Changes In Ammonium Concentrations Research Articles

A developed system to extract specific responses of increment length in rice shoots under gradient changes in nitrogen concentration regimes.

Nitrogen (N) fertilization is one of the most crucial factors that contribute to increasing food production requiring the generation of rice cultivars with improved N use efficiency (NUE) to maintain yield during low N fertilizer application. To assay NUE extent, we developed a screening system to evaluate shoot growth of each rice cultivar under gradient changes in N concentrations. This system comprises a gradient hydroponic culture and growth visualization systems. The former allows gradient changes in ammonium concentrations, while the latter records the increment in shoot length of individual rice seedlings at given time periods using a fixed-point camera. We chose 69 cultivars including two controls (Oryza sativa L. cv. Nipponbare [WRC01] and Kasalath [WRC02]) from the World Rice Core Collection to investigate shoot growth responses under ammonium-sufficient, ammonium-limited, and low ammonium concentration gradients without transplanting stress. We observed three growth patterns in response to different ammonium concentrations. Subsequently, we selected three representative cultivars (Kasalath, WRC03, and WRC05) for the characteristic responses under the different ammonium environments. Distinct expression patterns of glutamine synthetase 1;2 (OsGS1;2) but OsGS1;1 were observed in response to varying ammonium concentration regimes, indicating that the expression patterns of OsGS1;2 may be a growth marker in terms of shoot growth when transitioning from ammonium-limited to low ammonium concentrations. This system with the level of OsGS1;2 allows us to screen for candidate cultivars that return high NUE in low N environments.

Changes in Ammonium and pH within Intertidal Sediments in Relation to Temperature and the Occurrence of Non-Indigenous Bivalves

Our objective was to determine the role of two invasive bivalves on the concentration of ammonium as well as pH within intertidal surface sediments (0 - 3 and 3 - 6 cm depth) and interstitial waters, within the context of a warming environment. To meet this objective we applied both controlled laboratory (microcosm) and field (mesocosm) experiments where we varied bivalve presence and absence and sediment temperature. Mesocosm sampling was tide dependent as we attempted to capture changes in ammonium concentration and pH as related to flood and ebb tide. We focused on ammonium as this nutrient is typically a limiting nutrient in oceanic systems and its cycling is a key process that regulates biological productivity. We also determined pH because of the increasing threat of ocean acidification. Integration of laboratory and field studies suggests that bivalves significantly contribute to ammonium to the intertidal with this amount increasing with increasing temperature. This ammonium is then released from the sediment as a “pulse” to overlying seawater on the flood tide. Under laboratory conditions, increased temperature and density of bivalves decreased overlying water pH. Mesocosm studies suggested some tide dependence of pH with flood tide acting as a buffer, increasing pH on the flood tide, after sediment exposure during ebb tide. Increased numbers of invasive bivalves within a warming environment are likely to increase amounts of ammonium released as a pulse on flood tides from intertidal ecosystems making this region a source of ammonium to coastal seas. Greater numbers of non-indigenous bivalves within the intertidal could also contribute to increased acidity within these regions although the significance of such increases is unknown.

Modeling historical long‐term trends of sulfate, ammonium, and elemental carbon over Europe: A comparison with ice core records in the Alps

The regional EMEP chemical transport model has been run for the 1920–2003 period and the simulations compared to the long‐term seasonally resolved trends of major inorganic aerosols (sulfate and ammonium) derived from ice cores extracted at Col du Dôme (CDD, 4250 m above sea level, French Alps). Source‐receptor calculations have been performed in order to allocate the sources of air pollution arriving over the Alps. Spain, Italy, France, and Germany are found to be the main contributors at CDD in summer, accounting for 50% of sulfate and 75% of ammonium. In winter more European wide and trans‐Atlantic contributions are found. The relative impact of these sources remains similar over the whole Alpine massif although transport from US and emissions from Spain contribute less as we move eastward from CDD, toward other alpine ice core drill sites like Colle Gnifetti (CG) in the Swiss Alps. For sulfate, the CDD ice core records and the simulated trends match very well. For ammonium, the trend simulated by the model and the summer ice core record are in reasonable agreement, both showing greater changes in ammonium concentrations than would be suggested by historical ammonia emissions. Motivated by a such good agreement between simulations of past atmospheric concentrations and ice core records for inorganic aerosol species, we also use the model to simulate trends in elemental carbon for which less information on past emission inventories are available.

