Nitrate Depletion Research Articles

Transformations of nitrogen following epilimnetic N-fertilization in Castle Lake, CA.: 2. Nitrate and ammonium depletion pathways

Transformations of nitrogen following epilimnetic N-fertilization in Castle Lake, CA.: 2. Nitrate and ammonium depletion pathways

Differential Nodulation Tolerance to Nitrate Among Legume Species

Eight legume species were grown in hydroponic culture in controlled environment (CERES phytotron) facilities to determine if the species exhibited differential nodulation tolerance to nitrate nutrition (0, 1.0, and 4.0 mM initial concentrations, allowed to deplete with plant growth). Visible nodule appearance on roots of lupin (Lupinus angustifolius L.), pea (Pisum sativum L.), subterranean clover (Trifolium subterraneum L.), chickpea (Cicer arietinum L.), and siratro [Macropilium atropurpureum (DC:) Urb.] was less sensitive to nitrate than that roots of soybean [Glycine max (L.), Merr.], lablab bean [Lablab purpureus (L.) Sweet], and barrel medic (Medicago truncatula Gaertn.). The latter species also showed marked inhibition of nitrogenase (acetylene reduction) activity with 1.0 mM nitrate treatments, compared with respective 0 mM nitrate controls. The other five species showed similar or higher nitrogenase activity with the 1.0 mM nitrate treatment than with the respective controls. Nitrogenase activity with the 4 mM nitrate treatment was severely (>90%—lupin, chickpea, siratro, soybean, barrel medic, lablab bean), moderately (69%—pea) or slightly (27%—sub clover) inhibited, relative to respective controls. Rates of nitrate depletion from solution and levels of nitrate reductase activity in leaves and roots varied appreciably among species, however no clear relationship was evident that either rate of NO‐3 uptake or site of NO‐3 metabolism was responsible for the differential delays in nodule appearance. Of the species compared, nitrogenase activity of sub clover was least affected by the 4 mM nitrate treatment, and the amount of nitrate remaining in the nutrient solution at the end of the experimental period was greatest for this treatment combination. This indicated that efforts to overcome the inhibitory effect of nitrate on legume nodulation should possibly concentrate on limiting the uptake and/or metabolism of nitrate.

Suppression of nitrate utilization by ammonium and its relationship to chloramphenicol production in Streptomyces venezuelae.

Cultures of Streptomyces venezuelae grown in a medium containing glucose with mixtures of ammonium and nitrate as the nitrogen source produced chloramphenicol in a distinct idiophase that followed biomass accumulation. Analysis of fermentation broths showed that ammonium and nitrate were taken up consecutively by the organism. Measurements of nitrate reductase in the mycelium established that the enzyme was constitutive and that its specific activity did not increase during the period when ammonium was exhausted from the medium and nitrate was assimilated. The enzyme was neither repressed nor inhibited by ammonium. Production of chloramphenicol was also delayed until ammonium had been consumed and remained slow until subsequent depletion of nitrate. Arylamine synthetase, the initial enzyme in the pathway of antibiotic biosynthesis, showed no marked change in specific activity during utilization of the two nitrogen sources. The result suggests that the mechanism causing preferential utilization of ammonium does not simultaneously control the onset of chloramphenicol biosynthesis.

Nitrate reduction and compartmentation in tomato leaves. I. Nitrate accumulation in leaf sections in aqueous and gaseous medium

Nitrate pools in tomato (Lycopersicon esculentum Mill. cv. Azes) leaf sections were estimated. Nitrite accumulation in aqueous medium was found to be an inadequate estimate of nitrate pools in tomato leaves. The main reason for the cessation of nitrite accumulation was not depletion of nitrate in the metabolic pool but rather a rapid decay of nitrate reductase (NR) activity as measured by nitrite accumulation in vivo and in vitro. Nitrate diffuses out of the tissue into the medium at a rate higher than the accumulation of nitrite in the tissue. Nitrate leakage from the tissue accelerates the loss of NR activity. Nitrite accumulation in leaf sections kept in an anaerobic gaseous atmosphere ceased earlier than in aqueous medium, at a time when NR activity was still relatively high. Measuring nitrite accumulation in gaseous atmosphere is preferable since NR is more stable and movements of nitrate between pools more restricted.

