15N Tracer Method Research Articles

Soil nitrogen transformations under Populus tremuloides, Betula papyrifera and Acer saccharum following 3 years exposure to elevated CO2 and O3

AbstractIncreases in atmospheric CO2 and tropospheric O3 may affect forest N cycling by altering plant litter production and the availability of substrates for microbial metabolism. Three years following the establishment of our free‐air CO2–O3 enrichment experiment, plant growth has been stimulated by elevated CO2 resulting in greater substrate input to soil; elevated O3 has counteracted this effect. We hypothesized that rates of soil N cycling would be enhanced by greater plant productivity under elevated CO2, and that CO2 effects would be dampened by O3. We found that elevated CO2 did not alter gross N transformation rates. Elevated O3 significantly reduced gross N mineralization and microbial biomass N, and effects were consistent among species. We also observed significant interactions between CO2 and O3: (i) gross N mineralization was greater under elevated CO2 (1.0 mg N kg−1 day−1) than in the presence of both CO2 and O3 (0.5 mg N kg−1 day−1) and (ii) gross NH4+ immobilization was also greater under elevated CO2 (0.8 mg N kg−1 day−1) than under CO2 plus O3 (0.4 mg N kg−1 day−1). We used a laboratory 15N tracer method to quantify transfer of inorganic N to organic pools. Elevated CO2 led to greater recovery of NH4+‐15N in microbial biomass and corresponding lower recovery in the extractable NO3− pool. Elevated CO2 resulted in a substantial increase in NO3−‐15N recovery in soil organic matter. We observed no O3 main effect and no CO2 by O3 interaction effect on 15N recovery in any soil pool. All of the above responses were most pronounced beneath Betula papyrifera and Populus tremuloides, which have grown more rapidly than Acer saccharum. Although elevated CO2 has increased plant productivity, the resulting increase in plant litter production has yet to overcome the influence of the pre‐existing pool of soil organic matter on soil microbial activity and rates of N cycling. Ozone reduces plant litter inputs and also appears to affect the composition of plant litter in a way that reduces microbial biomass and activity.

Evaluation of Nitrogen Removal Potential in a Reed Filter Bed System by the 15N Tracer Method

The mechanisms of nutrient removal in a sand-filled reed filter bed (RFB) system involve filtration, sedimentation, plant uptake and microbial degradation in the soil-water interface and plant rhizosphere where the nitrification-denitrification process occurs. Information concerning these mechanisms, however, is limited, especially regarding the denitrification rate in a RFB system. With this in mind, the denitrification rates were directly measured using the 15N tracer method. In addition, the seasonal changes of the denitrification rates were investigated. Using a bench-scale RFB system and sand filter system without reeds, denitrification rates ranging from 0.0 to 5.5 (average 2.27) and 0.0 to 3.4 (average 1.48) g-N m2 d, respectively, were obtained. These values indicate that about 60 and 80% of inflow nitrogen loading was removed by denitrification. It was also found that 25% of inflow nitrogen loading in the RFB system was removed by plant uptake. The higher denitrification rate in the RFB system suggested that the microbial activity in the reed rhizosphere is of key importance for the nitrogen removal efficiency during the stationary phase of the reed's growth curve. As for their associated seasonal changes, the denitrification rates were proportional to air temperature, so that the denitrification rates were lowest during the winter. Although the denitrification rate in the RFB system was only 0.23 to 0.68 g-N/m2 d at 6.2 to 11.2 °C in December 1998, the increase of air temperature to 26.2 °C using a temperature-controlled room remarkably enhanced the denitrification rate to 2.95 g-N/m2 d. This result confirmed the possibility that the RFB system could maintain denitrification activity by controlling air temperature.

