Rate Of NO Research Articles

Applicability of a catalytic reduction method using a palladium–copper catalyst and hydrazine for the denitration of a highly concentrated nitrate salt solution

Denitration of a highly concentrated sodium nitrate (NaNO3) aqueous solution via a catalytic reduction method using a palladium–copper catalyst supported on carbon powder (Pd–Cu/C) and hydrazine (N2H4) was investigated. It was demonstrated that nitrate ion (NO3 −) in a 5 mol L−1 NaNO3 solution was completely reduced through an intermediate nitrite ion (NO2 −) to nitrogen compounds such as nitrogen, nitrous oxide, and ammonia. By comparing the reaction rates of NO3 − and NO2 − obtained using catalysts with various Pd–Cu compositions and different reductants (hydrogen (H2) or N2H4), it was determined that the catalyst with a molar ratio of Pd:Cu = 1:0.66 provides the maximum reaction rates for NO3 − and NO2 − using N2H4, and that not only the reactions of NO3 − and NO2 − but also that of N2H4 were affected by the Pd–Cu composition.

Pollutants Removal and Analysis of Microbial Community of Malodorous River in BFG-IVCWs

The changes of concentrations of pH, DO, CODCr, NH4+-N and NO3--N in Biofilm Grid-Integrated Vertical-flow Constructed Wetlands（BFG-IVCWs）by treating the urban malodorous river were measured. After 45 days, DO had its own distribution and changing regulation, the removal rate of CODCr reach to 45%, at meantime, the removal rate of NO3--N are over 50%. The diversity of microbial community and its succession were analyzed by PCR-DGGE fingerprint. The result shows: the removal rate of CODCr and NH4+-N along the river flow gradually rises, and the removal rate of NO3--N rises at last. The removal of pollutants mainly happened in the down-flow system of the BFG-IVCWs. The differences of characters of biofilm and environmental condition of different positions made the microbial community structure diversity variable. Three kinds of biofilms (W3, W5 and W7) were analyzed with Shannon-Wiener and Cs indices and the value in position W3 was the highest.

Effect of nitrate fertilization of gametophytes of the kelp Undaria pinnatifida on growth and maturation of the sporophytes cultivated in Matsushima Bay, northern Honshu, Japan

In northern Japan, the early production of high-quality specimens of kelps Undaria pinnatifida prior to the outbreak of pinhole disease is needed. To address this need, we tested the effect of nitrate fertilization of gametophytes on the growth and maturation of sporophytes using experimental and control gametophytes derived from sporophytes cultivated in Matsushima Bay, northern Honshu, Japan. From mid-August to October 2008, experimental gametophytes were cultured on a rope indoors at a nitrate concentration of 1 mg/L at the optimal seawater temperature of 20 °C, whereas control gametophytes were cultured without the addition of nitrate in normal seawater at an average temperature of 23.5 °C during this period in the past 30 years. Next, the seedlings were cultivated in Matsushima Bay until March 2009. For the experimental kelps, the total length, stipe length, stipe width, sporophyll length, sporophyll width, and dry weight of the blade, midrib, and sporophyll increased significantly from December to January compared to those of control kelps. Matured sporophylls of the experimental kelps were more than those of the control kelps from early December to late January. Significant higher photosynthesis occurred at seawater temperatures of 10 and 15 °C, as well as higher uptake rates of NO3–N of the experimental kelps in December and January. These results show that nitrate fertilization of the gametophytes makes it possible to harvest the high-priced blade, midrib, and sporophyll in January, which is earlier than the traditional harvest date.

