Amount Of NH Research Articles

In situ changes in gross N transformations in bare soil after addition of straw

In situ 15N techniques were used to quantify gross mineralisation, immobilisation and nitrification of N in bare soil nonamended and after incorporation of wheat straw (8 t ha −1). Experimental plots were confined within open-ended cylinders inserted into the tilled layer to 20 cm depth of a loamy soil (Typic Hapludalf). Measurements of gross N fluxes and C mineralisation were made during the year following incorporation of residues (September 1993–October 1994). At each date of measurement, inorganic N was added to soil by multiple injections of 15NH 4 15NO 3 (atom % excess=50.0) to a soil depth of 17.5 cm. The amount of NH 4 +-N, NO 3 −-N, organic N and their 15N isotopic composition were determined 30 min after 15N injections ( t 0), and 2–3 d after in situ incubation ( t 1). N transformation rates were estimated using a numerical model, Fluaz. In the nonamended soil, gross mineralisation in the 0–20 cm layer varied between 0.23 mg N kg −1 soil d −1 in December and 0.81 mg N kg −1 soil d −1 in July. Immobilisation rate varied similarly and was about one-third of gross mineralisation. Gross fluxes corrected for the effects of soil temperature and water content, and expressed as a function of normalised time (day at 10°C and optimal water potential) varied much less. The mean rate of gross mineralisation was 0.42 mg N kg −1 soil normalised d −1, and for immobilisation it was 0.13 mg N kg −1 soil normalised d −1, resulting in net mineralisation of 0.29 mg N kg −1 soil normalised d −1. Gross mineralisation and immobilisation were both increased by straw addition, with rates of 0.99 and 1.98 mg N kg −1 soil d −1 respectively, observed for the first measurement in September, 7 d after incorporation. Immobilisation and mineralisation decreased steadily with time. One year after straw addition, gross immobilisation and mineralisation rates were similar to those measured in nonamended soil. This was consistent with the changes in rate of straw-C mineralisation and with the depletion of the coarse fraction in soil, determined in parallel.

EVALUATION OF COMPACTED UREA FERTILIZERS PREPARED WITH ACID AND NON-ACID PRODUCING CHEMICAL ADDITIVES IN THREE SOILS VARYING IN PH AND CATION EXCHANGE CAPACITY. I. NH3 VOLATILIZATION

Efficacy of different acid-producing chemical additives was evaluated in terms of pH, urea hydrolysis, NH4-N dynamics and NH3 volatilization in an Alfisol, a Vertisol and an Inceptisol. Compacting phosphogypsum (PG), diammonium phosphate (DAP), ZnSO4 and KCl separately with urea slowed down urea hydrolysis and reduced NH3 volatilization loss. Peak volatilization loss of NH3 occurred between 2 to 4 days of fertilizer application in Vertisol and Alfisol, but between 4 to 6 days in Inceptisol. Cation exchange capacity (CEC) of soil influenced more in reducing NH3 loss than native soil pH, as lower amount of NH3 was lost from Vertisol (pH=8.0, CEC=43.92 cmolc kg-1) than from Alfisol (pH=5.8, CEC=13.82 cmolc kg-1). The loss from Inceptisol was in between the above two soils.

Tg/dta, Xrd and NH3-TPD Characterization of Layered VOPO4·2H2O and its Fe3+-Substituted Compound

Iron(III)-substituted vanadyl phosphate, [Fe(H2O)]0.20VO0.80PO4·2.25H2O (FeVOP), has been prepared and characterized by XRD and TG/DTA analyses. The new compound is isomorphous with layered tetragonal VOPO4·2H2O (VOP), but it possesses a lower interlayer distance. Information on the reactivity and surface acidity of both VOP and FeVOP has been obtained by NH3-TPD experiments. The hydrated materials adsorb high amounts of NH3 (up to 2 mmol g-1). Different ammonia-containing phases are formed, characterized by lower interlayer distances in comparison with the NH3-free parent compounds. NH3 is intercalated between the layers without displacement of water. The materials dehydrated by heat treatment at 450°C retain the layered structure but adsorb NH3 only on the external surface. A wide variety of acid sites, from weak to strong, was observed. A mechanism is proposed for the NH3- acid sites interaction. SEM micrographs of VOP and FeVOP are shown.