Nutrient depletion indicates high primary productivity in the Weddell Sea

The Southern Ocean, and in particular the Weddell Sea, have long been considered areas of high biological productivity1, but recent isotopic measurements of primary productivity have not confirmed this view2,3. Because the large Zooplankton and marine mammal populations of the Southern Ocean depend ultimately on phytoplankton as the base of the food web, accurate knowledge of primary productivity is essential to our understanding of the Antarctic ecosystem. Oceanographie data collected aboard the Soviet icebreaker Mikhail Somov have allowed us to derive a new productivity estimate, based on the seasonal depletion of nitrate, phosphate and silicic acid in the surface layer. From these depletions and data on the elemental composition of Southern Ocean phytoplankton, we estimate average primary productivity in the Weddell Sea in the springtime to be 220–420 mg C m−2 day−1. Our most conservative estimate is 1.5–4 times higher than recently reported measurements of productivity in the open ocean areas of the Southern Ocean2–5. Our estimates are inherently averages over time and space, including the effects of brief, intense spring blooms of phytoplankton which may occur near the receding ice edge6–8. Studies of primary productivity based on isotope uptake experiments, particularly in the austral summer, may fail to account for the significance of such blooms.

Nitrate Deficiency Shortens the Circadian Period in Gonyaulax

The circadian rhythms in bioluminescence and photosynthesis in Gonyaulax polyedra suspended in unsupplemented sea water have been compared to the same rhythms in f/2, an enriched seawater medium. Cells suspended in sea water for 2 days in continuous light (450 microwatts per square centimeter) showed significantly shorter circadian periods and lower amplitudes than did cells in f/2 medium (a period of 22.2 hours as compared to 23.5 hours). Both period and amplitude changes could be completely reversed by the addition of nitrate at one-fourth or more of the concentration in f/2 medium (0.88 millimolar). The addition to autoclaved seawater of phosphate, vitamins, minerals, or soil extract in concentrations present in f/2 medium had no effect. Thus, the shortening of the circadian period is the consequence of reduced nitrogen supply. Since both the rhythms in bioluminescence and photosynthesis showed similarly shortened circadian periods and lower amplitudes, it is probable that the depletion of nitrate directly affects the circadian clock.

Nitrate Depletion in a Second‐Order Mountain Stream

AbstractThe amount of NO3‐N exported in a second‐order mountain stream draining a clearcut and logged mixed hardwood forest was studied over a 4‐year period. Calculations based on measurements of stream chemistry and discharge rates indicated a within‐stream depletion of NO3 from the upper reaches of the stream to the watershed outlet. Within‐stream depletion the first year of treatment was 127% of total NO3‐N discharged from the watershed outlet and declined in succeeding years after treatment to 99, 42, and 5%. Assays of the quantities of denitrifying enzymes in stream sediment samples suggested 1.7 kg N year−1 were lost via this pathway, compared with 3.9 kg N year−1 calculated from within‐stream depletion for the same time period. This study suggests sediment denitrification is a major pathway by which NO3‐N is lost. Within‐stream gaseous transformations are important when accounting for changes in N dynamics associated with forest management practices, and the measurement of only hydrologic discharge of NO3 could result in underestimation of N losses.

Transient situations in nitrate assimilation by marine diatoms. III. short-term uncoupling of nitrate uptake and reduction

The response of nitrate uptake, storage, and reduction by nitrogen-limited cultures of three marine diatoms has been investigated following the addition of nitrate. During perturbation experiments, uncoupling between uptake and reduction was extensive in Skeletonema costatum (Grev.) Cleve and Phaeodactylum tricomutum Bohlin, as internal nitrate could reach 15% of cell nitrogen compared with 1 to 2% under steady-state conditions. This capacity for nitrate storage allowed these species to maintain high rates of nitrate reduction at low external nitrate levels. In contrast, Chaetoceros affinis Lauder accumulated much less nitrate during a perturbation, indicating a closer coupling between uptake and reduction, a phenomenon which was also observed in the field for nitrogen sufficient and nitrogen deficient phytoplankton. Nitrate reduction was related to external nitrate by a hyperbola when data was obtained by either the graded addition or the perturbation method. The relationship to internal nitrate clearly showed saturation kinetics only when data were obtained by the latter method. The sudden decrease in nitrate reduction upon external nitrate depletion, however, made it necessary to separate the data into two groups and to fit them to two hyperbolas with different kinetic characteristics.

