Comprehensive understanding of the thriving electrocatalytic nitrate/nitrite reduction to ammonia under ambient conditions

Ammonia(NH_(3))is a multifunctional compound that is an important feedstock for the agricultural and pharmaceutical industries and attractive energy storage medium.At present,NH_(3)synthesis is highly dependent on the conventional Haber–Bosch process that operates under harsh conditions,which consumes large quantities of fossil fuels and releases a large amount of carbon dioxide.As an alternative,electrosynthesis is a prospective method for producing NH_(3)under normal temperature and pressure conditions.Although electrocatalytic nitrogen reduction to ammonia has attracted considerable attentions,the low solubility of N_(2)and high N≡N cracking energy render the achievements of high NH_(3) yield rate and Faradaic efficiency difficult.Nitrate and nitrite(NO_(x)^(-))are common N-containing pollutants.Due to their high solubilities and low dissociation energy of N=O,NO_(x)^(-)−are ideal raw materials for NH_(3) production.Therefore,electrocatalytic NO_(x)^(-)−reduction to NH_(3)(eNO_(x)RR)is a prospective strategy to simultaneously realise environmental protection and NH_(3) synthesis.This review offers a comprehensive understanding of the thriving eNO_(x)RR under ambient conditions.At first,the popular theory and mechanism of eNO_(x)RR and a summary of the measurement system and evaluation criteria are introduced.Thereafter,various strategies for developing NO_(x)−reduction catalysts are systematically presented and discussed.Finally,the challenges and possible prospects of electrocatalytic NO_(x)^(-1) reduction are outlined to facilitate energy-saving and environmentally friendly large-scale synthesis of NH_(3) in the future.

Assessment of Nitrates and Nitrites in Borehole Water from the Southern and the Northern Region of Côte d’Ivoire (West Africa)

This study aimed to evaluate the quality of water from village boreholes by measuring physicochemical parameters such as nitrates, nitrites, and total organic carbon (TOC). Forty-five (45) village pumps from the Southern (Basse Côte) and the Northern (Korhogo) region of Cte d’Ivoire (west Africa) were sampled. Physicochemical parameters such as temperature, pH, conductivity at 25˚C, and turbidity were determined in situ, while nitrite and nitrate were analyzed according to ISO 10304-1 (2007) standard and total organic carbon (TOC) by NF EN 1484 (1997) standard. The results showed that the borehole waters of the Basse Côte and Korhogo analyzed are acidic, with an average temperature of 27.51˚C ± 0.16˚C and 29.95˚C ± 0.51˚C respectively for the Basse Côte and Korhogo regions. The borehole waters of the Basse Côtedo not contain nitrites, while those of Korhogo have average nitrite contents of 0.32 mg/l. The average nitrate rate in the waters of the Basse Côte and Korhogo are 12.08 ± 2.11 mg/l and 11.03 ± 3.18 mg/l respectively. The average TOC concentration of the waters of the Basse Côte is 1.28 ± 0.32 mg/l and that of Korhogo is 0.56 ± 0.09 mg/L. The study showed that the borehole waters of the Basse Côte and Korhogo have average temperatures between 27.4˚C and 29.95˚C with a slightly acidic pH value and acceptable salinity. The TOC concentrations obtained at the different sampling points were all below the French standard (2 mg/L) except for certains pumps of the Basse Côte. The water samples from the Basse Côte were devoid of nitrite. On the other hand, those from Korhogo revealed the presence of nitrite. Also, the borehole waters of the regions of the Basse Côte and Korhogo contain relatively high nitrate contents, presumably due to anthropometric activity. Overall, our study on the quality of drinking water showed that the waters analyzed are in compliance with international standards and safe for consumption.

Nitrate-nitrite-nitrosamines exposure and the risk of type 1 diabetes: A review of current data

