Root GS and NADH-GDH Play Important Roles in Enhancing the Ammonium Tolerance in Three Bedding Plants

Ammonium is a paradoxical nutrient because it is more metabolically efficient than nitrate, but also causes plant stresses in excess, i.e., ammonium toxicity. Current knowledge indicates that ammonium tolerance is species-specific and related to the ammonium assimilation enzyme activities. However, the mechanisms underlying the ammonium tolerance in bedding plants remain to be elucidated. The study described herein explores the primary traits contributing to the ammonium tolerance in three bedding plants. Three NH₄⁺:NO₃⁻ ratios (0:100, 50:50, 100:0) were supplied to salvia, petunia, and ageratum. We determined that they possessed distinct ammonium tolerances: salvia and petunia were, respectively, extremely sensitive and moderately sensitive to high NH₄⁺ concentrations, whereas ageratum was tolerant to NH₄⁺, as characterized by the responses of the shoot and root growth, photosynthetic capacity, and nitrogen (amino acid and soluble protein)-carbohydrate (starch) distributions. An analysis of the major nitrogen assimilation enzymes showed that the root GS (glutamine synthetase) and NADH-GDH (glutamate dehydrogenase) activities in ageratum exhibited a dose-response relationship (reinforced by 25.24% and 6.64%, respectively) as the NH₄⁺ level was raised from 50% to 100%; but both enzyme activities were significantly diminished in salvia. Besides, negligible changes of GS activities monitored in leaves revealed that only the root GS and NADH-GDH underpin the ammonium tolerances of the three bedding plants.     

Isopolyoxorhenates observed by positive ion electrospray mass spectrometry

Unknown positive ion isopolyoxorhenates have been observed using electrospray ionization mass spectrometry (ESI+). The ESI+ studies of ammonium and alkali metal (Na⁺ and K⁺) perrhenate salts in aqueous solution at pH 4.5 show the existence of the series [A_x+1Re^VII_xO_4x]⁺ (where x=1–5 and A=NH₄⁺, Na⁺ and K⁺). In the potassium perrhenate system, the series [K_x+2Re^VRe^VII_xO_4x+3]⁺ (x=0–4) has also been characterised. All of these four series have {AReO₄} as the aggregation unit. In the ammonium perrhenate system, the monomeric Re(VII)-containing species, [(NH₄)₂(H₂ReO₅)]⁺, [(NH₄)₃(HReO₅)]⁺ and [(NH₄)₄(ReO₅)]⁺ were also detected.     

Genome-Wide Identification and Expression Analysis of AMT and NRT Gene Family in Pecan (Carya illinoinensis) Seedlings Revealed a Preference for NH4+-N

Nitrogen (N) is a major limiting factor for plant growth and crop production. The use of N fertilizer in forestry production is increasing each year, but the loss is substantial. Mastering the regulatory mechanisms of N uptake and transport is a key way to improve plant nitrogen use efficiency (NUE). However, this has rarely been studied in pecans. In this study, 10 AMT and 69 NRT gene family members were identified and systematically analyzed from the whole pecan genome using a bioinformatics approach, and the expression patterns of AMT and NRT genes and the uptake characteristics of NH₄⁺ and NO₃⁻ in pecan were analyzed by aeroponic cultivation at varying NH₄⁺/NO₃⁻ ratios (0/0, 0/100,25/75, 50/50, 75/25,100/0 as CK, T1, T2, T3, T4, and T5). The results showed that gene duplication was the main reason for the amplification of the AMT and NRT gene families in pecan, both of which experienced purifying selection. Based on qRT-PCR results, CiAMTs were primarily expressed in roots, and CiNRTs were majorly expressed in leaves, which were consistent with the distribution of pecan NH₄⁺ and NO₃⁻ concentrations in the organs. The expression levels of CiAMTs and CiNRTs were mainly significantly upregulated under N deficiency and T4 treatment. Meanwhile, T4 treatment significantly increased the NH₄⁺, NO₃⁻, and NO₂⁻ concentrations as well as the Vmax and Km values of NH₄⁺ and NO₃⁻ in pecans, and Vmax/Km indicated that pecan seedlings preferred to absorb NH₄⁺. In summary, considering the single N source of T5, we suggested that the NH₄⁺/NO₃⁻ ratio of 75:25 was more beneficial to improve the NUE of pecan, thus increasing pecan yield, which provides a theoretical basis for promoting the scale development of pecan and provides a basis for further identification of the functions of AMT and NRT genes in the N uptake and transport process of pecan.     