Sinking rate response to depletion of nitrate, phosphate and silicate in four marine diatoms

The effect of nutrient (N, P, and Si) depletion on sinking rates was studied for two small (Skeletonema costatum (Grev.) Cleve and Chaetoceros gracile Schutt) and two large [Ditylum brightwellii (West) Grun and Coscinodiscus wailesii (Gran et Angst)] centric diatoms obtained from stock cultures. Each diatom was examined under conditions of (1) nutrient repletion (=log growth phase), (2) nutrient depletion (48 h without a given substrate), and (3) recovery (24h after addition of limiting substrate to nutrient-deplete populations). All nutrient-replete cultures displayed low sinking rates despite large differences in cell size. In nutrient-deplete populations, sinking rate was related to the kind of nutrient depleted and varied among species. Silicate depletion elicited by far the greatest increase in sinking rates in all 4 species, indicating that biochemical aspects of silicon metabolism are more important to buoyancy regulation than density-related variations in the amount of silicon per cell. Since N- and P-depletion caused lower sinking rates in 3 of the species, this observation calls for re-evaluation of the axiom that nutrient depletion necessarily causes increased sinking rates. The exception was Coscinodiscus wailesii, which sank faster under all types of nutrient limitation. In most cases, sinking rates typical of log-phase cultures were not regained within 24 h after the addition of limiting nutrient to nutrient-depleted populations. Ultimately, the length of the recovery period may be useful in identifying the metabolic processes responsible for buoyancy regulation in actively growing cells.

Studies on nitrate uptake by solution grown corn (Zea mays) L. genotypes

Nitrate depletion from the media by intact corn seedlings grown under solution culture was measured over a period of time. Two methods were assessed to differentiate corn genotypes for nitrate uptake ability: (1) Nitrate uptake per day per plant basis. (2) Nitrate uptake per day per gram root dry matter basis. The former method was found to be superior as it gave significant and positive correlations with dry matter, nitrate, and reduced nitrogen accumulation in stem, leaf and roots. Nitrate uptake was found to vary with plant age. Root mass and efficiency of roots appear to contribute to the total nitrate uptake ability of the genotype. Corn genotypes studied exhibited marked differences in nitrate uptake ability.

Differences in Steady-State Net Ammonium and Nitrate Influx by Cold- and Warm-Adapted Barley Varieties

A flowing nutrient culture system permitted relatively rapid determination of the steady-state net nitrogen influx by an intact barley (Hardeum vulgare L. cv Kombar and Olli) plant. Ion-selective electrodes monitored the depletion of ammonium and nitrate from a nutrient solution after a single pass through a root cuvette. Influx at concentrations as low as 4 micromolar was measured. Standard errors for a sample size of three plants were typically less than 10% of the mean.When grown under identical conditions, a variety of barley bred for cold soils had higher nitrogen influx rates at low concentrations and low temperatures than one bred for warm soils, whereas the one bred for warm soils had higher influx rates at high concentrations and high temperatures. Ammonium was more readily absorbed than nitrate by both varieties at all concentrations and temperatures tested. Ammonium and nitrate influx in both varieties were equally inhibited by low temperatures.

Nitrate assimilation and nitrogen circulation in Austrian pine

Nitrate uptake, reduction and translocation were examined in 5‐week‐old Austrian pines (Pinus nigra Arnold var. nigricans Host.) during exposure to 5 mM NaNO3. The rate of nitrate uptake was linear during the 7 h light period. 15N‐NO3− was detected in all parts of the pine except in the needles. By the 7th hour, 43% of the absorbed nitrate had been reduced, and this increased to 64% by the 24th hour. The major part of the total reduction occurred in the roots at this growth stage. Accumulation of 15N in reduced soluble and insoluble fractions was more prevalent in roots than in shoots. In the needles, the translocated nitrogen was mainly incorporated into the insoluble fraction. It is likely that most of the nitrogen from nitrate was transported from the roots to the aerial organs as organic nitrogen; however part of the upward nitrogen flux took place as nitrate ions.An experiment in which an exposure for 24 h to 5 mM Na15NO3 was followed by 13 days exposure to Na14NO3 (pulse chase experiment) revealed a half time of about 1 day for depletion of root nitrate. A large part of this depletion was due to the loss of 15N‐NO3− to the nutrient solution. The remaining pool of 15N‐nitrate was partitioned between a metabolically inactive and an active pool. During the chase period, the simultaneous decrease of 15N‐incorporation in the soluble N fraction and increase in the insoluble N fraction in different pine parts, particularly in the needles, suggested that protein synthesis occurred mostly in young tissues of the shoot and was the major sink of the newly absorbed 15N‐NO3.

Reevaluation of Anaerobic Nitrite Production as an Index for the Measurement of Metabolic Pool of Nitrate

The use of anaerobic nitrite production as an index for the measurement of metabolic pool of nitrate was reevaluated using primary leaves of 7-day-old barley and 10-day-old soybean seedlings. The seedlings were grown in nutrient solutions containing 5 to 15 millimolar nitrate. The nitrate-free in vivo assay system of nitrate reductase was used for measuring the production of nitrite. Both the duration and extent of nitrite production were dependent on the level of endogenous nitrate in the tissue. At cessation of nitrite production, 30 to 50% of the endogenous nitrate was reduced to nitrite. Nitrate from the tissue leaked continuously into the surrounding medium so that, at cessation of nitrite production, nitrate supply from the tissue was exhausted. The cessation of nitrite production, therefore, may have been caused by the depletion of endogenous nitrate from the tissue. It is concluded that anaerobic nitrite production is not a valid index for the measurement of the size of the metabolic pool of nitrate.