Effects of Fertilizer Nitrogen on Short‐Term Nitrogen Loss in Bypass Flow in a Vertisol

Bypass flow, the vertical flow of free water along the walls of macropores or preferential flow paths in the soil, can lead to movement of fertilizer nutrients beyond the reach of plants. Fertilizer type and the rate of application, as well as the amount, frequency, and intensity of rainfall, can influence the amount of fertilizer nitrogen (N) loss in leaching or bypass flow. The effect of fertilizer N form and rate of application on N recovery in bypass flow in a Kenyan Vertisol was determined. Calcium nitrate and ammonium sulfate, used to supply nitrate (NO3 −)‐N and ammonium (NH4 +)‐N, respectively, were surface‐broadcast to 40‐cm‐long undisturbed soil columns at equivalent rates of 50, 100, and 200 kg N ha−1. Using a rainfall simulator, two rainfall events (30 mm of water applied in 1 h) were applied to the soil columns, one before and the other after fertilizer application. Total N, NO3 −‐N, and NH4 +‐N concentrations in the bypass flow were determined after the second rainfall event. The application of NH4 +‐N, regardless of the rate, had no effect on N recovery in the bypass flow. When nitrate N was applied, the amount of fertilizer N recovered in the bypass flow significantly increased with the rate of NO3 −‐N application. Of the total N in the bypass flow, 24 to 48% was derived from the soil, the bulk of which was organic N. It is concluded that following the application of NO3 −‐N, bypass flow is an important avenue of loss of both fertilizer and soil N from Vertisols.

‘Kardinal’ Rose Exhibits Growth Plasticity and Enhanced Nutrient Absorption Kinetics Following Nitrate, Phosphate, and Potassium Deprivation

Plant internal nutrient status is known to influence the kinetics of nutrient absorption, but little on this relationship has been reported for roses (Rosa spp. L.). The objectives of this experiment were to determine the influence of NO3, PO4, and K deprivation on plant tissue concentrations and relative growth rates and to quantify the influence of nutrient deprivation on absorption kinetic parameters. Rose plants growing in solution culture were deprived of N, P, or K for 0 to 20 days to establish differing tissue concentrations. Absorption kinetics were then determined based on the rate of NO3, PO4, or K depletion from solution over a range of concentrations. The data were fit to a modified Michaelis-Menten equation to account for the influence of internal nutrient status on absorption kinetics. Plants deprived of the nutrients for up to 20 d did not show significantly reduced root or plant fresh weight as compared with control plants. Plant tissue concentrations differed significantly by deprivation treatment and varied from 1.4% to 2.3% for N, 0.22% to 0.35% for P, and from 1.0% to 2.0% for K. Plants deprived of NO3, PO4, and K subsequently showed increased absorption rates. This was primarily expressed as an increased maximum absorption rate for NO3 and PO4. In contrast, K-deprived plants primarily exhibited an increased affinity (decreased Km) for K. The results demonstrate the plasticity of rose plants to grow and absorb nutrients under varying internal nutrient concentrations. This work quantifies the influence of rose plant nutritional status on the kinetics of NO3, PO4, and K absorption. The knowledge would be useful to improve models for providing decision support for fertilization based on plant growth rates and internal nutrient status.

Identifying plant species with root associated bacteria that promote nitrification and denitrification in ecological treatment systems

Plant-based systems, such as wetlands and other ecological treatment systems, are promising, sustainable alternatives to conventional wastewater treatment. One of the biggest drawbacks of these systems when compared with conventional wastewater treatment systems is a large land area requirement; thus greater efficiency is needed to reduce land requirements and consequent costs. This research identified plant species that promote greater nitrogen removal, and whose use could lead to increased efficiency of ecological treatment systems. Potential nitrification and denitrification rates of bacteria associated with the roots of herbaceous species (Cyperus papyrus, Colocasia esculentus), and woody species (Hibiscus moscheutus and Salix nigra) were measured in the lab. Potential nitrification rates were determined from the rate of NO 3 − accumulation in microcosms containing wastewater and live plants. Potential denitrification was measured using the acetylene inhibition technique on microcosm incubations of filtered wastewater and plant roots. Significantly more NO 3 − (mg 1−1 hr−1) was produced by bacteria associated with S. nigra and C. papyrus roots than in microcosms containing only wastewater, or H. moscheutus, (P < 0.001). Potential denitrification rates were significantly greater in H. moscheutos and S. nigra root microcosms than in C. esculentus and C. papyrus root microcosms on dry weight, wet weight and root area bases (P < 0.001). These results demonstrate that the efficiency of ecological treatment systems treating wastewater high in NH 4 + would be improved with a mix of herbaceous and woody species, whereas wastewater high in NO 3 − would be most efficiently treated with woody species. Thus, a diversity of species is needed to optimize ecological treatment system function.

