (MCSBR) treating fermented low-strength wastewater. However, abundant Nitrospira was always detected, which was contrary to the negligible nitrate accumulation. Batch tests indicated that only acetate could be consumed by the enriched Nitrospira within six hours. In another batch test within six days, nitrate was fully or partially denitrified to nitrite after adding formate or acetate, while Nitrospira decreased 86.5 % and 28.7 % respectively. After adding formate, two hydrogenotrophic denitrifiers Hydrogenophaga and Methyloversatilis highly proliferated, but only Hydrogenophaga was also found in the MCSBR. Therefore, Nitrospira might still grow through nitrite oxidation, while the generated nitrate was timely reduced by Hydrogenophaga in the presence of simple organic carbons, or directly survived by heterotrophic acetate metabolism.

NITRATE CONTENT IN VEGETABLES IN WATER-INRATED WATER BODIES OF THE NORTHERN AND INGULETSKY GOK

The content of nitrates in vegetables is a rather urgent problem and is of interest to structures that control and regulate the possible consequences of an excessive amount of nitrates for human health. The main causes and features of food pollution are shown: irrigation of fields with water containing wastewater from industrial enterprises, excessive and uncontrolled use of fertilizers, conditions for growing vegetables and seasonality.The process of environmental pollution with nitrates, in particular, surface water resources, is considered. An analysis of the suitability of surface water for irrigation was carried out near the villages of Andreevka, Shevchenkovskoye, Zavyalovka, Annensky quarry and Ternovsky district of Krivoy Rog and showed that the content of nitrates does not exceed the MPC. The reasons for the accumulation of nitrates in plant products are shown. The transformations of nitrate ions and their toxic effect on the human body are given. The paper also outlines the main ways to reduce the content of nitrates in crop production. A quantitative analysis of nitrate ions in vegetable raw materials in the spring-autumn period was carried out: cucumbers, cabbage, potatoes, tomatoes, carrots and onions by the iodometric method, the express method based on the use of a diphenylamine reagent and the express method. method using the GreenTest nitrate tester, grown on the territory near such enterprises as the Northern and Ingulets GOK. The content of nitrates exceeds MPC in early potatoes and tomatoes.

Research Progress on Cu-Based Catalysts for Electrochemical Nitrate Reduction Reaction to Ammonia

Since the conventional Haber-Bosch ammonia synthesis loop suffers from harsh process conditions, high energy consumption, and heavy pollution, the artificial catalytic synthetic NH3 has emerged as a promising alternative method for producing NH3. Meanwhile, nitrate (NO3–) accumulation in the environment causes serious problems involving health and environmental issues. The urgent need to eliminate NO3– and produce NH3 perfectly caters to the NO3– reduction reaction (NO3RR) via an attractive electrocatalytic route. Cu-based catalysts exhibit an inhibiting effect on hydrogen evolution, rapid reduction kinetics, and stable catalytic performance, revealing remarkable advantages for NO3RR. In this review, we summarize the recent achievements of Cu-based catalysts in electrocatalytic NO3RR, discuss the detection methods for evaluating NO3RR performance, and introduce the fundamentals for understanding the thermodynamics and kinetics. This review can provide guidance and help for the rational design and development of non-noble metal catalysts in electrocatalytic NO3RR to NH3.

Agronomic and environmental benefits of ‘re-using’ a biodegradable mulching film for two consecutive lettuce cycles