Effects of management regime and plant species on the enzyme activity and genetic structure of N‐fixing, denitrifying and nitrifying bacterial communities in grassland soils

Management by combined grazing and mowing events is commonly used in grasslands, which influences the activity and composition of soil bacterial communities. Whether observed effects are mediated by management-induced disturbances, or indirectly by changes in the identity of major plant species, is still unknown. To address this issue, we quantified substrate-induced respiration (SIR), and the nitrification, denitrification and free-living N(2)-fixation enzyme activities below grass tufts of three major plant species (Holcus lanatus, Arrhenatherum elatius and Dactylis glomerata) in extensively or intensively managed grasslands. The genetic structures of eubacterial, ammonia oxidizing, nitrate reducing, and free-living N(2)-fixing communities were also characterized by ribosomal intergenic spacer analysis, and denaturing gradient gel electrophoresis (DGGE) or restriction fragment length polymorphism (RFLP) targeting group-specific genes. SIR was not influenced by management and plant species, whereas denitrification enzyme activity was influenced only by plant species, and management-plant species interactions were observed for fixation and nitrification enzyme activities. Changes in nitrification enzyme activity were likely largely explained by the observed changes in ammonium concentration, whereas N availability was not a major factor explaining changes in denitrification and fixation enzyme activities. The structures of eubacterial and free-living N(2)-fixing communities were essentially controlled by management, whereas the diversity of nitrate reducers and ammonia oxidizers depended on both management and plant species. For each functional group, changes in enzyme activity were not correlated or were weakly correlated to overall changes in genetic structure, but around 60% of activity variance was correlated to changes in five RFLP or DGGE bands. Although our conclusions should be tested for other ecosystems and seasons, these results show that predicting microbial changes induced by management in grasslands requires consideration of management-plant species interactions.

Nitrogen in rainfall, cloud water, throughfall, stemflow, stream water and groundwater for the Plynlimon catchments of mid-Wales

An extensive study of acidic and acid sensitive moorland and forested catchments in mid-Wales is used to show the water quality functioning with respect to nitrate and ammonium. For this, long-term records of rainfall, cloud water, throughfall, stemflow and stream water (up to 18 years of weekly data) are combined with shorter duration information on stream water associated with small tributary sources and drainage ditches, ground water from a network of exploratory boreholes and paired control and felled catchments. The ratio of nitrate to ammonium is about one in rainfall, cloud water, throughfall and stemflow but the concentrations are much lower in rainfall (∼25 μM l −1) than in cloud water (∼300 μM l −1) while throughfall and stemflow are intermediate (∼80 μM l −1). Within the streams draining moorland and forested areas, nitrate concentrations are close to the mean value in rainfall while ammonium concentrations are often over an order of magnitude lower in the stream than in rainfall and are typically only about a fifth that of nitrate. With felling, stream water nitrate concentrations increase for podzolic soils but show a variable response for gley soils. For the streams draining forested podzols, the concentrations of nitrate can be up to an order of magnitude higher for the first few years after felling compared to than pre-fell values but in later years, concentrations decline to pre-fell and even lower levels. Felling for the podzolic soils barely leads to any changes in ammonium concentration. For the gley soils, felling results in an order of magnitude increase in nitrate and ammonium for a small drainage ditch, but the pulse barely reaches the main stream channel. Rather, within-catchment and within-stream processes not only take up the nitrate and ammonium fluxes generated, but in the case of nitrate, concentrations with- and post-felling are lower than pre-felling concentrations. Groundwater concentrations of nitrate for the moorland and forested catchments are slightly lower than for the streams while for ammonium the reverse is the case: ammonium concentrations in groundwater are about a tenth those of nitrate. With felling, groundwater nitrate concentrations show sporadic increases. For two boreholes, these increases occur during wet periods when groundwater levels are at their shallowest; for one other borehole, there is a gradual and sustained increase over several years. The results are explained in relation to the dominant hydrogeochemical processes operative.

