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PubMed1976

The effects of sweat nitrogen losses in evaluating protein utilization by preadolescent children.

A nitrogen balance study was conducted to determine the effects of three levels of nitrogen intake on the loss of nitrogen through sweat and to assess further the impact of sweat nitrogen on protein needs of preadolescent children. Values were determined through the collection of 24-hr, total body sweat samples from twelve healthy boys having a mean age of 8 years, 8 months. Mean height and weight of the subjects were 131.4 cm and 31.0 kg, respectively. Environmental conditions were relatively constant during the study. Mean sweat nitrogen losses were 208, 287, and 368 mg/day on daily protein intakes of 29, 54, and 84 g, respectively. Mean nitrogen balances per day were 0.39, 0.09, and 1.95 g when sweat nitrogen losses were included in the calculations. At the lower and moderate levels of protein intake, nine and six subjects were in negative nitrogen balance when sweat losses were considered. Sweat nitrogen losses in the boys were similar to a previous study with preadolescent girls. Based upon published basal metabolic rates and mean sweat nitrogen losses of 261 and 288 mg/day for girls and boys, the nitrogen lost through sweat was 0.25 mg/basal kcal for both sexes. An estimation of 0.5 mg/basal kcal for integumental nitrogen loss appears realistic for this age group.

Body Surface Area↗

PubMed2001

Protein requirement of elderly women: nitrogen balance responses to three levels of protein intake.

BACKGROUND: For elderly women, insufficient data exist to assess the accuracy of the assumed mean protein requirement of 0.6 g of protein x kg(-1) x day(-1), and the adequacy of the current Recommended Dietary Allowance (RDA) of 0.8 g of protein x kg(-1) x day(-1). The aims of this study were to assess the mean protein requirement and suggested safe and adequate protein intake (protein allowance) of elderly women using a shorter-term nitrogen balance protocol. METHODS: During three separate 18-day trials, 11 elderly women (age range, 70-81 years) were randomly fed eucaloric diets designed to provide either 0.50, 0.75, or 1.00 g of protein x kg(-1) x day(-1). Nitrogen balance was determined at Weeks 2 and 3 (Days 7-10 and 14-17, respectively) of each trial using data from total nitrogen analyses of duplicate food composites, 24-hour urine collections, and stool collections. The mean protein requirement was calculated using linear regression of individual women's data from all three trials and inverse prediction. RESULTS: At protein intakes of 0.53 +/- 0.02, 0.76 +/- 0.02, or 1.06 +/- 0.05 g of protein x kg(-1) x day(-1), net nitrogen balances during Week 2 were -14.5 +/- 3.1, 3.8 +/- 2.5 and 23.4 +/- 3.3 mg of nitrogen x kg(-1) x day(-1), respectively, for these body weight- and body composition-stable women. At Week 3, the net nitrogen balances were -0.1 +/- 2.7, 8.5 +/- 3.6 and 42.0 +/- 3.0 mg of nitrogen x kg(-1) x day(-1). From Week 2 to Week 3, shifts to more positive nitrogen balances occurred due to decreases in urinary nitrogen excretion. The mean protein requirement at Week 2 was calculated to be 0.70 +/- 0.09 g of protein. kg(-1) x day(-1) (coefficient of variation [CV] = 13%) and at Week 3 was calculated to be 0.56 +/- 0.09 g of protein x kg(-1) x day(-1) (CV = 17%). From these data, an adequate protein allowance was estimated to be greater than the RDA at Week 2 (0.90 g of protein x kg(-1) x day [d](-1)), and not different than the RDA at Week 3 (0.76 g of protein x kg(-1) x d(-1)). CONCLUSIONS: The decrease over time in urinary nitrogen excretion from Week 2 to Week 3 suggests that these elderly women did not achieve a metabolic steady state during this shorter-term nitrogen balance study. Collectively, these data suggest that the total protein needs of elderly women are at or above the current RDA for protein. However, the results of this study indicate that shorter-term nitrogen balance protocols are insufficient to firmly establish the RDA for protein of elderly women, and further research is required using alternative criteria measures.

Aged↗

PubMed2006

Nitrogen emissions from broilers measured by mass balance over eighteen consecutive flocks.