Competitive solvation of NH 3 and H 2O by a phenol ion studied by liquid beam — multiphoton ionization — mass spectrometry

Phenol in an aqueous ammonia solution was introduced into a vacuum as a continuous liquid flow (liquid beam) and was irradiated with a laser beam of 272 nm. Ions produced by two-photon ionization in the liquid beam and ejected from it were analyzed by a time-of-flight mass spectrometer. The mass spectrum assignable to C 6H 5OH + (H 2O) n (NH 3) m , H 3O + and NH 4 + shows that a phenol ion produced by two-photon ionization or a protonated ion produced by proton transfer from the phenol ion is ejected with several solvent molecules from the liquid surface, and the nascent cluster ion decays by unimolecular dissociation before detection. The amount of NH 3 in the nascent cluster ion at different NH 3 mole fractions is evaluated from that of the ions detected by taking its unimolecular dissociation into consideration. The results show that the phenol ion solvates NH 3 more favorably than H 2O in the solution.

Determination of the content and distribution of fixed ammonium in illite-smectite by X-ray diffraction; application to North Sea illite-smectite

A new X-ray diffraction method for the determination of the amount and distribution of fixed NHt in illite-smectite has been developed. Illite-smectite was saturated with K+ and heated at ISO °C. The 002 and 005 reflections were recorded with steps of 0.01028, and the experimental d values and the values for full-width at half-height (FWHH) were determined using a peak-profile-fitting procedure. Peak profiles were calculated with the NEWMOD program for illite structures having different amounts of NH: and different patterns for the distribution of NH: in interlayers. For Upper Jurassic illite-smectite from North Sea oil source rocks, the amount and the distribution of NH: in illite interlayers were determined by comparing the experimental values for doo5 and FWHH with the values calculated for the selected illite structures. The amounts of NH: determined in this manner correlate well with the amounts determined by an isotopic dilution method. The results demonstrate that these illite-smectite samples have K end-member illite and NH4 endmember illite (tobelite) layers and that the illite layers formed during diagenesis and oil generation actually are tobelite layers.

Indices of plant N availability in an alpine grassland under elevated atmospheric CO2

The objective of this study was to estimate whether elevated atmospheric [CO2] alters plant N availability in a native high-elevation grassland in the Swiss Alps using two integrative, relatively non-disruptive methods. Estimates based on seasonal net plant N uptake, and those based on the amounts of NH 4 + -N plus NO 3 − -N captured by ion exchange resin (IER) bags, did not differ in plots treated with ambient (355 μL L−1) and elevated (680 μL L−1) [CO2] in either the second (1993) or third (1994) growing season under treatment with elevated [CO2]. The results of this study suggest that the effects of rising atmospheric [CO2] on plant N availability may be negligible in this grassland. The results also contrast the relatively large effects of elevated atmospheric [CO2] (increases and decreases) reported for highly disturbed artificial systems.

Nitrogen acquisition and competitive ability of Kalmia angustifolia L., paper birch (Betula papyrifera Marsh.) and black spruce (Picea mariana (Mill.) B.S.P.) seedlings grown on different humus forms