Nitrate uptake at photic zone depths is not important for export in the subtropical ocean

Observations of nitrate (NO3−) uptake across the photic zone of the tropical and subtropical Atlantic Ocean are described. High NO3− uptake rates were commonly found at depth (&gt;75 m), coincident with the deep chlorophyll maximum and the nitracline, whereas highest rates of carbon fixation were found in near‐surface waters (0−50 m). Thus NO3− based estimates of in situ new production (NO3− uptake × 6.6) at depth are in excess of in situ measurements of carbon fixation implying NO3− uptake exceeds production requirements. Such surplus NO3− uptake may ultimately result in the production of dissolved organic nitrogen with its measurement within the particulate phase representing a transient enrichment. When only upper euphotic zone (to 14% irradiance depth) rates of NO3− uptake and carbon fixation are considered, new production is less than total carbon fixation, suggesting, as expected, that additional nitrogen sources are required to support the observed production levels. Comparison of the deep NO3− uptake rates with literature estimates of seasonal NO3− drawdown within the nitracline suggests that the drawdown observed represents only 1% of the actual NO3− uptake occurring in this region of the water column, and hence most NO3− uptake must be recycled locally rather than exported.

The Remarkable Effect of Oxygen on the N2 Selectivity of Water Catalytic Denitrification by Hydrogen

The selective catalytic reduction of nitrates (NO3-) in pure water toward N2 formation by the use of gaseous H2 and in the presence of O2 (air) at 1 atm total pressure and 25 degrees C has been investigated over Pd-Cu supported on various mixed metal oxides, x wt % MO(x(/gamma-Al2O3 (MO(x) = CeO2, SrO, Mn2O3, Cr2O3, Y2O3, and TiO2). It is demonstrated for the firsttime that a remarkable improvement in N2 reaction selectivity (by 80 percentage units) can be achieved when oxygen is present in the reducing feed gas stream. In particular, significantly lower reaction selectivities toward NH4+ and NO2- can be obtained, whereas the rate of NO3- conversion is not significantly affected. Moreover, it was shown thatthe same effect is obtained over the Pd-Cu-supported catalysts irrespective to the chemical composition of support and the initial concentration of nitrates in water used. The Pd-Cu clusters supported on 4.8 wt%TiO2/gamma-Al2O3 resulted in a solid with the best catalytic behavior compared with the rest of supports examined, both in the presence and in the absence of oxygen in the reducing feed gas stream. DRIFTS studies performed following catalytic reduction by H2 of NO3- in water revealed that the presence of TiO2 in the Pd-Cu/TiO2-Al2O3 system enhanced the reactivity of adsorbed bidentate nitrate species toward H2. Nitrosyl species adsorbed on the alumina and titania support surfaces are considered as active intermediate species of the selective catalytic reduction of NO3- by H2 in water. Pd-Cu/TiO2-Al2O3 appears to be the most selective catalyst ever reported in the literature for the reduction of nitrates present in pure water into N2 by a reducing gas mixture of H2/air.

Comparing Carbon Substrates for Denitrification of Subsurface Drainage Water

Nitrate in water from tile drained corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] fields in the U.S. Midwest contributes to nitrate contamination of surface waters. Denitrification-based biofilters are a promising strategy for reducing nitrate concentrations, but these systems require an external carbon supply to sustain denitrification. The ability of four organic materials to serve as carbon substrates for denitrification biofilters was evaluated in this laboratory study. Wood chips, wood chips amended with soybean oil, cornstalks, and cardboard fibers were mixed with subsoil (oxidized till) and incubated anaerobically for 180 d. Periodically, 15NO3-N was added to maintain nitrate N concentrations between 10 and 100 mg L-1. All of the materials stimulated NO3-N removal and the degree of removal from highest to lowest was: cornstalks, cardboard fibers, wood chips with oil, and wood chips alone. Analysis of 15N showed that immobilization and dissimilatory nitrate reduction to ammonium accounted for <4% of NO3-N removal in all treatments, therefore denitrification was the dominant NO3-N removal process. Cardboard fibers, wood chips and oil, and wood chips alone did not support as much denitrification as cornstalks, but their rates of NO3-N removal were steady and would probably continue longer than cornstalks. The addition of soybean oil to wood chips significantly increased denitrification over wood chips alone.