Kinetics of ligand exchange reaction of Cu(II)-ammine complex with poly(vinyl alcohol) in aqueous solution

The kinetics of the ligand exchange reaction of the Cu(II)-ammine complex with poly(vinyl alcohol) (PVA) has been studied by a stopped-flow method at pH 9–10, at μ=0.1 (NH₄Cl) and at 25°C. The reaction is initiated by the formation of unstable [Cu(NH₃)₃]²⁺ by the attack of H⁺ on Cu(II)-ammine complex, and proceeds through the mixed complex {[Cu(NH₃)₃(O?PVA)]²⁺}. This step may be rate-determining, followed by a rapid reaction. Finally, the Cu(II) ion is taken up by PVA. The rate is given by d[Cu(II)?PVA]/dt=k[H⁺]{[Cu(NH₃)₄]²⁺}[PVA]/[NH₄Cl], where k=k₁ + k′₂[H⁺], k₁=4.25× 10s^?1 and k′₂=5.20× 10¹¹l mol^?1s^?1.     

Process rates of nitrogen cycle in uppermost topsoil after harvesting in no-tilled and ploughed agricultural clay soil

No-till is considered an agricultural practice beneficial for the environment as soil erosion is decreased compared to ploughed soils. For on overall evaluation of the benefits and disadvantages of this crop production method, understanding the soil nutrient cycle is also of importance. The study was designed to obtain information about gross soil nitrogen (N) process rates in boreal no-tilled and mouldboard ploughed spring barley (Hordeum vulgare L.) fields after autumn harvesting. In situ soil gross N transformation process rates were quantified for the 5 cm topsoil in 9 days’ incubation experiment using ¹⁵N pool dilution and tracing techniques and a numerical ¹⁵N tracing model. Gross N mineralization into ammonium (NH₄ ⁺) and NH₄ ⁺ immobilization were the most important N transformation processes in the soils. The gross mineralization rate was 14% and NH₄ ⁺ immobilization rate 64% higher in no-till than in ploughing. Regardless of the faster mineralization, the gross rate of NH₄ ⁺ oxidation into nitrate (NO₃ ^?) in no-till was one order of magnitude lower compared the ploughing. The results indicate that the no-tilled soils have the potential to decrease the risk for NO₃ ^? leaching due to slower NH₄ ⁺ oxidation.     

Simultaneous removal of low concentrations of ammonium and humic acid from simulated groundwater by vermiculite/palygorskite columns

Vermiculite and palygorskite are common clay minerals having large surface area and high cation exchange capacities. They have different affinities for ammonium (NH₄⁺) and humic acid (HA), and hence were combined to remove NH₄⁺ and HA simultaneously from simulated groundwater in column tests. Three columns were assembled by filling the columns with the same amount of vermiculite and palygorskite but in different arrangements. The simulated groundwater containing NH₄⁺ and HA was pumped to the columns in an upward direction. The concentrations of N-NH₄⁺ and HA at different height of the columns were measured over time. No significant differences on HA removal among the three column settings were observed. However, the NH₄⁺ removal efficiencies were significantly different among the three column settings. For the column filled with separate vermiculite and palygorskite layers, NH₄⁺ was mainly adsorbed on the vermiculite layer. In contrast, when mixture of vermiculite and palygorskite was packed at the ratio of 1:1, NH₄⁺ was mainly accumulated at the bottom of the column.     