Emission of nitrogen in the form of ammonia from poultry rearing facilities has been an important topic for the poultry industry because of concerns regarding the effects of ammonia on the environment. Sound scientific data is needed to accurately estimate air emissions from poultry operations. Many factors, such as season of the year, ambient temperature and humidity, bird health, and management practices can influence ammonia volatilization from broiler rearing facilities. Precise results are often difficult to attain from commercial facilities, particularly over long periods of time. Therefore, an experiment was conducted to determine nitrogen loss from broilers in a research facility under conditions simulating commercial production for 18 consecutive flocks. Broilers were reared to 40 to 42 d of age and fed diets obtained from a commercial broiler integrator. New rice hulls were used for litter for the first flock, and the same litter was recycled for all subsequent flocks with caked litter removed between flocks. All birds, feeds, and litter materials entering and leaving the facility were quantified, sampled, and analyzed for total nitrogen content. Nitrogen loss was calculated by the mass balance method in which loss was equal to the difference between the nitrogen inputs and the nitrogen outputs. Nitrogen partitioning as a percentage of inputs averaged 15.29, 6.84, 55.52, 1.27, and 21.08% for litter, caked litter, broiler carcasses, mortalities, and nitrogen loss, respectively, over all eighteen flocks. During the production of 18 flocks of broilers on the same recycled litter, the average nitrogen emission rate was calculated to range from 4.13 to 19.74 g of N/ kg of marketed broiler (grams of nitrogen per kilogram) and averaged 11.07 g of N/kg. Nitrogen loss was significantly (P < 0.05) greater for flocks reared in summer vs. winter. Results of this experiment have demonstrated that the rate of nitrogen volatilization from broiler grow-out facilities varies significantly on a flock-to-flock basis.

Air Pollutants↗

PubMedDate not supplied

Evaluation of nitrogen utilization in patients receiving total parenteral nutrition.

This two phase study evaluates nitrogen utilization by the body as a function of fixed caloric intake but different nitrogen loads. Nitrogen use by the body was estimated from measures of nitrogen balance, net protein utilization, and urea accumulation rate. Phase 1 of this study included 411 measurements of nitrogen use in 120 patients assigned, according to clinical condition, to receive one of the four following therapies: dextrose (D) 25%, amino acids (CAA) 4.25% (Group 1); D 35%, CAA 4.25% (Group 2); D 25%, CAA 21.3% (Group 3); or D 35%, CAA 21.3% (Group 4). Forty patients in Phase 2 were assigned in a randomized, prospective, double blind manner, to receive one of the following regimens; D 35%, CAA 2.75% (Group 5); D 25%, CAA 2.75% (Group 6); D 35%, CAA 4.25% (Group 7); or D 25%, CAA 4.25% (Group 8). In Phase 1, positive nitrogen balance was achieved with the exception of Group 3 where neither the estimated caloric nor nitrogen needs of the patients were met. It appeared that protein utilization was maximal in patients receiving the therapy of highest calorie:nitrogen ratio (Group 4). Phase 2 patients achieved positive nitrogen balance to the same extent (p greater than 0.05) and although net protein utilization improved from 53 to 71%/d as the calorie:nitrogen ratio was increased, the differences were not significant (p greater than 0.05). There was a significant improvement in total iron binding capacity in Phase 2 patients (p less than 0.01) that was most prominent at the lower concentrations of amino acids (high cal:n ratio) (Groups 5 and 6). Smaller amounts of nitrogen appear adequate in producing a positive nitrogen balance and may be better utilized in hospitalized patients if the patients' caloric requirements are achieved.

Adolescent↗

PubMedDate not supplied

Modeling atmospheric nitrogen deposition and transport in the Chesapeake Bay watershed.

Atmospheric deposition of nitrate nitrogen and ammonium nitrogen has been identified as a major factor in the decline of water quality in the Chesapeake Bay. Reports have indicated that atmospheric deposition may account for 25 to 80% of the total nitrogen load entering the bay. However, uncertainties exist regarding the accuracy of the atmospheric deposition inputs, nitrogen retention coefficients, and in-stream nutrient uptake rates used in these studies. This project was designed to reassess the potential inputs of atmospheric nitrogen deposition to the bay through the use of a high-resolution wet deposition model, improved wet and dry deposition and nutrient retention estimates, existing soils and land use data, and geographic information systems software. Model results indicate that the methods used in previous studies may overestimate the contribution of atmospheric nitrate and ammonium deposition to the Chesapeake Bay watershed (CBW). Wet and dry atmospheric nitrate and ammonium nitrogen deposition estimates to the CBW ranged from 52.7 to 141.9 and 41.9 to 60.1 million kg/yr, respectively, between 1984 and 1996. Dry and total atmospheric deposition loads to the watershed are substantially less than previous estimates. Estimates of the percent contribution of atmospherically deposited nitrogen to the Chesapeake Bay represent between 20 and 32% of the total nitrate and ammonium nitrogen load to the watershed from all nitrogen sources. While these estimates are lower than many other published estimates, regression analysis of model parameters, nitrogen retention coefficients, output, and measured in-stream nitrogen loads indicate that the calculated nitrogen loads may still be too high.