The potential toxic effects of nitrate-nitrite-nitrosamine on pancreatic β cell have remained a controversial issue over the past two decades. In this study, we reviewed epidemiological studies investigated the associations between nitrate-nitrite-nitrosamines exposure, from both diet and drinking water to ascertain whether these compounds may contribute to development of type 1 diabetes. To identify relevant studies, a systematic search strategy of Pub Med, Scopus, and Science Direct was conducted using queries including the key words "nitrate", "nitrite", "nitrosamine" with "type 1 diabetes" or "insulin dependent diabetes mellitus". All searches were limited to studies published in English. Ecologic surveys, case-control and cohort studies have indicated conflicting results in relation to nitrate-nitrite exposure from drinking water and the risk of type 1 diabetes. A null, sometimes even negative association has been mainly reported in regions with a mean nitrate levels < 25 mg/L in drinking water, while increased risk of type 1 diabetes was observed in those with a maximum nitrate levels > 40-80 mg/L. Limited data are available regarding the potential diabetogenic effect of nitrite from drinking water, although there is evidence indicating dietary nitrite could be a risk factor for development of type 1 diabetes, an effect however that seems to be significant in a higher range of acceptable limit for nitrate/nitrite. Current data regarding dietary exposure of nitrosamine and development of type 1 diabetes is also inconsistent. Considering to an increasing trend of type 1 diabetes mellitus(T1DM) along with an elevated nitrate-nitrite exposure, additional research is critical to clarify potential harmful effects of nitrate-nitritenitrosamine exposure on β-cell autoimmunity and the risk of T1DM.

Determination of hydroxyl radicals with salicylic acid in aqueous nitrate and nitrite solutions

The qualitative and quantitative analyses of reactive oxygen species are essential to determine their steady-state concentration and related reaction mechanisms in environmental aquatic systems. In this study, salicylic acid was employed as an innovative molecular probe of hydroxyl radical(OH) generated in aqueous nitrate and nitrite solutions through photochemical reactions. Kinetic studies showed that the steady-state concentrations of OH in aqueous NO- 3(10 mmol/L, pH=5) and NO- 2(10 mmol/L, pH=5) solutions under ultraviolet irradiation were at a same magnitude, 10 -15 mol/L. Apparent quantum yields of OH at 313 nm were measured as 0.011 and 0.07 for NO- 3 and NO- 2 respectively, all comparable to the results of previous studies.

A simple derivative spectrophotometric method for simultaneously detecting nitrate and nitrite in plasma treated water

A spectrophotometric technique is developed to simultaneously quantify nitrate and nitrite in plasma treated water.The measurement is based on examining the inflection points(wavelengths)in the derivative absorbance of the nitrate or nitrite solution.At the inflection points of the pure nitrate solution,the derivative absorbance is zero and independent of the nitrate’s concentration,and thus the nitrite’s concentration in a mixed nitrate and nitrite solution can be obtained by using the Beer’s law at these points.The nitrate’s concentration can also be achieved from the inflection points of nitrite in the same manner.The relation between the tested substance’s(nitrate or nitrite)concentration and the second-or the third-order absorbances is obtained at these inflection points.Test measurements for mixed aqueous solutions of nitrate and nitrite with or without hydrogen peroxide confirm the reliability of this technique.We applied this technique to quantify the nitrate and nitrite generated in air plasma treated aqueous solutions.The results indicate that both nitrate and nitrite concentrations increase with the plasma treatment time,and the nitrite species is found to be generated prior to the nitrate species in the air plasma treated aqueous solution.Moreover,the production rate of total nitrogen species is independent of the solutions’p H value.These results are relevant to diverse applications of plasma activated solutions in materials processing,biotechnology,medicine and other fields.

Determination of Nitrate and Nitrite Contents of Syrian White Cheese

The levels of nitrate and nitrite were determined in 102 samples of Syrian white cheese which represents the major production of total cheeses, manufactured mainly from cow’s milk and sheep’s milk in a less degree. Determination of nitrate and nitrite levels has been made by spectrophotometric method. The results for nitrate in cow’s and sheep’s milk cheeses reveal an average of 5.10 and 6.25 mg/kg, respectively. The results for nitrite in cow’s and sheep’s milk cheese were found to contain 1.24 and 1.31 mg/kg as an average, respectively. Several factors can play a role in the interpretation of the high nitrate content, such as livestock nutrition by forge with high nitrate load and water contaminated with nitrogen fertilizer and domestic effluents, primitive production techniques in many cases, and adding nitrate salts to prevent the growth of gas-producing bacteria caused by failing in the hygienic conditions. There is a necessity to apply strict controls to reduce the presence of these two anions in the Syrian white cheese.