Influence of nitrogen nutrition and metabolism on ammonia volatilization in plants

Barley (Hordeum vulgare L. cv. Golf) was grown in solution culture with controlled nitrogen availability in order to study the influence of nitrogen nutrition on ammonia emission from the leaves. Ammonia emission measured in cuvettes connected to an automatic NH₃ monitor was close to zero for nitrate grown plants but increased to 0.9–1.3 nmol NH₃ m^-2 leaf area s^-1 after 3–5 days of ammonium nutrition. Increasing concentrations from 0.5 to 10 mM NH₄ ⁺ in the root medium increased NH₃ emission from the shoots, root glutamine synthetase activity and NH₄ ⁺ concentrations in apoplast, xylem sap and bulk tissue, while apoplastic pH values decreased.Inhibition of glutamine synthetase in nitrate grown barley plants by addition of 1 mM methionine sulfoximine (MSO) to the root medium caused ammonia emission to increase 5 to 10-fold after 2–3 hours. At the same time shoot tissue ammonium concentrations started to increase. Addition of an inhibitor of photorespiration, 1 mM pyrid-2-yl hydroxymethane sulfonate (HPMS) reduced this increase in ammonia emission showing a relation between NH₃ emission and photorespiration.Oil seed rape (Brassica napus L. cv. Global) plants grown at 3 different nitogen levels (2N, 4N and 7N) in a sand/soil mixture showed increasing NH₃ compensation points with increasing N level. This increase was highly correlated with increasing NH₄ ⁺ concentrations in the leaf apoplast and total leaf tissue. The NH₃ compensation points could be succesfully predicted on basis of the pH and NH₄ ⁺ concentration in the leaf apoplast.     

Reconstruction of the Diaminopimelic Acid Pathway to Promote L-lysine Production in Corynebacterium glutamicum

The dehydrogenase pathway and the succinylase pathway are involved in the synthesis of L-lysine in Corynebacterium glutamicum. Despite the low contribution rate to L-lysine production, the dehydrogenase pathway is favorable for its simple steps and potential to increase the production of L-lysine. The effect of ammonium (NH₄⁺) concentration on L-lysine biosynthesis was investigated, and the results indicated that the biosynthesis of L-lysine can be promoted in a high NH₄⁺ environment. In order to reduce the requirement of NH₄⁺, the nitrogen source regulatory protein AmtR was knocked out, resulting in an 8.5% increase in L-lysine production (i.e., 52.3 ± 4.31 g/L). Subsequently, the dehydrogenase pathway was upregulated by blocking or weakening the tetrahydrodipicolinate succinylase (DapD)-coding gene dapD and overexpressing the ddh gene to further enhance L-lysine biosynthesis. The final strain XQ-5-W4 could produce 189 ± 8.7 g/L L-lysine with the maximum specific rate (q_Lys,max.) of 0.35 ± 0.05 g/(g·h) in a 5-L jar fermenter. The L-lysine titer and q_Lys,max achieved in this study is about 25.2% and 59.1% higher than that of the original strain without enhancement of dehydrogenase pathway, respectively. The results indicated that the dehydrogenase pathway could serve as a breakthrough point to reconstruct the diaminopimelic acid (DAP) pathway and promote L-lysine production.     