Determination of ammonium in milk and dairy products by ion chromatography

To control the quality and the biochemical evolution of milk and dairy products during their technological transformations, it is interesting to determine their ammonium concentrations. A chromatographic method for the determination of this compound is proposed. The method is based on the separation of ammonium by cation-exchange chromatography and its detection by suppressed conductivity. With an appropriate sample preparation, this method enabled identification and quantification of ammonium with good repeatability (relative standard deviation of about 5%). Moreover, good sensitivity (less than 0.5 mg/kg) and no interference between ammonium and other matrix components were determined. It was also shown that this method offers a very promising alternative for studying changes in ammonium concentration of milk or caseinate after their heat treatments and in different dairy products such as yoghurt and cheeses (hard cooked and mould ripened cheeses).

Adaptation ofRhodococcus rhodochrous M8, a producer of acrylamide, to changes in ammonium concentration in the growth medium

The mechanism of adaptation of the acrylamide producing strainRhodococcus rhodochrous M8 to changes in ammonium concentrations in the medium was studied. An increase in the content of ammonium in the medium changed the activity of glutamine synthetase (GS) (EC 6.3.1.2) and glutamine dehydrogenase (GD) (EC 1.4.1.4), the enzymes of ammonium assimilation, as well as the activities of enzymes responsible for nitrile utilization: nitrile hydratase (EC 4.2.1.84) and amidase (EC 3.5.1.4). This also inhibited the activation of GS induced by phosphodiesterase (EC 3.1.4.1 ). Increases in the activities of nitrile hydratase and amidase and resistance of these enzymes to ammonium were observed in mutant ofR. rhodichrous resistant to phosphotricine, an inhibitor of GS. An important role of GS in the mechanism of adaptation is suggested.

Influence of field-based nutrient enrichment on the photobiology of the giant clam Tridacna maxima

Nutrients were added to 12 microatolls in One Tree Island lagoon every low tide for 13 mo to an initial concentration of 10 mu M (ammonium, N) and 2 mu M (phosphate, P). These concentrations remained above background for 2 to 3 h after addition. The addition of ammonium (N and NI-P but not P alone) significantly increased P, (gross photosynthesis) P,, (net photosynthesis) and R (respiration) per unit wet-tissue weight and cc (photosynthetic efficiency) in Tridacna maxima after 3 mo nutrient enrichment. These responses to small and transient changes in ammonium concentrations suggest that symbiotic clams are not nutrient-replete, and that even subtle changes in nutrients can have a measurable effect on photosynthesis. The same clams did not show significant differences in photosynthetic parameters 6 mo after the beginning of nutrient enrichment, suggesting that their previous responses had either been seasonal or that symbiotic clams such as T. maxima are able to adjust their photophysiology following external changes in nutrient concentrations.

Modelling simultaneous release, diffusion and nitrification of ammonium in the soil surrounding a granule or nest containing ammonium fertilizer

A model of nitrogen release from ammoniacal fertilizers into soil (e.g. from a controlled release nitrogen (CRN) source) and subsequent nitrification has been developed to assess possibilities for reducing losses of N and environment pollution. Emphasis was placed on the effects of changes in ammonium concentration and pH on nitrification rates, and the interactions of these effects with the rate of release of N from fertilizers. The model considers ammonium release and transport from a spherical source, such as a coated granule of CRN or a nest containing either granules of CRN or an easily dissolved fertilizer (EDF). It is shown that the appearance of nitrate in the soil decreases as the size of the N source increases. This is due to both a decrease in the rate of nitrification, caused by accumulation of ammonium near the source, and a slower relative release (i.e. smaller ratio of N released per unit time to the total mass initially in the source, which is inversely proportional to the radius of a granule or nest). Placement of many CRN granules in a nest is shown to be an effective way to reduce nitrification, particularly in soils having low microbial activities. The less the mobility of ammonium in the soil, the slower will be the nitrification because ammonium accumulates close to the source. A CRN nest leads to more effective reduction of nitrification than an EDF nest and N in it is released more slowly into the soil.