Atmosphere↗

PubMed1985

Nitrogen distribution in human milk from 2 to 16 weeks postpartum.

The objective of this study was to determine how the major nitrogen components in human milk vary as total nitrogen in the milk changes. Milk samples were collected from 10 mothers at 2, 6, 12, and 16 wk postpartum. The major nitrogen components compared were total, nonprotein, urea, protein, casein, and whey nitrogens. Total nitrogen decreased from 2.18 mg/ml at 2 wk to 1.76 mg/ml at 16 wk. The percentage of nonprotein nitrogen was 19% and remained constant with time postpartum. Urea nitrogen averaged .14 mg/ml and also remained constant. Protein nitrogen decreased from 1.77 mg/ml at 2 wk to 1.42 mg/ml at 16 wk. As the total nitrogen in milk changed, the percentages of nonprotein nitrogen, whey nitrogen, and casein nitrogen remained relatively constant.

Female↗

PubMed2003

[Response of lettuce to different nitrogen forms].

Solution culture experiment was adopted to investigate the influence of different nitrogen forms on lettuce growth and development and their nitrogenous nutritional characteristics. The results showed that the affinity of the roots of lettuce seedlings to ammonium nitrogen (NH4(+)-N) was slightly higher than that to nitrate nitrogen (NO3(-)-N). Among three treatments of NO3(-)-N, NH4(+)-N+ NO3(-)-N and NH4(+)-N, the relative proportion of biological yields of lettuce was 100:56.9:12.4, and that of nitrogen uptake amount was 100:48.9:8.6, respectively. Nitrate nitrogen was the most suitable N source to lettuce growth. When the respective proportion of NH4(+)-N and NO3(-)-N was 50%, the growth of lettuce was inhibited to some extent. When the nitrogen source supplied as solely NH4(+)-N, lettuce was hard to grow normally. When supplying the same amount of NH4(+)-N and NO3(-)-N, lettuce showed a tendency to absorb more NH4(+)-N than NO3-N. At different culture stages, the ratio of NH4(+)-N to NO3(-)-N absorbtion was less than 1. It seemed that lettuce did prefer NH4(+)-N to NO3-N in absorbtion. However, ammonium nitrogen as nitrogen source was not suitable to lettuce for its metabolism. When nitrate nitrogen was not sufficient, it mainly affected the growth of lettuce shoot; when the ammonium nitrogen in nutrient solution was 50%, the root growth of lettuce seedlings was greatly inhibited, and some pathological symptoms appeared. Taking running water as water source (in which, NO3(-)-N concentration was about 0.5 mol.L-1) and lettuce was cultured by supplying sole NO3(-)-N for two weeks and then supplying NH4(+)-N, the growth of lettuce was greatly stimulated, in the meantime, the NO3(-)-N contents and total accumulation amount greatly decreased. Supplying urea as N source, the growth rate of lettuce was apparently inferior to other nitrogen forms, but no pathological symptoms appeared.

Absorption↗

PubMed1992

Nitrogen balances of lean and obese Zucker rats subjected to a cafeteria diet.

The effects of a cafeteria diet on nitrogen balance in lean (Fa/?) and obese Zucker rats (fa/fa) was studied for two consecutive 15 day periods after weaning. Obese rats were able to absorb a lower proportion of dietary nitrogen than the lean controls. Cafeteria diet increased the retention of dietary nitrogen, and lowered urinary nitrogen losses in both obese and lean rats. Urea constituted practically the only product of urinary nitrogen excretion in obese rats, whereas it accounted for only about 75% of that eliminated by Fa/? rats. Nitrogen accretion in the body was highest for the younger animals, and again increased with cafeteria feeding. Obese fa/fa rats showed a lower percentage of body nitrogen retention than their lean counterparts; obese rats were able, however, to accumulate large amounts of nitrogen and fat, in part because of their higher intake. A significant part of the absorbed nitrogen was not found in either the body or the urine; the cafeteria diet markedly increased the weight of this fraction of nitrogen unaccounted for. In conclusion, the effects of cafeteria feeding on weight and nitrogen handling were comparable in lean and obese rats, i.e. the effects of genetic and dietary obesity seem to be additive with regard to nitrogen extraction and excretion for Zucker rats.