The Importance of Regenerated Nitrogen to Phytoplankton Productivity to Phytoplankton Productivity in a Subalpine Lake

Experiments utilizing epilimnetic water were conducted to determine the rate of ammonium regeneration, due to zooplankton excretion and microbial mineralization processes, in relation to the rate of inorganic nitrogen assimilation by phytoplankton. The euphotic zone of dimictic, meso—oligotrophic Castle Lake is characterized by a rapid depletion of both nitrate and ammonium soon after spring thaw. External inputs of nitrogen are minimal during this period and levels of inorganic nitrogen remain low until fall overturn. The rate of ammonium assimilation was high relative to nitrate assimilation, and was significantly correlated with the rate of ammonium regeneration. The importance of this rapid turnover of nitrogen to phytoplankton growth is consistent with the results of previous Castle Lake studies, and with the current conceptual model of primary production in the mixed layer of nitrogen—deficient marine ecosystems.

Upwelling in the Southern Benguela Current

This survey of the southernmost significant upwelling site in the Benguela Current showed that the oceanography is dominated by the seasonal wind cycle of predominant S-E winds in summer and N-W winds in winter. In the upwelling season, extending from September to March, a semi-permanent plume is isolated by a pronounced oceanic front whose position varies in the short-term and is related to wind direction. Surface waters change immediately and deeper waters more slowly to fluctuations in wind. The rate of upwelling was statistically related to wind data. A maximum rate of 32 m day −1 was found. In spring low temperature and salinity water flows northward on the shelf while between late summer and later winter oxygen-depleted water, rich in nutrients, flowed south at an estimated rate of 7–21 × 10 4 m 3 s −1 in a counter current to the Good Hope Jet. Local depletion of oxygen occurs due to phytoplankton decomposition caused, in autumn, by falling light levels and, in summer in calm periods, by nitrate depletion (<1 μg-at N 1 −1). Primary productions is estimated at 3.7 kg C m −2 yr −1 with a maximum growth rate ( PI max) = 17.4–19.0 mg C mg chlorophyll a −1 hr −1 and half-saturation constant ( K S) = 0.4–1.1 μg-at N 1 −1. Nutrients were utilized and oxygen produced: ΔP: ΔN: ΔSi: ΔO=1:19.1 to 23.3:17.5 to 23.3:−227 to −293. High N:Si ratios (maximum 4.28) were found in oxygen-depleted water produced locally while that coming from the north had low ratis, due to resolution of silica from the sediments and nitrate reduction. The mean zooplankton standing stock, 2.3 g dry weight m −2, was 12% of the phytoplankton crop. In summer stocks were maximal 40–100 km and minimal 20–50 km from the coast while in winter they were maximal inshore. Little vertical migration occurred and the waters above the thermocline contained the majority of the population.

Nitrate Uptake Effectiveness and Utilization Efficiency of Two Plum Clones

AbstractNitrate uptake and utilization efficiencies of two plum clones, Marianna 2624 (Prunus cerasifera×Prunus munsoniana?) and Myrobalan 3‐J (Prunus cerasifera) in stirred solution cultures were investigated. Myrobalan 3‐J had a significantly lower NO3‐ compensation point (i.e., greater capacity for nitrate depletion) but ceased growth earlier than Marianna 2624 under severe N stress. The maximum velocity of NO3‐ uptake was 33% higher in Marianna 2624 than Myrobalan 3‐J. The nitrogen efficiency ratio (i.e., mg dry weight produced/mg nitrogen absorbed) of Marianna 2624 was 40% higher than Myrobalan 3‐J when nitrogen was severely limiting (28 mg nitrogen per plant). Thus, Marianna 2624 plants may be capable of growth at lower mean nitrogen concentrations.