Biodegradable films are a valuable and sustainable alternative to plastic films for mulching soils since they avoid the environmental and economic problems related to plastic removal and disposal. Nevertheless, the fast degradation of such materials could make them unsuitable for mid- to long-term use. In a field experiment, the agronomic performance of a biodegradable mulching film (MB) was compared to that of conventional low-density polyethylene (LDPE) film for two consecutive lettuce cycles (winter and spring). In the conditions of this trial, MB showed good resistance to atmospheric agents, with a reduction of its integrity and mechanical properties only after six months. The effects on soil temperature and lettuce yield did not differ from those obtained with LDPE films. The effect on harvest timing was the same as that with LDPE in the spring cycle, while in the winter cycle, the harvest was delayed by about five days compared to LDPE. Mulching films reduced nitrate accumulation in leaves mainly during the winter cycle. However, the effect needs to be further explored with experiments in different pedoclimatic conditions that consider the effects of mulching on nitrification and nitrate-reductase activity that could be affected by changes in soil temperature and moisture. Highlights - Biodegradable mulching films (MB) showed good mechanical resistance in the medium-long term (2 consecutive lettuce cycles). - Decrease in integrity and resistance to tearing became significant after 150-170 days. - The effect of MB on lettuce yield quantity and quality was comparable with that using low-density polyethylene (LDPE) films. - The effects of both mulching films on leaf nitrate content need further research in different pedoclimatic conditions. - MB can be recommended since it reduces the economic and environmental costs of removal and disposal of LDPE films.

Patterns of long-term variations of nitrate concentration – Stream discharge relationships for a drained agricultural watershed in Mid-western USA

Nitrate Concentration–discharge (C-Q) relationshipshave been used to infer nitrate sources, storage, reactions, and transport in watersheds, and to reveal key processes that control runoff chemistry. Yet, studies on long-term nitrate C-Q relationships are limited due to scarce high frequency (e.g., daily) concentration data. In this paper, using a long-term high-frequency dataset (1976–2019) comprising stream flow and nitrate concentrations, we quantitatively analyzed the long-term variations of event-scale hysteresis patterns (quantified by hysteresis index, HI, and flushing index, FI) to infer the leaching mechanisms of nitrate in an artificially drained agricultural watershed in Mid-western U.S. Our results revealed that most events exhibited anti-clockwise behaviors (HI < 0), regardless of whether nitrate was flushed or diluted during events. This means that water with high levels of nitrate-N reaches the stream network slower than water with lower nitrate concentrations. Long-term mean FI was close to zero but had strong seasonal patterns with dilution patterns observed during Winter and Summer, and flushing patterns during late Spring and Fall. The consistently negative HI values regardless of the FI value gave a strong indication of the preponderant role of the near-drain zone that usually exhibits accelerated leaching and less accumulation of nitrate in the soil profile in these drained agricultural watersheds. Both HI and FI depicted strong but opposite seasonality because of weather patterns and agricultural activities, particularly N fertilization. Overall, our findings suggest a little evidence of the role of deep groundwater and instead a strong evidence of the role of subsurface drainage as the primary pathway for nitrate transport in drained agricultural watersheds. Therefore, artificial drainage could dampen N legacy caused by the historically intensive N fertilization in drained agricultural landscapes.

Biochar-based molybdenum slow-release fertilizer enhances nitrogen assimilation in Chinese flowering cabbage (Brassica parachinensis).

Low molybdenum (Mo) bioavailability in acidic soil obstructs vegetable nitrogen assimilation and thus increases the health risk of vegetable ingestion due to nitrate accumulation. Constantly providing available Mo in acidic soil is a challenge for decreasing nitrate accumulation in vegetables. In this study, three Mo application methods, including biochar-based Mo slow-release fertilizer (Mo-biochar), seed dressing, and basal application, were investigated to enhance Mo bioavailability in acidic soil and nitrogen assimilation in Chinese flowering cabbage (Brassica parachinensis). The results showed that Mo-biochar constantly and sufficiently supplied Mo nutrients throughout the growing period of Brassica parachinensis, as evidenced by the soil available Mo, plant Mo uptake, and Mo values. The improved Mo supply was attributed to the alleviation of acidic soil (pH from 5.10 to 6.99) and the slow release of Mo adsorbed on biochar. Mo-biochar increased the nitrate reductase (NR) activity by 238.6% and glutamate dehydrogenase activity by 27.5%, indicating an enhancement of the rate-limiting steps of nitrogen assimilation, especially for nitrate reduction and amino acid synthesis. The increase in Mo-containing NR could be directly ascribed to the high level of Mo in Brassica parachinensis. Compared with the control, the nitrate content of Brassica parachinensis decreased by 42.9% due to the nitrate reduction induced by increased NR. Additionally, Mo-biochar was beneficial to vegetable growth and quality. In contrast, the transformation from NO3- to NH4+ was blocked with Mo seed dressing and basal application because of low Mo bioavailability in the soil, resulting in a high nitrate content in Brassica parachinensis. Conclusively, Mo-biochar can slowly release Mo and improve the neutral environment for Mo bioavailability, which is an effective strategy to mitigate the high nitrate accumulation of vegetables planted in acidic soil.