Release of dissolved organic nitrogen from Scenedesmus quadricauda (Chlorophyta) and Microcystis novacekii (Cyanobacteria)

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 27:275-284 (2002) - doi:10.3354/ame027275 Release of dissolved organic nitrogen from Scenedesmus quadricauda (Chlorophyta) and Microcystis novacekii (Cyanobacteria) Fumitaka Nagao1, Tatsuo Miyazaki2,* 1Laboratory of Marine Environmental Microbiology, Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan 2Marine Biosystems Research Center, Chiba University, Amatsu-Kominato, Awa-gun, Chiba-ken 299-5502, Japan *Corresponding author. E-mail: myzkt@beige.ocn.ne.jp ABSTRACT: We measured the time-course of dissolved organic nitrogen (DON) release and inorganic nitrogen assimilation in the freshwater phytoplankton Scenedesmus quadricauda (Turp.) Brébission and Microcystis novacekii (Kom.) Comp. by the 15N tracer method. The algae were cultivated under nitrogen-limited or -replete conditions. We estimated the total DON release, release of recently assimilated nitrogen (RANR) and net nitrogen assimilation (NNA), using ammonium chloride or sodium nitrate as the nitrogen source. In the 15N tracer incubation of S. quadricauda prior to 1 h and in M. novacekii prior to 3-6 h, minimal release of total DON was observed under the nitrogen-limited conditions. This result suggests that nitrogen-limited cells efficiently use incorporated nitrogen. Appreciable release of total DON was observed in the 15N incubation of nitrogen-replete S. quadricauda and M. novacekii. RANR in both nitrogen-limited and -replete algae was smaller than, and lagged behind, release of total DON, indicating that newly assimilated nitrogen was less easily released. NNA by nitrogen-limited S. quadricauda increased from the onset of the tracer incubation, showing that ambient nitrogen was needed for nitrogen-limited cells from the beginning of the incubation. Nitrogen-replete S. quadricauda showed no NNA during the first 1 h of the tracer incubation, suggesting that the alga did not require external nitrogen immediately after being transferred from nitrogen-replete conditions. This study shows that nitrogen release and assimilation are markedly affected by the nutritional states of the algae. KEY WORDS: Ammonium · Nitrogen assimilation · Organic nitrogen release · Microcystis novacekii · Nitrate · Scenedesmus quadricauda Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 27, No. 3. Online publication date: April 16, 2002 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2002 Inter-Research.

Nitrous oxide production in high-loading biological nitrogen removal process under low cod/n ratio condition

Effects of influent COD/N ratio on N 2O emission from a biological nitrogen removal process with intermittent aeration, supplied with high-strength wastewater, were investigated with laboratory-scale bioreactors. Furthermore, the mechanism of N 2O production in the bioreactor supplied with low COD/N ratio wastewater was studied using 15N tracer method, measuring of reduction rates in denitrification pathway, and conducting batch experiments under denitrifying condition. In steady-state operation, 20–30% of influent nitrogen was emitted as N 2O in the bioreactors with influent COD/N ratio less than 3.5. A 15N tracer study showed that this N 2O originated from denitrification in anoxic phase. However, N 2O reduction capacity of denitrifiers was always larger than NO 3 −–N or NO 2 −–N reduction capacity. It was suggested that a high N 2O emission rate under low COD/N ratio operations was mainly due to endogenous denitrification with NO 2 −–N in the later part of anoxic phase. This NO 2 −–N build-up was attributed to the difference between NO 3 −–N and NO 2 −–N reduction capacities, which was the feature observed only in low COD/N ratio operations.

Comparison between chemical and isotopic measurements of biological nitrate utilization: further evidence of low new-production levels in the equatorial Pacific