Two species of boreal tree seedlings, paper birch (Betula papyrifera Marsh.) and black spruce (Picea mariana (Mill.) B.S.P.), and the ericaceous shrub Kalmia angustifolia L. were grown in pots with humus from a birch-dominated site and two spruce-Kalmia sites. Root systems interacted with humus form in controlling soil-N cycling as well as energy and nutritional deficiencies of soil microorganisms. In general, Kalmia seedlings affected microbial dynamics and N cycling differently than birch and spruce seedlings did. Birch and spruce seedlings reduced gross N mineralization and immobilization rates, soil mineral-N pools and the amounts of NH\(_4^ + \)–N accreted on buried cation exchange resins in all three soils. Compared to birch and spruce seedlings, the growth of Kalmia resulted in significantly higher gross N mineralization rates, soil mineral-N pools and resin-NH\(_4^ + \) accretion in soil from the fertile birch site. Gross N immobilization rates in all soils were generally higher with Kalmia than with spruce or birch seedlings. All three species of seedlings acquired N from the birch site soil, whereas only Kalmia seedlings acquired N from the two spruce-Kalmia site soils. Relative to control treatments, the amount of N mineralized anaerobically increased in the birch-site soil and decreased in the poor spruce-Kalmia site soil with all three species of seedlings. All seedlings increased the microbial biomass in the birch-site soil. Kalmia humus and Kalmia root systems increased microbial energy-deficiency and decreased microbial nutritional deficiency compared to the other humus and seedlings used. Results are discussed in terms of each species' nutrient acquisition mechanism and its competitive ability during secondary succession.

Influence of spatial root distribution, organic nitrogen mineralization and fertilizer application on soil interlayer ammonium

The amount of interlayer NH 4 + -N and net mineralization of organic N were measured at periodic intervals, over a period of 10 months, in soil samples collected from a peach orchard which had been subjected to different rates of N fertilizer application. Two different groups of soil samples, designated sampling 1 and sampling 2 were collected. Soils of sampling 1 were collected from sites where the soil was heavily penetrated by tree roots and those of sampling 2 were collected from sites where the soil remained free from tree roots. In sampling 1, during the 10-month period, the concentration of interlayer NH 4 + -N showed significant variations, while in sampling 2 no significant variation was found. In sampling 1 the amount of NH 4 + -N released from the interlayers of the clay minerals were not influenced by the N fertilizer application rate. Changes in the interlayer NH 4 + -N concentrations were related to variation in net N mineralization and immobilization rates as well as to plant uptake N. It is concluded that, in our experiment, the dynamics of interlayer NH 4 + -N in soil were influenced by the spatial distribution of the tree roots and organic N mineralization, while N application influenced seasonal variation but not the total interlayer NH 4 + -N released during the experiment.

Solution, exchangeable and clay-fixed ammonium in south coast British Columbia soils

Solution, exchangeable and clay-fixed ammonium were measured in a variety of south coast British Columbia soils in the laboratory using extraction, equilibration and leaching procedures, and with and without ammonium amendments in order to evaluate the relative significance of adsorption and fixation processes on nitrogen behavior. Non-amended soils contained from 59 to 224 g N g−1 of fixed ammonium and these amounts were correlated with clay (positive) and sand (negative) contents. The amount of native fixed ammonium in the soils was influenced by management history. Recovery of ammonium added to eight selected samples by a small volume of solution followed by air drying was the same with 1 and 2 M KCl extractions, but less was extracted by 0.1 M KCl and even less by water. This showed that both 1 and 2 M KCl had sufficient K+ to displace the NH4+ present (inherent and added) on the exchange sites without an apparent effect on fixed ammonium. Up to 68% of the ammonium added was not extracted by 2 M KCl and assumed to have been fixed in the clay lattice. The proportion of the added ammonium that was adsorbed onto the exchange sites was linear up to 200 μg N g−1 application, but the amount fixed by the clays was linear to only about 100 μg N g−1 application rate. Data from studies where soil columns were leached with NH4NO3 provided only limited information on the relative importance of exchange versus fixation processes to the adsorption of ammonium. Leaching columns with a limited number of batches of NH4NO3 followed by water (short cycle) were useful for comparing the ability of different soils to adsorb and retain ammonium, but the relative importance of exchange versus fixation could not be determined. In the 18 samples of this study, the amount of NH4+ adsorbed ranged from 84 to 25% during short cycle column leachings. Different patterns of adsorption occurred among the four soil samples that were leached with a large number of batches of ammonium (long cycle), but it could not be determined whether or not these patterns were related to differences in proportions of fixation relative to exchange. Measurements showed that ammonium was fixed in the soils during the long cycle leachings but that the amounts of fixed ammonium measured were influenced by air drying the sample before analysis. Several studies with and without toluene additions showed that microbial activity must be controlled during these measurements. It was concluded that south coastal soils contained significant amounts of fixed ammonium and can fix additional ammonium. The amount of ammonium in the clay fixed pool and the potential to fix added ammonium was different in relation to the soil type, their previous management, and wetting and drying cycles. The biological significance of fixed ammonium and the fixation process must not be discounted in any nitrogen studies of these soils for proper interpretation of data. Key words: Ammonium fixation, equilibration, column leaching, microbial/enzyme inhibition, extractant concentration