Nitrate transport behavior behind subsurface dams under varying hydrological conditions.

The construction of subsurface dams for controlling seawater intrusion triggers the accumulation of nitrate upstream of a dam. This is raising the concerns about nitrate contamination in those regions of coastal aquifers that are supposed to be used as a fresh groundwater source behind a subsurface dam. Research on this subject has been mostly restricted to the use of a simplified sea boundary (e.g., static and no slope), ignoring sea level fluctuations driven by tides. In this study, the combined effect of tides and subsurface dams on nitrate pollution in upstream groundwater was examined through laboratory experiments and numerical simulations. The results revealed that the difference in the extent of nitrate contamination under various conditions (i.e., static, tidal, static with a dam, and tidal with a dam) was related to the temporal pollution behavior. In the early stage, nitrate contamination in upstream groundwater was essentially identical for different scenarios. Both tides and subsurface dams were found to increase nitrate contamination in upstream aquifers. The extent of nitrate contamination increased with higher tidal amplitudes, whereas the increment was more evident for a large tidal amplitude. The effects of tides and subsurface dams on nitrate contamination were also regulated by the locations and infiltration rates of the pollution source. Interestingly, under the joint action of tides and subsurface dams, the increment in the extent of nitrate pollution was greater than the sum of their individual effects. The increased pollutions caused by subsurface dams and tides were quantified as 9.47% and 37.22%, respectively, whereas the increased value caused by their joint action was measured as 51.10%. These findings suggest that tidal activity should not be overlooked when assessing nitrate contamination in upstream groundwater.

Agricultural practices regulate the seasonality of groundwater-river nitrogen exchanges

Soil System Budgets (SSB) of nutrients are generally performed annually over arable land to infer their use efficiency and water pollution risk in highly exploited agricultural watersheds. They are seldom partitioned into seasonal budgets and matched with seasonal nutrient transport in adjacent river reaches. We calculated seasonal soil nitrogen (N) budgets in a Mincio River sub-basin (Italy), and we analyzed the dissolved inorganic N net export in the river reach draining such sub-basin. Our results show seasonal differences of SSB with N excess in winter and even more in spring, equilibrium among sources and sinks during autumn and N deficit during summer. Seasonal inorganic N loads transported by the river were not correlated with SSB as they peaked in late summer and were at their minimum in early spring. Fertilization uncoupled to significant uptake supports N excess in winter and spring, whereas crop uptake uncoupled to N inputs supports summer N deficit. Nitrification cannot explain nitrate accumulation in the river reach, suggesting alternative dynamics driving the local hydrology. Flood irrigation results in large soil nitrate solubilization, transport and in upward migration of the groundwater piezometric head during spring and summer periods. River water is likely replaced by nitrate-rich groundwater when the groundwater recharge exceeds a certain threshold coinciding with late summer. Irrigation is then interrupted and the piezometric head, together with nitrate exchange, decreases. This work suggests that a deep understanding of N dynamics in agricultural watersheds with flooding irrigation on permeable soils needs the reconstruction of the vertical pathways of nitrate and of river-groundwater interactions. Moreover, the partitioning of annual into seasonal N budgets and their combination with irrigation practices allows the identification of hot moments in N cycling. Agricultural practices minimizing nitrate excess, its mobility and the risk of surface and groundwater pollution are suggested for this area.