Absorption↗

PubMed1989

Altered susceptibility to viral respiratory infection during short-term exposure to nitrogen dioxide.

The studies reported here focus on the relation of nitrogen dioxide exposure to susceptibility to viral respiratory infection in a murine model of pneumonia, created by intratracheal inoculation of an endogenous murine pathogen, mouse cytomegalovirus. The purpose of this work is to clarify the potential role of nitrogen dioxide exposure in the pathogenesis of viral infection of the lower respiratory tract. Previous human epidemiologic studies have presented conflicting information about the relationship of nitrogen dioxide to acute, self-limited episodes of respiratory illness, which are characteristic of viral respiratory infection. Some studies have found an association between exposure to elevated ambient levels of nitrogen dioxide and increased occurrence of acute respiratory illness. In one study this association was found to be strongest in children in the first two years of life. However, other epidemiologic studies have failed to observe this relation. To determine if there is scientific evidence for the possible relation of nitrogen dioxide exposure to human respiratory infection, our studies were performed to assess the impact of nitrogen dioxide on respiratory tract susceptibility to initial, or primary, infection, as well as to recurrent infection, or reinfection, with the identical virus. The latter mechanism of viral respiratory infection is of particular interest, since reinfection is a common method for the development of infection of the lower respiratory tract during early childhood. Outbred CD-1 mice were exposed to either air or nitrogen dioxide for six hours a day on two consecutive days prior to inoculation with murine cytomegalovirus, and then were reexposed to the same level of nitrogen dioxide for six hours a day on four consecutive days, beginning the day after viral inoculation. Susceptibility to primary infection was determined by inoculating animals with an amount of virus (10(2) plaque-forming units) that is too small to produce viral infection in the lungs of normal animals. Mice exposed to 5 parts per million (ppm) nitrogen dioxide routinely developed viral replication in the lung and histologic evidence of pneumonitis after inoculation with this amount of virus, whereas air-exposed animals did not. Most importantly, animals exposed to 5 ppm nitrogen dioxide could be infected with a viral inoculum that was 100-fold smaller than that required to consistently produce viral infection in air-exposed mice. Enhanced susceptibility to infection was found after exposure to 5 ppm nitrogen dioxide, but was not observed with exposure to 2.5 or 1 ppm nitrogen dioxide.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Susceptibility to virus infection with exposure to nitrogen dioxide.

The interaction between nitrogen dioxide (NO2) exposure and human susceptibility to respiratory virus infection was investigated in a placebo-controlled, randomized, blinded trial that was conducted in an environmentally controlled research chamber over a three-year period. Healthy, non-smoking volunteers, 18 to 35 years old, who were seronegative to influenza A/Korea/82 (H3N2) virus, were randomly assigned either to breathe filtered clean air (clean air group) or nitrogen dioxide (exposure group) for two hours a day for three consecutive days. The nitrogen dioxide concentrations were 2 ppm (Year 1), 3 ppm (Year 2), and 1 or 2 ppm (Year 3). Live, attenuated cold-adapted (ca) influenza A/Korea/82 reassortant virus was administered intranasally to all subjects after the second day of exposure. Only one of the 152 volunteers had any symptoms, and that subject had only a low-grade fever. No adverse changes in pulmonary function or nonspecific airway reactivity to methacholine were observed after 2 or 3 ppm nitrogen dioxide exposure, virus infection, or both. Infection was defined by virus recovery, a four-fold or greater increase in serum or nasal wash influenza-specific antibody titers, or both. The infection rates of the groups exposed to nitrogen dioxide and those breathing clean air were: 12/21 (2 ppm nitrogen dioxide) versus 15/23 (clean air) in Year 1; 17/22 (3 ppm nitrogen dioxide) versus 15/21 (clean air) in Year 2; and 20/22 (2 ppm nitrogen dioxide) and 20/22 (1 ppm nitrogen dioxide) versus 15/21 (clean air) in Year 3. Although the differences were not statistically significant, the groups exposed to 1 or 2 ppm nitrogen dioxide in the last year became infected more often (91 percent) than those breathing clean air (71 percent). The frequencies of infection in two of the four groups exposed to nitrogen dioxide were higher than the 56 to 73 percent infection rate observed in previous studies in healthy human volunteers with the same dose of ca-influenza A (H3N2) virus. Our findings suggest, but do not prove, that nitrogen dioxide alone may play a role in increasing the susceptibility of adults to respiratory virus infections.