Methane emission from a landfill and the methane oxidising capacity of its covering soil

Methane emission from a small covered landfill site showed, seasonally varying fluxes, ranging from −5.9 to 914.3 mg CH 4 m −2 d −1. The moisture content of the CH 4-oxidising cover soil was thought to cause this variation. Comparing gross and net CH 4 emission rates, it was found that the cover soil, due to its CH 4 oxidising capacity, had a large mitigating effect on the CH 4 emission. In laboratory experiments the effects of soil moisture, temperature and different ammonium amendments on CH 4 oxidation were investigated. When the moisture content and temperature were combined, CH 4 oxidation rates between 0.88 and 10.86 ng CH 4 g −1 h −1 were observed. The optimum moisture content ranged between 15.6 and 18.8% w/w ( ±1 2 WHC ). The optimum incubation temperature (30-20°C) decreased with increasing moisture contents. For the oxidation rates at 10 and 20°C, we found an average Q 10 value of 1.88 ± 0.14. The activation energy for moisture contents between 5 and 25% was 83.0 ± 4.4 kJ mol −1. Increased ammonium additions reduced the CH 4-oxidising capacity. This reduction decreased with increasing moisture contents. A high correlation (R 2 > 0.98) was found between the moisture content and the reduction of the CH 4 uptake rate mg −1 NH 4 + −N kg −1 added. Because the nitrification rate was also lower at higher moisture contents, it was thought that the CH 4 oxidation rate was more closely connected with the NH 4 + turnover rate than with its actual concentration. Multiple linear regression analysis of the CH 4 oxidation rates under the different incubation conditions showed the following decreasing effect on the CH 4-oxidising capacity of the soil: amount of NH 4 + added > moisture content > incubation temperature.

Effects of Terbuthylazine on Soil Fauna and Decomposition Processes

Acute lethal and sublethal effects of terbuthylazine and the commercial herbicide preparation Gardoprim [terbuthylazine is the active ingredient (a.i.)] on soil organisms (microbes, oppioid mites, two gamasid mite species, enchytraeids, and nematodes) were studied. In the humus soil terbuthylazine had no toxic effects on soil animals tested. However, the herbicide preparation had acute toxic effects on enchytraeids [no-observed-effect level (NOEL) 1.0 g a.i./m2] and both gamasid mites (NOEL 2.4 and 5.0 g a.i./m2). According to filter paper test, the LC50value for oppioid mites was 14.5 g a.i./m2. In the humus soil the commercial preparation caused no dose-related mortality in Oppioidea. The preparation was more toxic to gamasid mites when the herbicide was applied on the soil surface compared to the treatment in which the chemical was mixed into the humus. Application method of the chemical did not affect the mortality of enchytraeids. In the multispecies experiment, the number of nematodes was higher in the highest concentration of the commercial preparation (50 g a.i./m2) compared to the lowest concentration (1 g a.i./m2) and the clean soil. The amount of NH+4–N in the humus tended to increase with increasing herbicide concentration. The herbicide did not affect soil respiration, microbial biomass, or water content of the humus. These results indicated that herbicides can have direct effects on soil fauna. Due to species-specific foraging strategies or different exposure routes and rates to animals, effects of herbicides on soil animals varied considerably. Single-species toxicity tests performed in humus soil were more sensitive to the effects of herbicide than ecologically relatively short-term multispecies test.