Identifying multivariate controls of water and nitrate in deep loess deposits under different land use types

Identifying the environmental factors controlling deep soil water and nitrate is important for the sustainability of vegetation and ecosystems. However, the combined effects of multiple factors at varying scales have been poorly understood, especially in those regions with thick vadose zones and deep-rooted plants. The aim of this study is to identify the multivariate controls of water and nitrate in seven > 13 m deep boreholes under different land use types on China’s Loess Plateau. After measuring soil water and nitrate contents, the combined effects of climatic factors (precipitation, temperature, and potential evapotranspiration) and soil properties (soil texture, magnetic susceptibility, pH, EC, and soil organic carbon) were explored by wavelet analysis. Land use is the key factor regulating deep soil water and nitrate reservoirs, with high water deficit and low nitrate accumulation within 0–10 m under non-fertilized forestlands and shrublands. The positive and negative standardized ratios respectively suggested the synergistic and antagonistic relationships of water and nitrate under shallow- and deep-rooted vegetation. As the important agent for nitrate leaching, soil water is influenced by magnetic susceptibility and sand. Furthermore, soil water, pH, EC, and soil organic carbon are individually or simultaneously responsible for nitrate transport and transformation, especially at large scales (> 7.5 m). This study provides novel insights for vegetation and environmental management, and benefits the parameterizing of process-based hydrological and biogeochemical models at regional or global scales, especially in the deep unsaturated zones.

Screening, evaluation, and selection of yeasts with high ammonia production ability under nitrogen free condition from the cherry tomato (Lycopersicon esculentum var. cerasiforme) rhizosphere as a potential bio-fertilizer

Nitrogen (N) is an essential element for plant development and metabolism. It can be synthesized as nitrogenous substances that plants need, such as amino acids and nucleic acids. However, the N sources that plants can use directly are nitrate and ammonium, which either come from chemical fertilizers or are produced by microorganisms. However, too much chemical fertilizer causes nitrate accumulation in the soil of crops and leads to soil salinity. Applying bio-fertilizers to overcome land degradation caused by chemical fertilizers has been a public concern over the last few decades. Here, we collected the wild cherry tomato to isolate yeasts from its rhizosphere and evaluate their ability to promote plant growth. A total of 118 yeast strains were isolated from the rhizosphere and evaluated for their growth ability on nitrogen (N)-free media, ammonia production, and plant growth-promoting abilities. We reported that 66 yeasts showed growth ability on the N-free plate and all could produce ammonia (from 0.31 to 474.75 μg/mL) and indole-3-acetic acid (from 17.65 to 789.41 μM) with tryptophan as the precursor. Plant growth promotion was observed in Arabidopsis and baby pak choy plants following treatment with the yeast-producing N source as compared to control. We also found that only specific yeast strains could promote plant growth and development. It is suggested that plants may require suitable levels of yeast-producing ammonium. These results highlight the potential use of yeasts as bio-fertilizers under controlled and field conditions.

The apple GARP family gene MdHHO3 regulates the nitrate response and leaf senescence.

The regulation of plant gene expression by nitrate is a complex regulatory process. Here, we identified 90 GARP family genes in apples by genome-wide analysis. As a member of the GARP gene family, the expression of MdHHO3 (Malus domestica HYPERSENSITIVITY TO LOW PHOSPHATE-ELICITED PRIMARY ROOT SHORTENING1 HOMOLOG 3) is upregulated under N (nitrogen) supply. The results of DNA-binding site analysis and electrophoretic mobility shift assays (EMSA) showed that MdHHO3 binds to the motif-containing GAATC. Furthermore, MdHHO3 binds to its promoter sequence and inhibits its activity. In addition, the overexpression of MdHHO3 in apple calli resulted in less accumulation of nitrate in 35S:MdHHO3-GFP calli and downregulated the expression of the nitrate transport-related genes but upregulated the expression of the nitrate assimilation-related genes. Similarly, the expression of the nitrate transport-related genes was downregulated and the expression of the nitrate assimilation-related genes was upregulated in MdHHO3 overexpression Arabidopsis and tobacco plants. Interaction experiments showed that MdHHO3 could bind to the promoter MdNRT2.1 (NITRATE TRANSPORTER 2.1) and negatively regulate its expression. Moreover, the exposure of MdHHO3-overexpressing Arabidopsis and tobacco to nitrate deficiency resulted in an early senescence phenotype as compared to the WT plants. These results show that MdHHO3 can not only negatively regulate nitrate accumulation in response to nitrate but also promote early leaf senescence under nitrate deficiency. This information may be useful to further reveal the mechanism of the nitrate response and demonstrates that nitrate deficiency induces leaf senescence in apples.