VARIATIONS OF CHEMICAL COMPOSITIONS IN COARSE AEROSOLS AND FINE AEROSOLS IN TWO SUCCESSIVE EPISODES

Particulate matter with diameters less than 2.5 microm (PM2.5) and ranging between 10 to 2.5 microm (PM10-2.5) were simultaneously collected at four air-quality monitoring stations in the Taichung area of central Taiwan during the period of February 12 to 22, 2004. Two different types of PM10 episodes, a nonlocal dust-storm episode and a local episode, were observed in the present study. High concentrations of coarse aerosols occurred during the dust-storm episode, whereas high concentrations of fine aerosols were present during the local episode. Relatively high levels of Na+, Mg2+, Ca2+, and Cl- in coarse aerosols were observed during the dust-storm episode. Very high concentrations of secondary aerosols (NH4+, SO4(2-), and NO3-) in fine aerosols were observed during the local episode. The nitrate ion demonstrated the greatest increase in the ratios of ionic species to PM2.5 and ionic species to PM10-2.5 during the local episode. Significantly high ratios (0.444) of NO3- to NO2 in fine aerosols were present during the local episode, indicating that the relatively high formation rate of NO3 was one of the important factors leading to the increase of the NO3 to PM2.5 ratio during the local episode. Results also showed that an abundant quantity of fine ammonium nitrate was formed during the local episode, and chloride depletion probably was the major pathway to form coarse NaNO3 during this episode.

The Potential for Nitrification and Nitrate Uptake in the Rhizosphere of Wetland Plants: A Modelling Study

It has recently found that lowland rice grown hydroponically is exceptionally efficient in absorbing NO3-, raising the possibility that rice and other wetland plants growing in flooded soil may absorb significant amounts of NO3- formed by nitrification of NH4+ in the rhizosphere. This is important because (a) this NO3- is otherwise lost through denitrification in the soil bulk; and (b) plant growth and yield are generally improved when plants absorb their nitrogen as a mixture of NO3- and NH4+ compared with growth on either N source on its own. A mathematical model is developed here with which to assess the extent of NO3- absorption from the rhizosphere by wetland plants growing in flooded soil, considering the important plant and soil processes operating. The model considers rates of O2 transport away from an individual root and simultaneous O2 consumption in microbial and non-microbial processes; transport of NH4+ towards the root and its consumption in nitrification and uptake at the root surface; and transport of NO3- formed from NH4+ towards the root and its consumption in denitrification and uptake by the root. The sensitivity of the model's predictions to its input parameters is tested over the range of conditions in which wetland plants grow. The model calculations show that substantial quantities of NO3- can be produced in the rhizosphere of wetland plants through nitrification and taken up by the roots under field conditions. The rates of NO3- uptake can be comparable with those of NH4+. The model also shows that rates of denitrification and subsequent loss of N from the soil remain small even where NO3- production and uptake are considerable. Nitrate uptake by wetland plants may be far more important than thought hitherto. This has implications for managing wetland soils and water, as discussed in this paper.

Atmospheric dry deposition in the vicinity of the Salton Sea, California—I: Air pollution and deposition in a desert environment

Abstract Air pollutant concentrations and atmospheric dry deposition were monitored seasonally at the Salton Sea, southern California. Measurements of ozone (O3), nitric acid vapor (HNO3), ammonia (NH3), nitric oxide (NO), nitrogen dioxide (NO2) and sulfur dioxide (SO2) were performed using passive samplers. Deposition rates of NO3−, NH4+, Cl−, SO42−, Na+, K+ and Ca2+ to creosote bush branches and nylon filters as surrogate surfaces were determined for one-week long exposure periods. Maximum O3 values were recorded in spring with 24-h average values of 108.8 μg m−3. Concentrations of NO and NO2 were low and within ranges of the non-urban areas in California (0.4–5.6 and 3.3–16.2 μg m−3 ranges, respectively). Concentrations of HNO3 (2.0–6.7 μg m−3) and NH3 (6.4–15.7 μg m−3) were elevated and above the levels typical for remote locations in California. Deposition rates of Cl−, SO 4 2 – , Na+, K+ and Ca2+ were related to the influence of sea spray or to suspended soil particles, and no strong enrichments caused by ions originated by human activities were detected. Dry deposition rates of NO 3 – and NH 4 + were similar to values registered in areas where symptoms of nitrogen saturation and changes in species composition have been described. Deposition of nitrogenous compounds might be contributing to eutrophication processes at the Salton Sea.