Photodegradation of surfactants XIV. Formation of NG 4+ and NO 3− ions for the photocatalyzed mineralization of nitrogendashcontaining cationic, nondashionic and amphoteric surfactants

The photo-oxidation of cationic, nondashionic and amphoteric nitrogendashcontaining surfactants ( ndashdodecylpyridinium chloride (DPC) and benzyl-tetradecyldimethyl-ammonium chloride (BTDAC); dodecanoyl- ndash(2-hydroxyethyl) amide (ndashDHA) adn dodecanoyl- N, ndashbis(2 hydroxyethyl) amide (N,ndashDHA); dodecyl-β-alanine (C 12-β-Ala) and ndash(2-hydroxydodecyl)- ndash(2-hydroxyethy)- β-alanine (C 12-βHAA)) was examined in UV-illuminated, air-equilibrated aqueous titania suspensions. Variations in the surface tension of the photo-oxidized surfactant solutions were monitored as a function of the irradiation time. The formation of ammonium and nitrate ions, together with the evolution of carbon dioxide, was investigated for the various surfactant chemical structures to obtain mechanistic information on the mineralization pathways. The yield of NH 4 + ions was 4–13 times greater than yield of NO 3 + ions. The amount of NH 4 + ions formed depends on the structures of the surfactants. Mechanistic details of the photocleavage of the alkyl chains were inferred by probing the oxidation of sodium dodecanoate. The intermediates formed during the temporal photomineralization of the surfactant species were identified by high-frequency Fourier transform (FT) proton nuclear magnetic resonance (NMR) spectroscopy.

Ammonium assimilation in rice based on the occurrence of15N and inhibition of glutamine synthetase activity

Abstract Assimilation of ammonium (NH4) into free amino acids and total reduced nitrogen (N) was monitored in both roots and shoots of two‐week old rice seedlings supplied with 5 mM 99% (15NH4)2SO4 in aerated hydroponic culture with or without a 2 h preincubation with 1 mM methionine sulfoximine (MSX), an inhibitor of glutamine synthetase (GS) activity. 15NH4 was not assimilated into amino acids when the GS/GOGAT (glutamate synthase) cycle was inhibited by MSX. Inhibition of glutamine synthetase (GS) activity in roots with MSX increased both the amount of NH4 and the abundance of 15N labeled NH4. In contrast, the amount of Gln and Glu, and their proportions as 15N, decreased in roots when GS activity was inhibited. This research confirms the importance of GS/GOGAT in NH4 assimilation in rice roots. 15N‐labeled studies indicate that NH4 ions incorporated by roots of rice are transformed primarily into glutamine (Gln) and glutamic acid (Glu) before being converted to other amino acids through transamination...

Geographical variability in the bioenergetic characteristics of Monoporeia/Pontoporeia spp. populations from the northern Baltic Sea, and their potential contribution to benthic nitrogen mineralization