Effects of spent mushroom substrate and nitrification inhibitor on nitrate accumulation in pepper: soil abiotic properties and endophytic and soil bacteria

Effects of spent mushroom substrate and nitrification inhibitor on nitrate accumulation in pepper: soil abiotic properties and endophytic and soil bacteria

Streptomyces strains can improve the quality properties and antifungal bioactivities of tomato fruits by impacting WRKY70 transcription factor gene and nitrate accumulation

The current study evaluated the effect of plant growth-promoting (PGP) strains of Streptomyces on yield, quality, and nitrate content of fruits, plant-microbe responses, and antifungal effect against blight disease caused by fungus pathogen Alternaria solani on tomato fruits in commercial greenhouse conditions. Greenhouse trials were done with four treatments including strains Y28, IC10, IT25, and commercial bio-fertilizer (Barvar NPK®) on tomato plants. In PGP treatments, the number of infected fruits significantly reduced (60%) compared to Barvar and control. Strain Y28 improved the quality of tomatoes more than other treatments. All three PGP treatments contained a higher level of total sugar concentration and antioxidant enzyme activities than Barvar and control. In contrast, PGP strains, especially Y28, significantly reduced nitrate accumulation (25%) compared to Barvar and control tomatoes. Streptomyces treatments induced more than a 20-fold increase in UDP and WRKY70 transcription factor gene expression relative to the control (P < 0.01). Based on the results, microbe-dependent plant defense induced by these strains is positively correlated to WRKY70 expression and nitrate reduction in commercial greenhouse conditions. These findings suggest that the commercial application of specific strains not only can illustrate an eco-friendly solution to induce resistance against fungal pathogens but also improve the quality properties of food plants with lower nitrate content.

Conversion from farmland to orchards has minor effects on nitrogen biological processes in deep loess deposits

High nitrate (NO3--N) accumulation has been observed globally in vadose zones due to the overuse of synthetic fertilizer, but its impacts on nitrogen (N) biological processes remain poorly understood, especially after land use conversion from farmlands to deep-rooted apple orchards. In this study, we collected paired soil samples to determine available N contents, NO3--N isotopes, and abundances of N functional genes (NFGs) in 10-m loess profiles under cultivated farmlands and adjacent apple orchards (n = 300). The average NO3--N accumulation under orchards was 4773 kg N ha−1 (10 times higher than farmlands), with the NO3--N profiles resembling a parabolic curve within 0 – 4 m below the surface. Regardless of excessive fertilizer application and well-developed root systems, the deep-rooted orchards had minor effects on N sources and biological processes in deep loess deposits, as indicated by our estimates of isotopes and NFGs abundances. We hypothesized that the limited and inactive microorganisms in the subsoil are more resistant to environmental disturbances, and that carbon source and ammonium substrate dominated the gene expression and occurrence of NFGs-indicated biological processes. The limited root biomass per unit depth and the inhibition effects of a dry soil horizon on root turnover and exudate release likely contributed to the less perturbed N biological processes under orchards. As the first study to explore N transformation processes in 10-m loess deposits, this study provided insights for complicated N biogeochemical cycles in arid regions with deep unsaturated soils and intensive agricultural land use.

Vacuolar nitrate efflux requires multiple functional redundant nitrate transporter in Arabidopsis thaliana.