Diurnal changes in near-surface ammonium concentration—interplay between zooplankton and phytoplankton

Data from a cruise in 1996 in the Southern Ocean near the island of South Georgia indi- cate that ammonium concentrations in near-surface waters (top 30 m of the water column) varied diumally by -0.2-035 mmol m-1 day1 (3 h mean values) in different regimes. Maximum values (up to 1.3 mmol nr3) occurred around local midnight and minimum values (down to 0.1 mmol m--1) close to noon. This cyclicity was not found in other nutrients analysed (silicate, nitrate, nitrite and phos- phate). The potential for muting ammonium-rich water from the pycnocline into the surface mixed layer (SML) at night is examined. Budget calculations for both ammonium and temperature suggest that complete mixing of the pycnocline water into the SML would increase concentration to observed levels. However, it would also give rise to changes in pycnocline ammonium concentration and tem- peratures which do not agree with observations. Moreover, such a model will not account for daytime drawdown, which is likely to be due to biological processes. A simple biological model combining night-time excretion of ammonium by zooplankton and daytime uptake by phytoplankton simulates the observed change, but only if (i) the daily-averaged phytoplankton gTowth rate was of the order of 0.5-1 day-', (ii) this growth was strongly dependent on ammonium for its nitrogen nutrition, (iii) zooplankton grazing was sufficient to keep phytoplankton biomass at a constant level and (iv) much of the ingested nitrogen was excreted. The implications of these conditions are explored in the context of other observations during the study, and on the basis of published data. It appears that the re- supply of inorganic nitrogen through zooplankton grazing may have been important in sustaining primary production, indicating a very tight coupling between grazers and their food supply. This con- clusion is supported by comparison with results from a similar cruise in 1994. Then there was a reduc- tion in the biomass of Antarctic krill, a major component of the zooplankton, to 14% of that observed in 1996. Diurnal change in ammonium concentration could not be detected and phytoplankton growth rate had been slower (about 0.25 d~'), providing support for the suggestion that biological processes were more important than physical mixing in generating ammonium cyclicity. The potential conse- quences for the biological cycling of carbon in high- and low-krill abundance years are discussed.

Nitrification: A Significant Cause of Oxygen Depletion Under Winter Ice

Changes in concentrations of ammonium, nitrite, nitrate, and oxygen suggested the occurrence of significant nitrification throughout the water column of mesotrophic Lake St. George, Ontario, during the winter months from 1976 to 1984. The existence of nitrapyrin- and acetylene-sensitive 14C-bicarbonate incorporation confirmed that bacterial nitrification occurred. During late January to early March (water temperature 2–3 °C), nitrification occurred at an average rate of about 13 μg N∙L−1∙d−1 for the years studied. Numbers of detectable nitrifying bacteria appeared too low (by 2 to 4 orders of magnitude) to account for the observed activity. The nitrification activity observed would result in average oxygen consumption amounting to 71% of the observed oxygen depletion. This shows that winter nitrification can be an important factor in promoting oxygen depletion and possibly winter-kill of fish.

The location and persistence of ammonia (aqueous, anhydrous and anhydrous + ‘N-serve’) injected into a sandy loam soil, as shown by changes in concentrations of ammonium and nitrate ions

SUMMARYAqueous and anhydrous ammonia were injected into a sandy loam soil, using equipment fitted with commercial injector knives. Ammonium and nitrate concentrations around the injection slits were sampled at intervals in three experiments, from March to November, December to September, and June to December.The depth of placement and pattern of distribution of ammonium nitrogen resulting from the two designs of injector knife employed were measured.The rate of disappearance of ammonium nitrogen was followed, and the process described by a computer program which took account of soil temperature. The rate of decay of both aqueous and anhydrous ammonia could be described approximately by assuming a decay rate of 1% per day at 0 °C and Q10of 2·1. When 1·5% ‘N-serve’ was added to anhydrous ammonia the rate of decay was approximately halved.The distribution pattern of nitrate ions in the soil was less well defined than that of ammonium ions. When ‘N-serve’ had been added to anhydrous ammonia nitrate concentrations were much depressed for the whole duration of the experiment. The conversion of ammonium to nitrate nitrogen in this soil appeared to be inefficient. The nitrate concentrations found in the soil were consistent with a conversion rate of one-third and with the predictions made by a leaching model using the local meteorological data.The implications of the findings are discussed.