New-production (nitrate uptake) rates in the equatorial Pacific were estimated by parallel measurements of nitrate disappearance from sea water using a colorimetric method and of 15N-labelled nitrate (15NO3 −) incorporation into particulate organic nitrogen (PON) collected on GF/F filters (net nitrate uptake, conventional 15N-tracer method) and Anopore (0.2 μm) membranes. Regression analyses of 74 sample pairs gathered during 12 and 24 h productivity experiments revealed a significant positive relationship between decreasing nitrate level and 15NO3 − accumulation into PON retained on GF/F filters, but the slopes of Model I and Model II regression lines were 1.18 and 1.29, respectively, suggesting that 15 to 22% of 15NO3 − removed from the dissolved fraction were lost to another N-pool. Two possible avenues for the missing 15NO3 − have been examined: uptake by submicron particles passed through the GF/F filters, and loss as dissolved organic nitrogen (DON). Nitrate uptake by small cells not recovered on GF/F filters, could be safely eliminated as a cause of loss, since 15NO3 − uptake rates obtained from 15N entering PON collected on GF/F filters agreed well with those obtained from 15N entering PON collected on Anopore membranes (32 sample pairs). Inspection of the DON pool of 0.2 μm filtrates for excess-15N enrichment (20 samples) revealed that in nitrate-rich waters (equatorial upwelling between 1°N and 10°S), loss of 15NO3 − as DO15N accounted for 2) were probably erroneous; (2) the use of GF/F filters does not result in an underestimation of new production, although it was found to underestimate PON concentrations by up to 60%; (3) in the equatorial upwelling area (1°N to 10°S), which has high ambient nitrate levels (>2000 nmol l−1) but only slight changes in concentration (0 to 80 nmol l−1 d−1), new production is more accurately estimated by the isotopic method than by the chemical method; (4) in subtropical oligotrophic waters (from 11°S southward) with low ambient nitrate levels (0 to 100 nmol l−1), both procedures are appropriate as long as nitrate removal per incubation period is >3 nmol l−1 (lower rates are only detectable with the isotopic method); (5) the traditional 15N-tracer technique does not substantially underestimate net new-production in the equatorial Pacific, and failure to account for the loss of 15NO3 − as DON, i.e. to estimate gross nitrate uptake (gross uptake = net uptake + 15N loss) tends to underestimate new production on an average by only 10%. Overall, the apparent low level of new production in the nitrate-rich area of the central equatorial Pacific seems to be a fact, and may be ascribable to other nutrient (macro and micro) deficiencies and/or to intense in situ recycling of ammonium and nitrate (regenerated production) rather than to inaccurate nitrate uptake rates measured with the classical 15N-tracer technique.

｀１５´Ｎトレーサー法を用いたヨシフィルターの窒素除去性能に関する研究

The mechanisms of nutrient removal in sand-filled reed filter bed system (RFB system) are explained by filtration, sedimentation, plant uptake and microbial degradation occurring in soil-water interface and in the plant rhizosphere, which includes nitrification-denitrification process. There is, however, little information on it, especially information on denitrificaton rate in RFB system has not been obtained. The objective of this study is to measure denitrification rates using 15N tracer method and investigate seasonal changes of them throughout a year. The results of bench-scale RFB system using 15N tracer method showed that the denitrification rates of the RFB and the sand tank without reeds ranged from 0.0∼5.5 (average 2.28) and 0.0∼3.4 (average 1.48) g-N · m-2 · d-1, respectively. These values mean that about 60% in the RFB and about 80% in the sand tank for inflow nitrogen loading were removed by denitrification. A part of remaining nitrogen loss in nitrogen balance of the RFB tank might be caused by plant uptake. High denitrification rate in the RFB suggested that microbial activity in the reed rhizosphere played an important role in nitrogen removal efficiency during the stationary phase of reed's growth curve.

A modified 15N tracer method and new calculation for estimating release of dissolved organic nitrogen by freshwater planktonic algae

A modified 15N tracer method and new calculation for estimating release of dissolved organic nitrogen by freshwater planktonic algae

Application of a 15N tracer method to the study of dissolved organic nitrogen uptake during spring and summer in Chesapeake Bay