Effects of defoliation and atmospheric CO2 depletion on nitrate acquisition, and exudation of organic compounds by roots of Festuca rubra

The aim of this study was to investigate the physiological basis of increased root exudation from Festuca rubra, in response to defoliation. The hypothesis, that assimilate supply to roots is a key determinant of the response of root exudation to defoliation was tested by imposing CO2-deplete (< 50 μmol mol−1) atmospheres to F. rubra. This was done as a non-destructive means of preventing supply of new assimilate to roots of intact and defoliated plants. F. rubra was grown in axenic sand systems, with defoliation and CO2-depletion treatments applied to plants at 14 and 35 days after planting. Root exudation and NO3 − uptake were quantified throughout, and post-treatment uptake and allocation of N were determined from the distribution of 15N label, supplied as 15NO3 −. Defoliation of F. rubra resulted in significantly (P <0.01) increased root exudation, CO2-depletion did not result in increased exudation from plants of either age. When treatments were applied to F. rubra after 14 days, defoliation and CO2-depletion each reduced NO3 − uptake significantly (P <0.05). However, in older plants, uptake of NO3 − was less sensitive to defoliation and CO2-depletion. The results indicate that increased root exudation following defoliation is not related directly to reduced assimilate supply to roots. This was evident from the lack of effect of CO2-depletion on root exudation, and the absence of correlation between root-C efflux and the rate of NO3 − uptake. The physiological basis of increased exudation following defoliation remains uncertain, but may be dependent on physical damage, either directly or as a consequence of systemic responses to wounding.

REGULATION OF NITRIC OXIDE EMISSIONS FROM FOREST AND RANGELAND SOILS OF WESTERN NORTH AMERICA

Nitric oxide (NO) is a relatively short-lived trace gas that reacts with oxygen in the troposphere to produce the air pollutant ozone. It also reacts with water vapor to form nitric and nitrous acids, which acidify precipitation and increase N deposition. Models currently used to predict soil NO fluxes are based on the assumption that NO flux is proportional to the gross rate of nitrification or N mineralization; however, this assumption has not been tested because of the difficulty in measuring gross N-cycling rates in situ. We measured soil NO fluxes, gross and net N-cycling rates, and a variety of other soil char- acteristics in the forest floor and intact soil cores at nine undisturbed forest and rangeland ecosystems of New Mexico, Utah, and Oregon, USA, to determine which soil variables were most closely related to soil NO flux. Soil NO fluxes ranged from a low of 0.02 ng N·m 22 ·s 21 , prior to wetting in a western hemlock-sitka spruce forest on the Oregon coast, to a high of 6.74 ng N·m 22 ·s 21 , one hour after soil wetting in a juniper woodland of central Oregon. In contrast to our expectations, neither gross nitrification nor gross mineralization was correlated with soil NO flux. Fluxes were positively correlated with net rates of min- eralization and nitrification, soil NO3 2 concentrations, bulk density, and pH, and negatively correlated with gross rates of NO3 2 consumption in the forest floor, soil organic carbon (SOC), soil C:N, and soil water content. Principal-component analysis showed that NO flux after water addition (2 cm of water) had a strong negative correlation with microbial demand for N (as indicated by net mineralization, net nitrification, SOC, and C:N). Our results suggest that, even in well-drained soils, NO efflux is limited more by NO con- sumption than by NO production. As a result, models utilizing the more easily measured net rates, rather than gross rates, may be better predictors of soil NO fluxes across a range of ecosystems.