Nitrate in plants is preferentially stored in vacuoles; however, how vacuolar nitrate is reallocated and to which biological process(es) it might contribute remain largely elusive. In this study, we functionally characterized three nitrate transporters NPF5.10, NPF5.14, and NPF8.5 that are tonoplast-localized. Ectopic expression in Xenopus laevis oocytes revealed that they mediate low-affinity nitrate transport. Histochemical analysis showed that these transporters were expressed preferentially in pericycle and xylem parenchyma cells. NPF5.10, NPF5.14, and NPF8.5 overexpression significantly decreased vacuolar nitrate contents and nitrate accumulation in Arabidopsis shoots. Further analysis showed that the sextuple mutant (npf5.10 npf5.14 npf8.5 npf5.11 npf5.12 npf5.16) had a higher 15NO3-uptake rate than the wild-type Col-0, but no significant difference was observed for nitrate accumulation between them. The septuple mutant (npf5.11 npf5.12 npf5.16 npf5.10 npf5.14 npf8.5 clca) generated by using CRISPR/Cas9 showed essentially decreased nitrate reallocation compared to wild type when exposed to nitrate starvation, though no further decrease was observed when compared to clca. Notably, NPF5.10, NPF5.14, and NPF8.5 as well as NPF5.11, NPF5.12, and NPF5.16 were consistently induced by mannitol, and more nitrate was detected in the sextuple mutant than in the wild type after mannitol treatment. These observations suggest that vacuolar nitrate efflux is regulated by several functional redundant nitrate transporters, and the reallocation might contribute to osmotic stress response other than mineral nutrition.

Growth and Mineral Relations of Beta vulgaris var. cicla and Beta vulgaris ssp. maritima Cultivated Hydroponically with Diluted Seawater and Low Nitrogen Level in the Nutrient Solution

There is an increasing interest in the use of seawater in horticulture. The objective of this study was to evaluate Beta vulgaris var. cicla (Swiss chard) and its wild ancestor B. vulgaris spp. maritima (sea beet) as potential crop species for seawater hydroponics or aquaponics. Both species were grown in a floating system for leaf production with recurrent harvests. The nutrient solutions contained different concentrations of nitrate (1 and 10 mM) and a synthetic sea salt (0 and 10 g L−1), in a factorial design, where the saline solution with a low nitrate level intended to mimic the typical nutritional conditions of saltwater aquaponics. In both species, increasing the salinity or reducing the N level in the nutrient solution reduced the crop yield and total dry biomass. In both Swiss chard and sea beet, the use of saline water resulted in a lower leaf concentration of K, Ca, Cu, and Mn, and a greater content of Na and Cl. In Swiss chard, an increase in Na and Cl and a decrease in K leaf content were found in successive harvests. On average, sea beet showed a higher leaf production and accumulation of nitrate than Swiss chard.

Rhodium Sulfides (Rh x S y ) as a Halide-Resistant Nitrate Reduction Electrocatalyst for Wastewater Remediation

Excess nitrate (NO3 –) accumulation in the environment due to human activities has adverse environmental and health effects and requires intervention. Electrocatalytic nitrate reduction (NO3RR), where nitrate is reduced in aqueous solution on electrode surfaces, is a promising method for sustainable remediation of nitrate to value-added chemicals such as NH3 [1]. A challenge for NO3RR is that nitrate adsorbs weakly to many catalyst surfaces and must compete with hydrogen and reaction intermediates for active sites [2, 3]. Metal catalysts which adsorb nitrate strongly at low overpotentials and are active for NO3RR, such as Rh, can be expensive. Better understanding the relationship between nitrate and hydrogen adsorption energies and nitrate reduction activity for known catalysts would allow faster identification of new, less expensive, active catalysts. Additionally, competition of nitrate for active sites is exacerbated in real waste streams, where other anions such as chloride are often present (e.g., introduced via resin recovery in ion-exchange membranes) and can compete for active sites, lowering the NO3RR activity. Determining chloride adsorption energies for nitrate reduction catalysts affected by the presence of chloride would provide useful information for understanding which materials would be affected by chloride and act as a guide for selecting chloride-resistant NO3RR catalysts.We report the competitive adsorption of nitrate and hydrogen and the reaction mechanism of NO3RR. By using adsorption energies of nitrate and hydrogen as descriptors, we qualitatively understand many of the observed trends in NO3RR activity on metal surfaces through a Langmuir-Hinshelwood reaction mechanism [3]. We show the voltage dependence of NO3RR on platinum group metals, where competitive adsorption of hydrogen and nitrate or nitrate intermediates causes a maximum in NO3RR activity with potential. Identifying these activity descriptors allows rapid computational screening to identify new promising catalysts. Using cyclic voltammetry on Pt and Rh, we observe that the chloride adsorption voltage window overlaps with the maximum activity for NO3RR, due to the related adsorption energies of nitrate and chloride [4]. Using steady state current densities, we show that Rh is more active than Pt for NO3RR in acidic conditions but the addition of even 1 mM chloride lowers NO3RR activity by 30-60%, with Rh more affected by chloride than Pt. The lowering of activity is attributed to competitive adsorption between chloride and nitrate for active sites. Using DFT, we compute the chloride and nitrate adsorption energies on a series of metals and observe linear scaling relations, such that it is unlikely any transition metal binds chloride weakly while adsorbing nitrate strongly. To address chloride poisoning, we examine rhodium sulfide (Rh x S y ), which is an electrocatalyst with notable halide resistance. We show that Rh x S y is more active for NO3RR in acidic media with and without chloride than Pt or Rh and discuss plausible active sites.