The dissolved organic nitrogen (DON) pool in marine waters contains a diverse mixture of compounds. It is therefore difficult to accurately estimate planktonic uptake of DON using the limited number of radiolabeled compounds commercially available. We describe a method to estimate DON uptake rates using 15N-labeled DON recently released from phytoplankton. To make 15N-labeled DON, we incubated surface water with 15NH 4 + and then isolated the DON, including any recently released DO15N, with ion retardation resin. This DON was then added to a freshly collected water sample from the same environment to quantify the rate of DON uptake. The technique was applied to investigate rates of DON uptake relative to inorganic nitrogen in the mesohaline Chesapeake Bay during May 1990 and August 1991. The May experiment took place after the spring bloom, and rates of DON uptake [ranging from 0.31 to 0.53 μg-atom (μg-at) Nl-1 h-1] often exceeded rates of NH 4 + and NO 3 - uptake combined. The rates of DON uptake at this time were higher than estimated bacterial productivity and were not correlated with bacterial abundance or bacterial productivity. They were, however, correlated with rates of NO 3 - uptake. In May, we estimate that only 7 to 32% of DON uptake was a result of urea utilization. In contrast, in August, when regenerated nutrients predominate in Chesapeake Bay, rates of DON uptake (ranging from 0.14 to 0.51 μg-atom Nl-1 h-1) were an average of 50% of the observed rates of NH 4 + uptake. Consistent with the May experiment, rates of DON uptake were not correlated with bacterial production. A sizable fraction of DON uptake, however, appeared to be due to urea utilization; rates of urea uptake, measured independently, were equivalent to an average of 74% of the measured rates of DON uptake. These findings suggest that, during both periods of study, at least a fraction of the measured DON uptake may have been due to utilization by phytoplankton.

The western North Atlantic bloom experiment

An investigation of the spring bloom was carried out in the western North Atlantic (40–50°W) as one component of the multi-nation Joint Global Ocean Flux Study (JGOFS) North Atlantic Bloom Experiment (NABE). The cruise track included an extended hydrographic section from 32 to 47°N and process studies at two week-long time-series stations at 40 and 45°N. Biological and chemical data collected along the transect indicated that the time-series stations were located in regions where the spring bloom was well developed; algal biomass was high and surface nutrient concentrations were reduced from maximum wintertime levels. Despite similarities in the vertical structure and magnitude of phytoplankton biomass and productivity, the two stations clearly differed in physical, chemical and other biological characteristics. Detailed depth profiles of the major autotrophic and heterotrophic microplankton groups (bacteria, phytoplankton, microzooplankton) revealed a strong vertical coherence in distribution at both sites, with maximum concentrations in the upper 50 m being typical of the spring bloom. Ultraplankton (< 10 μm) were an important component of the primary producers at 40°N, whereas larger netplankton (diatoms, dinoflagellates) were more important at 45°N. Silicate depletion was clearly evident in surface waters at 45°N, where diatoms were most abundant. Despite the relative importance of diatoms at 45°N, dinoflagellates dominated the biomass of the netplankton at both sites; however, much of this community may have been heterotrophic. Bacterial biomass and production were high at both stations relative to phytoplankton levels, particularly at 45°N, and may have contributed to the unexpectedly high residual ammonium concentrations observed below the chlorophyll maximum layer at both stations. Microzooplankton grazing dominated phytoplankton losses at both stations, with consumption as high as 88% of the daily primary production. Grazing losses to the mesozooplankton, on the other hand, were small (<10%), but mesozooplankton contribution to the vertical flux of organic matter (fecal pellets) was important at 45°N. F-ratios estimated by 15N tracer methods and sediment trap fluxes were similar and suggeste that ∼30% of the daily primary production was lost by direct sedimentation during the observation period. Numerous similarities in bloom characteristics were noted between the western and eastern Atlantic study sites.

Evaluation of N2fixation and N absorption activity by relative ureide method in field-grown soybean plants with deep placement of coated urea

Abstract In order to evaluate the beneficial effect of deep placement of coated urea fertilizer on soybean plant (Glycine max (L.) Merr. cv. Enrei) cultivation, a field experiment was conducted with three fertilizer N treatments: control, conventional basal dressing of 16 kg N ha-1 as ammonium sulfate; basal deep placement of 100 kg N ha-1 as 100 d type coated urea; and top dressing of 100 kg N ha-1 as 70 d type coated urea just before the flowering stage. The seasonal variation in the N2 fixation activity by the nodules and N absorption rates by roots were estimated by the determination of the relative ureide-N abundance in the root bleeding xylem sap by calculating the increase in total N accumulation. The N recovery rate from fertilizers was measured by the 15N tracer method. The N recovery rate in the plants with deep placement of coated urea was about 62%, and much higher than that of the plants with top dressing of coated urea (33%) at the R7 stage. Top dressing treatment depressed the N2 fixation a...