Phytoplankton Ecology of the Strait of Georgia, British Columbia

Observations of phytoplankton production, abundance, and distribution were made at 16 stations in the Strait of Georgia from 1975 to 1977. The discharge of turbid Fraser River water exerts a strong influence on phytoplankton production and distribution in surface waters by rapid light attenuation and horizontal advection. At plume boundaries and back eddies where light conditions improve, very high production occurs (&gt; 4–5 g C∙m−2∙d−1), because of rapidly replenished nutrients supplied by the Fraser River. Advection, turbulence, zooplankton grazing, and summer nitrate depletion collectively impart a heterogeneous distribution pattern to phytoplankton in the surface waters of the Strait of Georgia. Mean annual production varies from lows of 150 g C∙m−2 in Fraser River plume to highs of over 500 g C∙m−2 in sheltered boundary waters of inlets. Recent increases in ammonia and nitrate from land drainage and domestic sewage, mainly through the Fraser River, are related to increases in phytoplankton standing stocks in the Strait. Key words: phytoplankton, primary production, eutrophication, coastal marine, phytoplankton distribution and succession, chlorophyll a, pelagic

Blooms of surf-zone diatoms along the coast of the Olympic Peninsula, Washington: IX. Factors controlling the seasonal cycle of nitrate in the surf at Copalis Beach (1971 through 1975)

Nitrate depletion in the upper water layers beyond the breaker zone at Copalis Beach, Washington, takes place in April of each year due to spring phytoplankton blooms. In 1974, Thalassiosira pacifica was the species responsible for almost all of the nitrate depletion over a considerable ocean area beyond the region of the breakers. This same nitrate-depleted water was also characteristic of the surf zone in April of each year (1971 through 1975). Between mid-April and mid-October, reintroduction of nitrate into the surf region depends on encroachment of upwelled oceanic deep water high in nitrate; in 1971, when there was only weak upwelling, nitrate in the surf remained depleted over an extended period (6 months). Upwelling can be masked by the presence of freshwater discharge from rivers and streams (as in 1971, 1972 and 1974). In the summer of 1973, when the rate of river discharge was at an all-time record low, nitrate concentrations in surf samples were higher than in any of the other summers during our study period. Cell concentrations of both surf diatom species were reduced in summer; Asterionella socialis disappeared completely in mid or late summer, and Chaetoceros armatum showed symptoms of physiological stress. The annual cycles of abundance of each species seemed to be repeated in more or less the same fashion from year to year, in spite of the very different patterns observed in nitrate concentrations from summer to summer. This points to the importance of ammonia as an alternate nitrogen source for surf diatoms, particularly during summer months.

THE FATE OF SODIUM NITRITE IN BACON

ABSTRACTUsing 1 5 N‐labelled sodium nitrite cured pork bellies, with and without the addition of sodium ascorbate, we have attempted to trace the reaction pathways of nitrite in bacon. The depletion of nitrite, originahy at 156 ppm, was followed during the processing operation. Subsequent experiments during the storage of the 1 5 N labelled, sliced, vacuum packaged bacon showed the further depletion of nitrite in both the lean and adipose tissue portions, the lower nitrite levels being found in the bacon to which ascorbate had been added. The formation and depletion of nitrate was also noted. Analysis of the protein and lipid portions showed incorporation of 1 5 N into both. Mass spectral measurements showed that between 73 and 87% of the added 1 5 N remained in the bacon lean portion. The adipose portion contained much less 1 5 N, equivalent to between 20–25% of that added. A hot water extract of both lean and adipose fractions showed the presence of 1 5 N greater than the 1 5 N due to nitrite and nitrate. One effect of the addition of ascorbate was to force 1 5 N into water soluble compounds. Examination of connective tissue protein isolated from the adipose tissue portion showed incorporation of 1 5 N equivalent to 6 ppm NaNO2 in bacon without ascorbate compared to 2.5 ppm for bacon with added ascorbate. 1 5 N data also showed incorporation of approximately 25% of the added nitrite into the muscle proteins of both bacons, and incorporation of 10% of the added nitrite into the lipid fraction of the adipose tissue.

Significance of cellular nitrate content in natural populations of marine phytoplankton growing in shipboard cultures

Phytoplankton intracellular nitrate concentrations have been monitored in a 56-h experiment on a shipboard culture of surface sea water from an upwelling region. These measurements were related to parameters of biomass (particulate nitrogen) and nitrate assimilation using the 15N isotope technique and the nitrate reducase (NR) assay. The procedure for measuring cellular nitrate concentrations is described. This parameter exhibited diurnal variations, ranging from 3.1 to 20.6 ng-at nitrate per μg-at particulate nitrogen, and could be correlated positively with NR activity. Nitrogen budgets show that NR activity represents only 12% of nitrate incorporation in organic phytoplankton material when nitrate is available in the sea water. However, upon depletion of the environmental nitrate (zero uptake), NR activity can fully account for the decrease of internal nitrate. From the results, it seems that internal nitrate content is a better index of nitrate consumption by marine phytoplankton than the external concentration of nitrate-nitrogen.