Seasonal Cycle Analysis of the Nitrate Nitrogen and Nitrite Nitrogen in the Bohai Sea

During 1985-1987, the concentration of nitrate nitrogen was higher in the Laizhou Bay and the Bohai Bay while that of nitrite nitrogen was higher in the Liaodong Bay and the Bohai Bay. The concentration of nitrate nitrogen was highest in winter and lowest in summer while that of nitrite nitrogen was highest in autumn and lowest in spring. The seasonal variation of the concentration of nitrate nitrogen was maximum in the Laizhou Bay and the Bohai Bay while that of the concentration of nitrite nitrogen was maximum in the Liaodong Bay. There was a great difference in the concentration of nitrate nitrogen between the surface and the bottom in autumn and in the concentration of nitrite nitrogen between the surface and the bottom in summer. The main reason for the seasonal variations of the concentration of nitrate nitrogen and nitrite nitrogen was the marine biochemical process. The nitrate nitrogen and nitrite nitrogen in the Bohai Sea basically maintained a quasi-equilibrium state seasonal cycle. The quasi-equilibrium state seasonal cycle of nitrate nitrogen and nitrite nitrogen at the bottom was stable while that at the surface was liable to variations caused by other factors.

Impact of petroleum refining activities on nitrate and nitrite content of edible vegetables and on their <i>in vivo</i>kinetics in albino rats

The influence of pollution from petroleum refining activities on the levels of nitrates and nitrites in five edible vegetable species was investigated. Besides, the kinetics of nitrite and nitrate was studied in vivo using albino rats with focus on the possible influence of concentration difference on kinetics and implications to toxicity. Leaf samples of the five vegetable species were collected randomly from various locations within Eleme, a host community of Port Harcourt Refinery Company and the Indorama Petrochemical Company. Also, samples were collected from Umuahia, which served as pollution-free control. The leaf samples were analyzed for their nitrite and nitrate contents. Nitrite was determined spectrophotometrically while nitrate was determined after cadmium column reduction. Results showed that samples from Eleme had higher mean nitrate (349.20 mg/100g dry leaf mass;P 0.05) as compared to the same samples from Umuahia. Solutions of nitrate and nitrite, equivalent in concentration to mean nitrate and nitrite content of the vegetable samples from the two locations were administered enterally to four groups of albino rats. Analysis of their blood levels were monitored five times at 30 minutes intervals following administration. Rates of change of blood nitrites and nitrates were found to be fairly constant in absorption as well as in the elimination phase. Their peak blood concentrations varied proportionately with their concentrations in administered solutions. However, peak blood nitrate was attained later in group of animals receiving higher amount of nitrate solution. Refining activities may pre-dispose people living within Eleme community to health hazards through contamination of edible vegetables.

Homemade versus Commercial Jarred Baby Foods with Regard to Nitrites and Nitrates Content

This paper presents results of nitrites and nitrates determination in two types of baby foods： commercial products in jars and their homemade conventional counterparts. Nitrites levels in all analyzed samples were below of the detection limit （〈 0.9 mg/kg） of applied spectrophotometric method with Griess reagent. Nitrates contents in commercial products ranged： 9.1-38.1 mg/kg while in homemade baby foods levels between 26.6 mg/kg and 118.8 mg/kg were obtained. All the contents of nitrates were lower than the EU legislation maximum limit （200 mg/kg）. Comparison of each type of commercial product with its homemade counterpart baby food evidenced significant differences （p 〈 0.05） in average nitrates levels in favor of the first type. Apart from determining and comparing the levels of nitrates in the baby food samples also risk assessment for an average 6-months old infant to nitrates exposure was conducted. The estimated nitrates intake with a typical portion of 200g of baby food ranged between 6% and 25.7% of acceptable daily intake for commercial and from 18.0% to 80.3% for homemade ones.

Zoning of Nitrite and Nitrate Concentration in Groundwater Using Geografic Information System (GIS), Case Study: Drinking Water Wells in Yazd City

Studies have demonstrated that the presence of nitrate and nitrite in drinking water can cause some disease such as cancer and blu baby in the infant. The Environmental Protection Agency (EPA) has since adopted the 10 mg/L standard as the maximum contaminant level (MCL) for nitrate-nitrogen and 1 mg/L for nitrite-nitrogen for regulated public water systems. Given the importance of nitrate and nitrite in drinking water as well as GIS ability in spatial analysis of various factors in the groundwater, this study aimed to evaluate concentration of nitrate and nitrite in the drinking water wells of Yazd using two IDW (Inverse Distance Weighting) and Kriging models. In this descriptive study, the applied data on the water quality of underground water of Yazd Environmental Health Office and the average annual nitrate and nitrite in 2015 were related to 24 wells in the studied area. The nitrate and nitrite rate in groundwater in wells was compared to the standard amount of Institute of Standard and Industrial Researches and then was analyzed via Arc GIS software using IDW and Kriging interpolation methods. The mean concentration of nitrate was 17.62 ± 3.08 mg/l and for nitrite was 0.011 ± 0.003 mg/l in the wells. In the all studied zone, the nitrate and nitrite rate was in the standard range according to the National Standard of Iran (No. 1053). In this study, Kriging interpolation method was more efficient than IDW method.