The physiological condition, determined as the ammonia excretion rate (V NH4+), total lipid level and lipid class composition, of two deposit-feeding benthic amphipods, Monoporeia (=Pontoporeia) affinis and Pontoporeia femorata, was studied from 12 opensea stations in the northern Baltic Sea between 24 May and 11 June 1993. The M. affinis populations can be geographically grouped according to their physiological condition: (1) eastern Gulf of Finland, with moderate lipid level (mean 24.4% of dry wt) and high V NH4+(45.2 μmol NH4+g-1 dry wt d-1); (2) Bothnian Sea, wigh high lipid level (34.5%) and low V NH4+(24.6 μmol NH4+g-1 dry wt d-1); and (3) Bothnian Bay, with low lipid level (15.2%) and high V NH4+(44.3 μmol NH4+dry wt d-1). A similar pattern could be observed also in the level of triacylglycerols and the neutral-to-polar lipid ratio. P. femorata, the dominating species in the western Gulf of Finland, showed variable “station-specific” excretion rates (22.3 to 43.0 μmol NH4+g-1 dry wt d-1) and lipid levels (23.4 to 30.4%). The spatial variability in the weight-specific V NH4+of M. affinis could not be explained by the differences in the size of individuals, lipid level or lipid class composition; this emphasizes the significance of the effects of spatially differing nutritional conditions, which manifest themselves as different modes of metabolic energy production and different intensities of energy storage. In addition, the potential contribution of the amphipod populations to benthic nitrogen mineralization was estimated; in May to June, the NH4+release of different populations ranged from 12 to 237 μmol NH4+m-2d-1. In general, populations with high abundance and/or biomass release the greatest amounts of NH4+, but the values are modified by the physiological condition of the individuals.

Effects of Pentachlorophenol and Biotic Interactions on Soil Fauna and Decomposition in Humus Soil

In a laboratory experiment, effects of chemical stress (pentachlorophenol, PCP, at concentrations of 0, 50, and 500 mg/kg) and biotic interactions (nematodes in the presence or absence of collembolas and enchytraeids) on the community structure of soil animals and decomposition processes were studied. PCP was strongly adsorbed to humus that contained 65% organic matter. Numbers of fungal-feeding nematodes decreased significantly at the highest PCP concentration, while no effects were found in bacterial feeders. There were differences in the numbers of nematodes between different animal combinations, but at the highest PCP concentration, collembolas and enchytraeids had no effect on them. Numbers of collembola Willemia anophtalma were lowered at the highest PCP concentration, although PCP was not acutely toxic at this concentration. The highest PCP concentration was acutely toxic to enchytraeids, and for an unknown reason all of them died in the main experiment. Both ATP content of the soil and soil respiration were reduced at the highest PCP concentration, while no differences were found between animal treatments. Amounts of NH 4N and PO 4P in the soil increased with increasing PCP concentration. It was concluded that in the presence of simple animal communities, harmful chemicals like PCP regulate the community structure of soil animals as web as decomposition and nutrient mobilization.

Use of ammonium in nutrient solutions

Abstract Three experiments were conducted in greenhouse under hydroponic conditions to study the response of wheat to: i) different ammonium/nitrate (NH4/NO3) ratios, ii) the application of NH4 during different phenological states, and iii) the addition of calcium carbonate (CaCO3) for maximum replacement of NO3 by NH4. Small amounts of NH4 considerably increased yield and grain quality. The best response was observed with a 2/5 ratio NH4/NO3 (meq/L). The application of small fractions of NH4 during grain fill increased production. Dry matter (DM) production decreased when large quantities of NH4 were applied. However, when CaCO3 was used in amounts similar to those of NH4, it was possible to neutralize the acidifing effect of reduced nitrogen (N) and to recuperate DM and grain production, thus increasing the harvest index.

NO reduction in a fluidized bed combustor with primary measures and selective non-catalytic reduction: A screening study using statistical experimental designs

Screening experiments were carried out to study the reduction of NO emissions from a 20 MW circulating fluidized bed (CFB) boiler, equipped with an installation for selective non-catalytic reduction (SNR). The influence of both primary measures and SNR were evaluated, using 2 5−1 and 2 5−2 fractional factorial designs for the two fuels, crushed peat and wood waste, respectively. Polynomial models were deducted from statistical analysis of the experiments, and a good agreement between models and measured data was obtained. The evaluation showed that, by using a designed experimental procedure, CFB operating conditions yielding an NO reduction of 60–80% could be identified, with both primary measures and the SNR being of approximately equal importance. Most important factors for the NO reduction were air:fuel ratio, the amount of NH 3 added, the load and the fraction of lower secondary air; but the reduction is also influenced by small interaction effects. A discussion of the use of experimental designs for increased understanding and optimization of combustion processes is also given.