Optimizing ammonium adsorption on natural zeolite for wastewaters with high loads of ammonium and solids

Ion exchange (IE) has been so far limited to treating waters and wastewaters low in solids (TS) and ammonium (NH₄ ⁺). This study provides a new insight into the application of IE for NH₄ ⁺ removal from wastewaters with high NH₄ ⁺ and TS, using natural zeolite as adsorbent medium. Assays were carried out in continuously stirred batch reactors to study the effect of initial NH₄ ⁺, pH, TS, contact time, and zeolite pore size (0.2–0.5 and 0.6–2.0 mm). Results confirmed the suitability of this zeolite to remove NH₄ ⁺ from wastewater with high amounts of solids (up to 2%TS) and NH₄ ⁺ (up to 2500 mgNH₄ ⁺-N/L). Ammonium adsorption capacity (q _t ) was faster with 0.2–0.5 mm size because of the greater specific surface area and shorter diffusion path than 0.6–2.0 mm zeolite. Both zeolites showed increasing q _t with increasing initial NH₄ ⁺ due to the higher driving force produced by higher concentrations. The process followed a pseudo-second order kinetic and was best described by the Freundlich isotherm. Varying the pH (6–8.5) of the wastewater had no effect on NH₄ ⁺ removal capacity. In conclusion, this natural zeolite showed high affinity for NH₄ ⁺ in wastewater with high loads of NH₄ ⁺ and solids, returning a viable treatment method when other techniques are not applicable.     

Irrigation with Magnetized Water Alleviates the Harmful Effect of Saline–Alkaline Stress on Rice Seedlings

Saline–alkaline stress suppresses rice growth and threatens crop production. Despite substantial research on rice’s tolerance to saline–alkaline stress, fewer studies have examined the impact of magnetic water treatments on saline–alkaline-stressed rice plants. We explored the physiological and molecular mechanisms involved in saline–alkaline stress tolerance enhancement via irrigation with magnetized water using Nipponbare. The growth of Nipponbare plants was inhibited by saline–alkaline stress, but this inhibition was alleviated by irrigating the plants with magnetized water, as evidenced by greater plant height, biomass, chlorophyll content, photosynthetic rates, and root system in plants irrigated with magnetized water compared to those irrigated with non-magnetized water. Plants that were irrigated with magnetized water were able to acquire more total nitrogen. In addition, we proved that rice seedlings irrigated with magnetized water had a greater root NO₃⁻-nitrogen concentration and root NH₄⁺-nitrogen concentration than plants irrigated with non-magnetized water. These findings suggest that treatment with magnetized water could increase nitrogen uptake. To test this hypothesis, we analyzed the expression levels of genes involved in nitrogen acquisition. The expression levels of OsNRT1;1, OsNRT1;2, OsNRT2;1, OsAMT1;2, OsAMT2;1, OsAMT2;2, OsAMT2;3, OsAMT3;1, OsAMT3;2, and OsAMT3;3 were higher in plants exposed to magnetized water medium compared to those exposed to non-magnetized water media. We further demonstrated that treatment with magnetized water increases available nitrogen, NO₃⁻-nitrogen content, and NH₄⁺-nitrogen content in soil under saline–alkaline stress. Our results revealed that the increased resistance of rice seedlings to saline–alkaline stress may be attributable to a very effective nitrogen acquisition system enhanced by magnetized water.     

The effect of nitrification inhibitors on soil ammonia emissions in nitrogen managed soils: a meta-analysis

Nitrification inhibitors (NI) retain nitrogen (N) in the ammonium (NH₄ ⁺) form longer in soil providing more time for plant uptake of NH₄ ⁺. They can also reduce production of the greenhouse gas nitrous oxide (N₂O) by inhibiting nitrification and subsequent denitrification processes. However, this extended retention of N in the NH₄ ⁺ form in the soils treated with NI can increase ammonia (NH₃) emission. Studies conducted so far provide conflicting results on the effect of NI treatment on NH₃ emissions. Here we have collated results available to date from peer-reviewed literature (46 data set from 21 studies from 1970 to 2010) and categorized the reported results into three groups??increase, no change, and decrease in % applied N lost as NH₃ (hereafter NH₃ loss) in NI treatments. Significant increase in NH₃ loss in NI treatment was observed in both pasture and cropping soils and from both applied urine and urea with NI (e.g., dicyandiamide (DCD), ATC [4-amino- 1.2,4-triazole]). This increase in NH₃ loss was between 0.3 and 25.0?% (n?=?26, mean 6.7?±?standard error 1.3?%). No change in NH₃ loss with DCD was also observed in some soils (n?=?14), while a small number of studies reported a decrease which was between ?0.3 and ?4.1?% (n?=?6, ?1.3?±?0.6?%). Overall, the soils with higher pH and lower cation exchange capacity (CEC) lost more NH₃ with NIs irrespective of land use and type of N input. The combined addition of both NI and urease inhibitor reduced NH₃ loss compared to sole NI application (n?=?4, ?5.9?±?1.3?%). Collectively, the analysed results from the small number of available data sets reported suggest that NH₃ loss significantly increases with NI application, depending on soil properties such as soil pH and CEC. More studies are needed both to quantitatively determine the effect of NIs on NH₃ loss and to mitigate the loss.     