Regulation of Nitric Oxide Emissions from Forest and Rangeland Soils of Western North America

Nitric oxide (NO) is a relatively short-lived trace gas that reacts with oxygen in the troposphere to produce the air pollutant ozone. It also reacts with water vapor to form nitric and nitrous acids, which acidify precipitation and increase N deposition. Models currently used to predict soil NO fluxes are based on the assumption that NO flux is proportional to the gross rate of nitrification or N mineralization; however, this assumption has not been tested because of the difficulty in measuring gross N-cycling rates in situ. We measured soil NO fluxes, gross and net N-cycling rates, and a variety of other soil characteristics in the forest floor and intact soil cores at nine undisturbed forest and rangeland ecosystems of New Mexico, Utah, and Oregon, USA, to determine which soil variables were most closely related to soil NO flux. Soil NO fluxes ranged from a low of 0.02 ng N·m−2·s−1, prior to wetting in a western hemlock–sitka spruce forest on the Oregon coast, to a high of 6.74 ng N·m−2·s−1, one hour after soil wetting in a juniper woodland of central Oregon. In contrast to our expectations, neither gross nitrification nor gross mineralization was correlated with soil NO flux. Fluxes were positively correlated with net rates of mineralization and nitrification, soil NO3− concentrations, bulk density, and pH, and negatively correlated with gross rates of NO3− consumption in the forest floor, soil organic carbon (SOC), soil C:N, and soil water content. Principal-component analysis showed that NO flux after water addition (2 cm of water) had a strong negative correlation with microbial demand for N (as indicated by net mineralization, net nitrification, SOC, and C:N). Our results suggest that, even in well-drained soils, NO efflux is limited more by NO consumption than by NO production. As a result, models utilizing the more easily measured net rates, rather than gross rates, may be better predictors of soil NO fluxes across a range of ecosystems.

Preparation and Photoactive Characterization of Tube-shaped Al-doped ZnO Ceramics.

ABSTRUCT:Tubular Al-doped ZnO particles were prepared by homogeneous precipitation in the mixed solutions of Al(NO3)2, Zn(NO3)2, sodium dodecyl sulfate (SDS) surfactant and urea. At the molar ratio of Metal ions(Mt) : SDS : urea : H2O is 1 : 2 : 20 : 60, tubular products formed by heating at 80°C for 12 h. Plate like ZnO particles were obtained at Mt : SDS : urea : H2O = 1 : 2 : 10 : 60 or 1 : 1 : 20 : 60. The diameter of typical ZnO tube is ca.100 nm, and the length of tube is about 600nm (aspect ratio = 6). The relative surface area of tubular Al-doped ZnO is ca. 40.2 m2/g. The photo-decomposition rate of NO3- ions using tubular Al-doped ZnO particles was higher than standard TiO2 photo-catalysts (P-25) by irradiation &gt;290nm light in 10mM KNO3-10vol%EtOH solutions at 30°C. The obtained materials showed DC conductive properties as compacted substrate by sintered at 400°C.

COMPARISONS OF NITRATE UPTAKE, STORAGE, AND REDUCTION IN MARINE DIATOMS AND FLAGELLATES

Diatoms, but not flagellates, have been shown to increase rates of nitrogen release after a shift from a low growth irradiance to a much higher experimental irradiance. We compared NO3− uptake kinetics, internal inorganic nitrogen storage, and the temperature dependence of the NO3− reduction enzymes, nitrate (NR) and nitrite reductase (NiR), in nitrogen‐replete cultures of 3 diatoms (Chaetoceros sp., Skeletonema costatum, Thalassiosira weissflogii) and 3 flagellates (Dunaliella tertiolecta, Pavlova lutheri, Prorocentrum minimum) to provide insight into the differences in nitrogen release patterns observed between these species. At NO3− concentrations &lt;40 μmol‐N·L−1, all the diatom species and the dinoflagellate P. minimum exhibited saturating kinetics, whereas the other flagellates, D. tertiolecta and P. lutheri, did not saturate, leading to very high estimated K s values. Above ∼60 μmol‐N·L−1, NO3− uptake rates of all species tested continued to increase in a linear fashion. Rates of NO3− uptake at 40 μmol‐N·L−1, normalized to cellular nitrogen, carbon, cell number, and surface area, were generally greater for diatoms than flagellates. Diatoms stored significant amounts of NO3− internally, whereas the flagellate species stored significant amounts of NH4+. Half‐saturation concentrations for NR and NiR were similar between all species, but diatoms had significantly lower temperature optima for NR and NiR than did the flagellates tested in most cases. Relative to calculated biosynthetic demands, diatoms were found to have greater NO3− uptake and NO3− reduction rates than flagellates. This enhanced capacity for NO3− uptake and reduction along with the lower optimum temperature for enzyme activity could explain differences in nitrogen release patterns between diatoms and flagellates after an increase in irradiance.