A 15N tracer method for the measurement of dissolved organic nitrogen release by phytoplankton

We present a new method for separation of dissolved organic nitrogen (DON) from dissolved inorganic nitrogen (DIN) in marlne samples which permlts the measurement of DO'*N production during DII5N uptake and regeneration experiments. Ion retardat~on resin was used to separate DI1'N from DOI'N and the isolated D0I5N was subsequently analyzed by mass spectrometry Variat~on in D0I5N atom % enrichment in duplicate samples, determined w ~ t h the ion retardation column method, was less than 40 . We also separated the low n~olecular weight (LMW) from total D015N using ultrafiltration and found the ratio of these variables to be a useful index in determining what release processes were likely occurring in a given sample. Examples are presented from 2 types of experiments conducted in Chesapeake Bay waters: first, a 6 h time-course of D015N release from both NH,' and I5NO3uptake, and second, a series of short-term (0.5 h) release measurements from 15NH,* uptake over the course of a day. In the former, total DO1% release rates resulting from 15NH,* uptake were several-fold higher than those resulting from IsNO3uptake due to extremely low rates of incorporat~on of NO? into cellular organic material. The release of LMW DOI'N resulting from I5NH,+ uptake decreased from 78 to 21 % of total D0I5N release during the 6 h incubation which suggests that processes other than direct release by phytoplankton (e.g. sloppy feeding, cell lysis) likely became more important as the incubation progressed In the latter expenment, LMW DO'% release was 0 to 16 % of total D0I5N release, which indicates that, in this case, also, processes other than direct release by phytoplankton were dominating the flux of DON from phytoplankton.

Mineralization of Nitrogen from Nitrogen‐15 Labeled Crop Residues and Utilization by Rice

AbstractThe availability of N from the residues of the previous crop to the subsequent rice (Oryza sativa L.) crop is largely unknown. The objectives of this study were to (i) measure the mineralization of N from 15N‐labeled rice, soybean (Glycine max L.), and wheat (Triticum aestivum L.) residues and the uptake by a subsequent rice crop; and (ii) compare the 15N tracer method with the standard fertilizer‐N response method used in field studies to quantify the N contribution from the crop residue to the next crop. Nitrogen mineralization from decomposing crop residues was measured by soil sampling prior to seeding the rice crop and after seeding by plant sampling the rice at maturity. The minimum estimate of the amount of residue N mineralized from the time of residue incorporation until rice harvest was 9, 52, and 38% of the rice, soybean, and wheat residue N, respectively. The amount of residue N recovered in the rice crop was 3, 11, and 37% of the rice, soybean, and wheat residue N, respectively. The lower the C/N ratio and the higher the amount of N in the residue, the lower was the amount of residue N recovered in the soil organic fraction at harvest and the higher was the amount of residue N mineralized. The 15N tracer method compared favorably with the fertilizer N response method when the uptake efficiency of the fertilizer N was taken into account.

Immobilization, mineralization and availability to rice plants of nitrogen derived from heterotrophic nitrogen fixation in flooded soil

Abstract The distribution of nitrogen immobilized by heterotrophic N2-fixing microorganisms in anaerobic soils amended with glucose among various components of the soil-N was determined by a 15N tracer method, and the immobilization and mineralization processes were compared with those from ammonium and native soil nitrogen. The availability of biologically fixed-N to wetland rice plants was also investigated. About 66% of the nitrogen originated from N2 and 72% of that from NH4 + was converted to an amino acid-N fraction after 4 days. At 20 days, 7% of the fixed-N and 13% of the applied-N was mineralized. By drying the soils, most of the mineralized-N was re. immobilized to an amino acid-N fraction. These results suggest that biologically fixed-N undergoes transformation processes almost similar to those of immobilized fertilizer-N. The mineralization rates were 23.4% for the fixed-N and 4.6% for the native soil-N after 16 days. The rice plants had absorbed 34% of the fixed-N and 8% of the soil-N in 42 d...