Reduction of nitrogen oxide on platinum electrodes in HClO4 and HCl

Reduction of NO in 2–8M HClO₄ and 2 M HCl at E ? 0.35V on platinized and smooth platinum electrodes is a diffusion-controlled process. On freshly activated electrodes the reduction in this potential region involves one-electron reaction to form N₂O, as well as multiple-electron reduction yielding NH₄⁺ and NH₃OH⁺. The product composition is largely dependent on the degree of electrode deactivation.     

Isotope Separation of Nitrogen by Ion Exchange Chromatography in a Cascade System

The ion exchange chromatography technique in a cascade process was used to separate stable isotopes of nitrogen (¹⁴N/¹⁵N). For this purpose, three column systems (with different internal diameters, S1?14.5 cm; S2–9.5 cm; S3–5.2 cm) were used that contained the cationic resins DOWEX 50 WX8 (as H⁺ and equilibrated with H₂O) and measured 1.7 m in height. Isotopic fractionation of nitrogen occurs during displacement band chromatography (DBC) of the NH₃ (aq) solution with a 0.75 mol L^?1 NaOH solution. The active sites of the resin were previously saturated to form NH₄ ⁺ (RNH₄) with a 0.75 mol L^?1 solution of (NH₄)₂SO₄ at a natural isotopic abundance (0.366 at. %) in ¹⁵N. The NH₄ ⁺/NH₃ (aq) equilibrium was determined during the DBC, which enriched the rear portion of the band with ¹⁵N. In S1, enrichment of approximately 5 at. % of ¹⁵N in the last 10 cm was achieved. After four interactions (couplings) between S1–S2, an enrichment of approximately 50 at. % of ¹⁵N was obtained. During the interaction between S2–S3, after the second coupling, an isotopic enrichment of approximately 90 at. % of ¹⁵N was observed, which produced 70 g month^?1 of (¹⁵NH₄)₂SO₄.     

Dinitrogen and methane gas production during the anaerobic/anoxic decomposition of animal manure

Trace-gas emissions from animal feeding operations (AFOs) can contribute to air quality and global change gases. Previous and current estimated gas emissions from AFOs vary widely and many do not consider all forms of carbon (C) and nitrogen (N) emissions. Studies have found that as methanogenesis in the lagoons increased, conversion of ammonium (NH₄ ⁺) to dinitrogen (N₂) also increased. The purpose of this research was to measure N₂ and CH₄ emissions from swine AFOs in three locations of the U.S. and to evaluate the possible universal relationship between lagoon methanogenesis and the conversion of NH₄ ⁺ to N₂ gas. This relationship was tested by measuring N₂ and CH₄ emissions in two climates at 22 different farms. Methanogenesis was correlated with NH₄ ⁺-to-N₂ conversion by a near-constant N₂ to CH₄ emissions ratio of 0.20, regardless of C loading and climatic effects. The process is shown to be thermodynamically favored when there is competition between NH₄ ⁺ oxidizing reactions. Under methanogenic conditions (redox potentials of methanogenesis) N₂ production is favorable and nitrification/denitrification is not. Thus, N₂ production is stimulated in methanogenic conditions. Evaluation of NH₃ gas emissions from AFOs must consider other N emissions than NH₃. Finally, a statistical model was developed to estimate methane and N₂ emissions (kg gas ha^?1) given feed input per lagoon surface area (kg feed ha^?1) and local air temperature. Further studies are needed to investigate the mechanisms involved in manure processing and isolate the favorable mechanisms into engineering improved manure processing.     