Photoreduction of NO3 − and NO2 − under Visible Light Irradiation with Layered H4Nb6O17/CdS and H2Ti4O9/CdS Nanocomposites

The photoreduction of NO3 − and NO2 − was performed at 60 °C under irradiation of visible light (λ > 400 nm) in the presence of unsupported CdS, H4Nb6O17/CdS and H2Ti4O9/CdS in 10 vol.% aqueous methanol solution. The photoreduction rate of NO3 − proceeded in the presence of H4Nb6O17/CdS and H2Ti4O9/CdS nanocomposites although unsupported CdS, H4Nb6O17/CdS and H2Ti4O9/CdS did not show photocatalytic activity for nitrate reduction under visible light irradiation. The photoreduction rate of NO3 − and NO2 − changed significantly depending on solution pH, i.e., with increasing solution pH the reduction rate of NO3 − increased, on the orther hand, that of NO2 − decreased.

Nitrate transport processes in Fagus-Laccaria-Mycorrhizae

The contribution of influx and efflux of NO3 - on NO3 - net uptake has been studied in excised mycorrhizae of 18–20 week old beech (Fagus sylvatica L.) trees. Net uptake rates of NO3 - followed uniphasic Michaelis-Menten kinetics in the concentration range between 10 μM and 1.0 mM external NO3 -, with an apparent Km of 88±7 μM, and a Vmax of 110±7 nmol g-1 root f.wt. h-1. The relative xylem loading of N, i.e. the portion of NO3 - taken up that was loaded into the xylem vessels as NO3 - plus reduced N, was constant over the concentration range tested (4.6–7.7%). NO3 - influx proceeded linearly with increasing external NO3 - supply. When the assumed regulators of net NO3 - uptake, i.e. NH4 + or L-glutamate, were applied together with NO3 -, net uptake rates of NO3 - decreased. This inhibitory effect was caused by a reduction of NO3 - influx rather than an enhanced efflux. The comparison of the present data with a recent study with non-mycorrhizal beech roots (Kreuzwieser et al., 1997; J. Exp. Bot. 48, 1431–1438) revealed that mycorrhization leads to reduced rates of NO3 - net uptake. This effect is caused by reduced influx plus enhanced efflux of NO3 - as compared with non-mycorrhizal beech roots.

Nitrogen and base cation uptake in seedlings of Acer pseudoplatanus and Calamagrostis villosa exposed to an acidified environment

The effects of solution acidity and form of nitrogen on net nutrient uptake rates in Acer pseudoplatanus and Calamagrostis villosa seedlings were examined as part of a complex ecological study. Uptake rates were measured by the depletion method under controlled conditions (temperature 20 °C, irradiance 400 µmol m−2 s−1 PAR) from a nutrient solution containing 1.5 mM nitrogen in the form of nitrate or ammonium or an equimolar mixture of both. The solution acidity was kept constant at pH 5.5 (control treatment), 4.5 or 3.5 (low pH treatments). Strongly acid pH decreased or stopped the uptake rates of NO3−, Mg2+ and Ca2+, but the uptake of NH4 + was not changed in both species Ammonium ions reduced the uptake rate of NO3 − in Acer but increased the uptake rate in Calamagrostis Ammonium as the sole source of nitrogen had a strong negative impact on the uptake rates of calcium and magnesium and this effect was independent of the media acidification usually connected with NH4 + uptake and assimilation. However, the negative effect of ammonium ions on the base cation uptake was more pronounced at low pH values.