Optimization of an Alternative Methodology for Simultaneous Analysis of Nitrite and Nitrate in Water from Urban Stream by Capillary Electrophoresis under Direct UV Detection

An alternative methodology for simultaneous determination of nitrite and nitrate by capillary zone electrophoresis using direct detection UV at 210 nm under reverse electrosmotic flow is proposed. The choice of the electrolyte composition has taken account: the mobility of the anion buffer and of the solutes;the low absorbance of the buffer in 210 nm;high base line stability and analysis time. The electrolyte optimized has consisted of 100 mmol.L–1 TRIS/HCl buffer and 0.15 mmol.L–1 CTAB at pH 8.2. The proposed method was applied successfully in the analysis of nitrite and nitrate in samples from urban stream in the absence of usual sample pretreatment.

NO Adsorption on Ag/Pt（110）-（1×2） Bimetallic Surfaces： Unexpected Formation of Nitrite/nitrate Surface Species

NO adsorption on Ag/Pt（110）-（1×2） bimetallic surfaces at room temperature was investigated by means of Auger electron spectroscopy, X-ray photoelectron spectroscopy and thermal desorption spectroscopy. An unexpected formation of nitrite/nitrate surface species on Ag/Pt（110）-（1 ×2） bimetallic surfaces is observed, then decompose at elevated temperatures to form N2. However, such nitrite/nitrate surface species do not form on clean Pt（110） and Ag-Pt alloy surfaces upon NO exposure at room temperature. The formation of nitrite/nitrate surface species on Ag/Pt（110）-（1×2） bimetallic surfaces is attributed to high reactivity of highly coordination-unsaturated Ag clusters and the synergetic effect between Ag clusters and Pt substrate.

Optimize Operation of Partial Denitrification System for Simultaneous Treatment of Low C/N Municipal and Nitrate Wastewaters

In order to realize the simultaneous treatment of low C/N municipal and nitrate( NO3^--N) wastewaters,a sequencing batch reactor( SBR) was used to optimize the partial denitrification( PD),which the influent substrate and the anoxic reaction time were appropriately controlled. The carbon and nitrogen removal and the characteristic parameters of PD during long-term operation were studied. Experimental results showed that the PD showed stable characteristics of nitrogen and carbon removal and NO2^--N accumulation after an adaptation of 20 d with municipal wastewater used. The anoxic reaction time was extended from 50 to 70 min with the initial COD/NO3^--N decreased from 3. 0 to about 2. 5. When the influent NO3^--N was 117. 93 mg/L,the effluent NO2^--N and NAR were 23. 10 mg/L and 82. 26%,respectively,and the nitrogen and carbon removal rate reached 91. 76% and 65. 70%,respectively. The effluent NO2^--N/NH4^+ -N meantime reached 1.17-1. 22. Moreover,the cumulative concentration of NO2^--N and the system NAR increased linearly with the consumption of NO3^--N and COD,and the change trend was highly significant within 0-20 min,and gradually flattened.

The Spatial Distribution of Nitrite Concentrations in a Large Drinking Water Distribution System in Finland

Nitrite in drinking water is a potential health hazard and monitoring its concentrations in distributed water is of paramount importance. When monochloramine is used in secondary disinfection in drinking water distribution systems (DWDSs), nitrite is often formed by nitrification in the biofilm on the inner surface of distribution pipes. This article attempts to identify areas with a risk of increased nitrite concentrations as well as the main reasons leading to nitrite occurrence in a large urban DWDS in Finland using spatial inspection of obligatory monitoring data. Nitrification was found to occur throughout the study area, though nitrite was not increased everywhere. Instead, nitrite was increased close to the water treatment plants (WTPs) and was connected to fresh drinking water than stagnant drinking water. Temperature effects on nitrite concentrations were surprisingly insignificant, even though it is well known that nitrification reactions are affected by temperature. The temperature dependence of ammonium and total residual chlorine was more significant than the dependence of nitrite. The findings of this study emphasize the need to monitor nitrite concentrations close to WTPs.