1145 AMMONIA METABOLISM OF A PATIENT WITH ORNITHINE TRANSCARBAMYLASE DEFICIENCY DETECTED BY 15N TRACER METHOD

Glutamine and glutamate are said to serve to remove excess of NH4 in animals. But the detailed relationship in ammonia metabolism between NH4 and amino acids was not known in urea cycle enzymopathies. We investigated the ammonia metabolism of a patient with OTC deficiency (an 8-year-old female) using 15N tracer method. 15NH4Cl was administered orally to the patient (500mg) and a volunteer (lg). The 15N excess ratios of amino acids and urea in the serum were examined during time course after the administration of 15NH4Cl. The 15N excess ratios of amino acids were examined in the form of the N-TFA-O butylester derivatives using gas chromato-mass spectrometry. Urea 15N was assayed using an isotope ratio mass spectrometry. The incorporation of 15N into urea in the patient was decreased to one forth compared to that in the control. The large amount of 15N was incorporated immediately into alanine, asparagine, glutamine(α-N) and glutamate. This pattern is very significant compared to the normal control. But the incorporation of 15NH4C1 into another amino acids in the patient was the same as that in the control. Accordingly, we suggest that alanine and asparagine could serve to remove excess of NH4 in patient with

Dissimilatory reduction of nitrate and nitrite in the bovine rumen: nitrous oxide production and effect of acetylene.

15N tracer methods and gas chromatography coupled to an electron capture detector were used to investigate dissimilatory reduction of nitrate and nitrite by the rumen microbiota of a fistulated cow. Ammonium was the only 15N-labeled end product of quantitative significance. Only traces of nitrous oxide were detected as a product of nitrate reduction; but in experiments with nitrite, up to 0.3% of the added nitrogen accumulated as nitrous oxide, but it was not further reduced. Furthermore, when 13NO3- was incubated with rumen microbiota virtually no [13N]N2 was produced. Acetylene partially inhibited the reduction of nitrite to ammonium as well as the formation of nitrous oxide. It is suggested that in the rumen ecosystem nitrous oxide is a byproduct of dissimilatory nitrite reduction to ammonium rather than a product of denitrification and that the latter process is absent from the rumen habitat.

Capacities of shallow waters of Sagami Bay for oxidation and reduction of inorganic nitrogen

The distribution of nitrite, nitrate and ammonia in Sagami Bay, Japan, was investigated on Cruises KT-70-5 and KT-70-13 of the R.V. Tansei Maru. In summer, the maximum concentration of nitrite (about 0·3 μg atoms N/1. in central Sagami Bay) occurred at 20–30 m depth and was associated with a seasonal thermocline. In winter, the concentrations of nitrite were nearly constant (about 0·3 μg atoms N/1.) from the surface down to about 100 m; below that depth they decreased. The potential activities for nitrite production from nitrate ammonia were measured, using a 15N-tracer method. The activity for nitrite production from nitrate was of the same order of magnitude as that from ammonia (1·4 ng atoms N/1./hour, on an average), irrespective of the season. The capacities for assimilation of inorganic nitrogen in the upper layers (0–50 m) were several times higher than those for the oxidation of ammonia and the reduction of nitrate, but a reverse relation was observed below the euphotic zone. The residence time of nitrite in the upper layers was 7–16 days.

Nitrogen Fixation and the Utilization of Other Inorganic Nitrogen Sources in a Subarctic Lake

A year-round limnological study of the biological utilization of molecular nitrogen, ammonia, and nitrate in Smith Lake, a small subarctic lake in interior Alaska, showed that ammonia was consistently the most important nitrogen source. Of the two main algal production periods, the first took place under the ice in May, and depended on ammonia accumulated during the winter for a nitrogen source. The population at this time consisted largely of microflagellates. Chlamydomonas, Euglena, Chlorella, and Mellamonas were among the identified algae present. Immediately after the ice melted from the lake surface, a second population developed. These algae, consisting almost exclusively of Anabaena flos-aquae, used ammonia, nitrate, and molecular nitrogen simultaneously. During the remainder of the summer, uptake rates remained relatively low, with ammonia the most important nitrogen source; during the fall, nitrate uptake briefly approached the magnitude of ammonia uptake. 15N tracer methods were used to measure the uptake rates in this work.