Effects of nitrogen fertilisers,calcium and water regime on the incidence of cavity spot in carrot

Two pot trials were conducted in the growth cabinet to examine the effects of rates and sources of nitrogen (N) fertilisers, rates of calcium (Ca), and two water regimes on the incidence of cavity spot in carrot (Daucus carota) roots. Treatments in Trial I included 4 rates (0, 100, 250, 500 kg N ha^?1) of sodium nitrate (NaNO₃), 4 rates (0, 460, 920, 1380 kg Ca ha^?1) of calcium carbonate (CaCO₃), and 2 water regimes (65 and 100% of the soil water-holding capacity). These treatments were repeated in Trial II, except that ammonium chloride (NH₄ Cl) + N-serve was used instead of NaNO₃. The incidence of cavity spot was found to increase significantly with increasing rates of NH₄Cl + N-serve applied, but not with NaNO₃ or CaCO₃ applications. The high water regime increased the incidence significantly only in Trial I. The results are discussed in relation to changes in soil NH ₄ ⁺ -N and NO ₃ ^- -N levels and other soil properties.     

Effect of hydroxyl and nitrate ions on the sorption of ammonium ions by sulphonic cation exchangers

The sorption of ammonium ions and ammonia by the H+ form of sulphonic acid cation exchangers Amberlite 252, Lewatit 2629 and Relite C 360 from a solution containing NH₄NO₃ in the range of 0 to 0.214 equ/L and NH₃ in the range of 0.353 to 0 equ/L was investigated to establish the possibility of their application for the recovery of ammonium from caustic condensate generated in nitrogen fertilizer production. Breakthrough and elution curves were obtained, determining the concentration of ammonium with Nessler's reagent. The sorption of ammonium and ammonia depends on the concentration ratio of ammonia to ammonium nitrate [NH₃]/[NH₄NO₃]. On decreasing [NH₃]/[NH₄NO₃], the concentration ratio of hydroxyl to nitrate ions [OH⁻]/[NO⁻₃] and the effluent pH prior to NH⁺₄ breakthrough also decrease. This results in a decrease in the NH⁺₄ sorption because of a deficiency in the neutralization of hydrogen ions released (ordinary cation-exchange process). Thus, adverse circumstances create an unfavorable medium for NH⁺₄ removal from the caustic condensate. Maximum sorption of NH⁺₄ is attained at [NH₃]/[NH₄NO₃] ∼1.2. A further decrease in [NH₃]/[NH₄NO₃] is followed by a significant decrease in the effluent pH, which leads to an increase in the concentration of protonated sulphonic acid groups (-SO₃H), resulting in a decrease in the ion-exchange ability of the cation exchangers under investigation with respect to NH⁺₄ removal. The concentration (g/L) of NH₄NO₃ in the eluate from the cation-exchanger regeneration, carried out using 0.7 bed volumes (BV) of 20% HNO₃, amounts to 136.7 for Relite C 360, 119.5 for Lewatit K 2629 and 96.7 for Amberlite 252. The content of undamaged beads after 100 cycles (each cycle comprises saturation with caustic condensate, containing ammonia and ammonium, successive regeneration with 20% nitric acid and washing) is from 97 to 99.8%. Resistance to boiling in 20% HNO₃ solution is from 97 to 99.8%. These are applicable for the recovery of NH₄NO₃ from the caustic condensate in the nitrogen fertilizers production, preventing economic damage and environmental contamination from nitrogen compounds.