A review of salivary composition changes induced by fasting and its impact on health

Human saliva is an indispensable fluid that maintains a healthy oral cavity which otherwise can lead to oral diseases(dental caries and periodontitis).In addition,salivary metabolites and microbiome profile provide early detection of systemic diseases such as cancer and obesity.Salivary diagnostic has gained popularity due to its non-invasive sampling technique.Fasting(abstinence from food or drink or both)research for weight loss and improve health is common,but studies using fasting saliva are scarce.Some metabolites in fasting saliva have been reported with interesting results,which can be enhanced by considering different confounding factors.For example,fasting saliva contains higher salivary nitrite,which is related to nitric oxide(NO).NO is a vasodilator supporting the healthy function of endothelial cells and its deficiency is connected to many diseases.The timely supply of NO through exogenous and endogenous means is highlighted and the potential advantage of fasting salivary composition changes in relation to COVID-19 infection is speculated.This review aims to provide a general discussion on the salivary composition,properties,and functions of the whole saliva,including the health benefits of fasting.

Effect of carbon source on the denitrification in constructed wetlands

The ability of constructed wetlands with different plants in nitrate removal were investigated. The factors promoting the rates of denitrification including organic carbon, nitrate load, plants in wetlands, pH and water temperature in field were systematically investigated. The results showed that the additional carbon source （glucose） can remarkably improve the nitrate removal ability of the constructed wetland. It demonstrated that the nitrate removal rate can increase from 20% to more than 50% in summer and from 10% to 30% in winter, when the nitrate concentration was 30-40 rag/L, the retention time was 24 h and 25 mg/L dissolved organic carbon （DOC） was ploughed into the constructed wetland. However, the nitrite in the constructed wetland accumulated a little with the supply of the additional carbon source in summer and winter, and it increased from 0.15 to 2 mg/L in the effluent. It was also found that the abilities of plant in adjusting pH and temperature can result in an increase of denitrification in wetlands. The seasonal change may also impact the denitrification.

Rapid testing methods for food contaminants and toxicants

Food safety is one of the major concerns in every country regardless of the economic and social development. The frequent occurrence of food scandals in the world has led the Chinese government to implement several strategies to fortify the food supply system to a high food safety standard. This relies heavily on laboratory testing services but conventional methods for detection of food contaminants and toxicants are limited by sophisticated sample preparation procedures, long analysis time, large instruments and professional personnel to meet the increasing demands. In this review, we have incorporated most of the current and potential rapid detection methods for many notorious food contaminants and toxicants including microbial agents, toxic ions, pesticides, veterinary drugs and preservatives, as well as detection of genetically modified food genes and adulterated edible oil. Development of rapid, accurate, easy-to-use and affordable testing methods could urge food handlers and the public to actively screen for food contaminants and toxicants instead of passively relying on monitoring by the government examination facility. This review also provides several recommendations including how to encourage the public to engage in the food safety management system and provide optimal education and financial assistance that may improve the current Chinese food safety control system.

Serum levels of soluble Fas, nitric oxide and cytokines in acute decompensated cirrhotic patients

AIM： To evaluate plasma levels of nitrite/nitrate （NOx）, soluble Pas （spas） antigen, tumor necrosis factor alpha （TNF-α） and interleukin-6 （IL-6） in patients with compensated and acute decompensated cirrhosis and to evaluate mediators causing acute decompensation in liver cirrhosis, METHODS： This prospective study was conducted in the medical intensive care unit of an academic tertiary center, Fifty-five patients with acute decompensation （gastrointestinal hemorrhage, encephalopathy, hydropic decompensation） and twenty-five patients with compensated liver drrhosis were included, Blood samples were taken for analyses of spas, Nox, IL-6, TNF-α, Liver enzymes and kidney functions were also tested, RESULTS： In patients with acute decompensation, plasma spas levels were higher than in non-decompensated patients （15305 ± 4646 vs 12458± 4322 pg/mL, P 〈 0.05）. This was also true for the subgroup of patients with alcoholic liver cirrhosis （P 〈 0.05）. The other mediators were not different and none of the parameters predicted survival, except for ALT （alanine-aminotransferase）. In patients with portal-hypertension-induced acute hemorrhage, NOx levels were significantly lower than in patients with other forms of decompensation （70.8 ± 48.3 vs 112.9 ± 74.9 pg/mL, P 〈 0.05）. When NOx levels were normalized to creatinine levels, the difference disappeared. IL-6, TNF-α and spas were not different between bleeders and non-bleeders. In decompensated patients spas, IL-6 and NOx levels correlated positively with creatinine levels, while IL-6 levels were dependent on Child class. CONCLUSION： In acute decompensated cirrhotic patients sPas is increased, suggesting a role of apoptosis in this process and patients with acute bleeding have lower NOx levels, However, in this acute complex clinical situation, kidney function seems to have a predominant influence on mediator levels,