Effect of growth seasons and nitrogen fertilization on the growth, yield and nitrate accumulation of lettuce (Lactuca sativa L.) plants

In modern agriculture, the nitrate accumulation in vegetables has become a serious threat to human health. That caused by an imbalance between nitrate absorption and assimilation in plants. Nitrogen fertilization and light intensity are the main factors affected nitrate accumulation. Therefore, a pot experiment was conducted during two successive summer and winter seasons of 2019/20 at the greenhouse of Fac. Agric., Cairo Univ., Giza, Egypt, on lettuce (Lactuca sativa L. var. longifolia Lam) plants to investigate the effect of growth seasons (summer and winter), different rates (0, 60, 90 and 120 Kg N fed-1) and sources (CO (NH2)2, NH4NO3 and (NH4)2SO4) of nitrogen fertilizers on lettuce growth and nitrate concentrations. The results showed that fresh and dry weight, yield and nutrient contents of lettuce plants increased gradually according to increasing dose of nitrogen, up to 90 Kg N fed-1 and the magnitude of increase, according to different N fertilizers used , was in the following order: CO (NH2)2 &gt; NH4NO3 &gt; (NH4)2SO4. The accumulation of nitrate was higher in winter compared to summer season for both inner and outer leaves.

The Effect of Flushing on the Nitrate Content and Postharvest Quality of Lettuce (Lactuca sativa L. Var. Acephala) and Rocket (Eruca sativa Mill.) Grown in a Vertical Farm

Hydroponics is the most widely used technique in closed cultivation environments, and this system is often used for the cultivation of baby leaf vegetables. These species can accumulate high levels of nitrates; for this reason, the control of growing conditions is a crucial factor for limiting their content, especially in protected cultivations. The aim of this work was to reduce nitrate accumulation in leafy vegetables grown in a vertical farm while preserving the quality at harvest as well as during storage. This objective was achieved by completely replacing the nutrient solution with water a few hours before harvest (“flushing”). The trials were carried out on lettuce (Lactuca sativa L. Var. Acephala, cv. Greenet) and rocket (Eruca sativa Mill., cv. Rome). Three independent trials were conducted on lettuce, applying the flushing treatment 24 h and 48 h prior to harvest. One trial was conducted on rocket, applying the treatment 48 h before harvesting. Sampling and related analyses were carried out at harvest and during the storage period to determine chlorophyll, leaf fluorescence, total sugars, chlorophyll (a + b), carotenoids, phenolic index, anthocyanins and nitrate content. Moreover, relative humidity (RH%), O2% and CO2% determination inside the package headspace were monitored during storage. The results obtained indicate that it is possible to reduce the nitrate concentration by up to 56% in lettuce and 61% in rocket while maintaining the product quality of baby leaves by replacing the nutrient solution with tap water before harvest.