Application of the ninhydrin-reactive N assay for microbial biomass in acid soils

Values for microbial biomass C and N, as assayed by a fumigation-incubation and a fumigation-extraction method were compared for a range of acid soils. Values for microbial biomass C obtained from CO 2-evolution data using the fumigation-incubation method, were far less than those calculated from ninhydrin-reactive N obtained by the fumigation-extraction method, and in some cases were negative. For a given soil, discrepancies between the two methods of assay increased with soil acidity (pH range, 4–6), and were attributed to an over-correction in the fumigation-incubation assay for CO 2 values of the unfumigated control soil. The extent of overcorrection seemed to be related to the failure of the fumigated, re-inoculated soils to convert organic C to CO 2 at the same rates as in the unfumigated control soils, but not to the amounts per se of readily-decomposable substrate in the soils. By contrast, the amounts of NH 4 + N released during oxidative decomposition of killed microbial cells in the fumigation-incubation method, compared closely with the amounts of NH 4 + N plus amino acid N derived by autolysis and deamination in the fumigation-extraction method. The amounts of nitrogenous products released by the two methods, and hence calculated values for biomass N, were not significantly different. Biomass N (fumigation-incubation) = 1.05 × Biomass N (fumigation-extraction). The performance of the fumigation-extraction assay for biomass C was further evaluated by measuring biomass C in each of the acid soils, as soil pastes in water, and in buffers with pHs ranging between 4–6. The magnitude of the ninhydrin-reactive N flush from chloroform-fumigated soils was increased by soil water content and was affected by soil pH. For soil pastes at 100% water holding capacity, there was a linear relationship between estimated values of biomass C and assay pH. This relationship determined the extent of adjustment of assayed biomass C values to correct for the effects of different soil pHs arising from specific agronomic practices. Biomass C Adjustment Factor = e 0.031(Δ soil pH) Thus, a one unit increase in pH, over the pH range 4–6, gave a 35% increase in the estimated biomass C value. The effects of soil pH and water content on biomass values demonstrates the need for closer standardization of assay indicators, preferably with a wider pH range of soils extending to those of neutral to alkaline pH.

Ammonia production and kinetic properties of glutamate dehydrogenase in the sipinculid Phascolosoma arcuatum exposed to anoxia

The amounts of total NH4+detected in the external media in which Phascolosoma arcuatum had been exposed to various periods of anoxia were significantly greater than those in which the worms were exposed to normoxia for a similar period. The increased NH4+production by P. arcuatum during anoxic exposure was unlikely to be due to an increased catabolism of adenine nucleotides or urea. In contrast, there were significant decreases in the concentrations of several free amino acids in the coelomic plasma and body tissues of individuals during the 48 h of anoxic exposure. The amount of NH4+produced by the anoxic P. arcuatum could be accounted for by the decreases in the concentrations of aspartate or glycine. Increases in the catabolism of free amino acids (FAA), leading to the increased production of NH4+, in P. arcuatum during anoxia were supported by the detection of significant changes in the kinetic properties of glutamate dehydrogenase (GDH), in the deaminating direction, from worms exposed to anoxia for 48 h. The apparent increase in the affinity of GDH from the anoxic worm to glutamate would bring about a greater deaminating activity at physiological concentrations of ths substrate. P. arcuatum used in these experiments were collected from the mangrove swamp at Mandai, Singapore between 1990 and 1993.

Inorganic nitrogen processing and assimilation in a forested wetland

A field study was conducted to assess the capacity of a lower Mississippi Valley, USA forested wetland to process and assimilate inorganic N. Elevated levels of N-15 labeled NH4+ and NO3− -N were added to field plots and emissions of 15N2 and N2O and NH4+- and NO3− -N concentrations in the floodwater were measured over a 67 d study period. Results are given which show the forested wetland soil can remove significant quantities of NH4+ and NO3− from the surface water by assimilation and denitrification processes.