Adrenomedullin in cirrhotic and non-cirrhotic portal hypertension

AIM:Adrenomedullin (ADM) is a potent vasodilator peptide. ADM and nitric oxide (NO) are produced in vascular endothelial cells.Increased ADM level has been linked to hyperdynamic circulation and arterial vasodilatation in cirrhotic portal hypertension (CPH).The role of ADM in non-cirrhotic portal hypertension (NCPH) is unknown,plasma ADM levels were studied in patients with NCPH,compensated and decompensated cirrhosis in order to determine its contribution to portal hypertension (PH) in these groups. METHODS:There were 4 groups of subjects.Group 1 consisted of 27 patients (F/M:12/15) with NCPH due to portal and/or splenic vein thrombosis (mean age:41±12 years),group 2 consisted of 14 patients (F/M:6/8) with compensated (Child-Pugh A) cirrhosis (mean age:46±4), group 3 consisted of 16 patients (F/M:6/10) with decompensated (Child-Pugh C) cirrhosis (mean age:47±12). Fourteen healthy subjects (F/M:6/8) (mean age:44±8) were used as controls in Group 4.ADM level was measured by ELISA.NO was determined as nitrite/nitrate level by chemoluminescence. RESULTS:ADM level in Group 1 (236±61.4 pg/mL) was significantly higher than that in group 2 (108.4±28.3 pg/mL) and group 4 (84.1±31.5 pg/mL) (both P<0.0001) but was lower than that in Group3 (324±93.7 pg/mL) (P=0.002).NO level in group 1 (27±1.4 μmol/L) was significantly higher than that in group 2 (19.8±2.8 μmol/L) and group 4 (16.9±1.6 μmol/L) but was lower than that in Group 3 (39±3.6 μmol/L) (for all three P<0.0001).A strong correlation was observed between ADM and NO levels (r=0.827,P<0.0001). CONCLUSION:Adrenomedullin and NO levels were high in both non-cirrhotic and cirrhotic portal hypertension and were closely correlated,Adrenomedullin and NO levels increased proportionally with the severity of cirrhosis,and were significantly higher than those in patients with NCPH. Portal hypertension plays an important role in the increase of ADM and NO.Parenchymal damage in cirrhosis may contribute to the increase in these parameters.

DYNAMIC CHANGES OF INORGANIC NITROGEN AND ASTAXANTHIN ACCUMULATION IN HAEMATOCOCCUS PLUVIALIS

This study on dynamic changes of culture color, astaxanthin and chlorophylls, inorganic N including N NO - 3, N NO - 2 and N NH + 4 in batch culture of Haematococcus pluvialis exposed to different additive nitrate concentration showed (1) ast/chl ratio was over 0.8 for brown and red algae, but was usually less than 0.5 for green and yellow algae; (2) N NO - 3, in general, was unstable and decreased, except for a small unexpected increase in nitrate enriched treatment groups; (3) measurable amounts of N NO - 2 and N NH + 4 were observed respectively with three change modes although no external nitrite and ammonia were added into the culture; (4) a non linear correlation between ast/chl ratio (or color) changes and the levels of N NO - 3 , N NO - 2 , N NH + 4 in H. pluvialis culture; (5) up and down variation of the ast/chl ratio occurred simultaneously with a perceptible color change from yellow to brown (or red) when N NO - 3, N NO - 2 and N NH + 4 fluctuated around 30, 5, 5 μmol/L respectively; (6) existence of three dynamic modes of N NO - 3, N NO - 2 and N NH + 4 changes, obviously associated with initial external nitrate; (7) the key level of total inorganic N concentration regulating the above physiological changes during indoor cultivation was about 50 μmol/L; and (8) 0.5-10 mmol/L of nitrate was theoretically conducive to cell growth in batch culture.