Adolescent↗

PubMed1993

Nitrogen dioxide and respiratory illness in children. Part I: Health outcomes.

We have carried out a prospective cohort study to test the hypothesis that exposure to nitrogen dioxide increases the incidence and severity of respiratory infections during the first 18 months of life. Between January 1988 and June 1990, 1,315 infants were enrolled into the study at birth and followed with prospective surveillance for the occurrence of respiratory infections and monitoring of nitrogen dioxide concentrations in their homes. The subjects were healthy infants from homes without smokers; they were selected with stratification by type of cooking stove at a ratio of four to one for gas and electric stoves. Illness experience was monitored by a daily diary of symptoms completed by the mother and a telephone interview conducted every two weeks. Illnesses with wheezing or wet cough were classified as involving the lower respiratory tract; all other respiratory illnesses were designated as involving the upper respiratory tract. Exposure to nitrogen dioxide was estimated by two-week average concentrations measured in the subjects' bedrooms with passive samplers. This analysis is limited to the 1,205 subjects completing at least one month of observation; of these, 823 completed the full protocol, contributing 82.8% of the total number of days during which the subjects were under observation. Incidence rates for all respiratory illnesses, all upper respiratory illness, all lower respiratory illnesses, and lower respiratory illness further divided into those with any wheezing, or wet cough without wheezing, were examined within strata of nitrogen dioxide exposure at the time of the illness, nitrogen dioxide exposure during the prior month, and type of cooking stove. Consistent trends of increasing illness incidence rates with increasing exposure to nitrogen dioxide were not evident for either the lagged or unlagged exposure variables. The effect of nitrogen dioxide exposure on illness occurrence during at-risk intervals of two weeks' duration was examined using the generalized estimating equation approach. In these multivariate analyses, none of the odds ratios was significantly elevated for unlagged nitrogen dioxide exposures, lagged nitrogen dioxide exposures, or stove type. Duration of illness was assessed in relation to the same exposure variables; illness duration and nitrogen dioxide exposure were not associated. We have found that indoor exposure to nitrogen dioxide is associated with neither the incidence nor the duration of respiratory illnesses. The study was designed to have sufficient power to detect effects of nitrogen dioxide exposure of magnitudes previously reported and in a range relevant to public health concern; the lack of association cannot be attributed to potential bias from misclassification of outcome or exposure.(ABSTRACT TRUNCATED AT 400 WORDS)

Air Pollutants↗

PubMed1965

NITROGEN FIXATION BY MEMBERS OF THE TRIBE KLEBSIELLEAE.

Mahl, M. C. (University of Wisconsin, Madison), P. W. Wilson, M. A. Fife, and W. H. Ewing. Nitrogen fixation by members of the tribe Klebsielleae. J. Bacteriol. 89:1482-1487. 1965.-Strains of species of the tribe Klebsielleae were tested for nitrogen fixation by inoculating actively growing cultures into side-arm flasks containing a medium with a growth-limiting quantity of combined nitrogen (25 mug of nitrogen per ml as ammonium sulfate). The flasks were evacuated, filled with pure N(2), sealed, and placed on a shaker at 30 C. Growth was followed by optical-density measurements; maximal growth was obtained in 9 to 10 hr. Yeast extract was then added as a source of amino acids to shorten the induction time for the nitrogen-fixing enzymes. Fixation was determined either by estimating total nitrogen with a semimicro Kjeldahl technique or by exposing 20- to 22-hr-old samples to an atmosphere of N(2) (15) and helium for 5 hr and then analyzing the digested sample for N(15) in a mass spectrometer. None of the 22 strains of the two Enterobacter (formerly Aerobacter) species fixed nitrogen; neither did any of eight strains of Serratia species that were tested. Of 31 strains of Klebsiella pneumoniae, 13 incorporated atmospheric nitrogen. Net nitrogen fixed ranged from 17 to 65 mug/ml. It is concluded that these facultative anaerobic, gram-negative, nitrogen-fixing rods should be placed in the genus Klebsiella pneumoniae. The nitrogen-fixing organism tentatively classified as Achromobacter N-4 should also be changed to K. pneumoniae strain N-4, because it has been found to be an anaerogenic strain of K. pneumoniae.

Achromobacter↗

PubMed1997

Effects of elevated CO2, nitrogen supply and tropospheric ozone on spring wheat-II. Nutrients (N, P, K, S, Ca, Mg, Fe, Mn, Zn).

CO(2) enrichment is expected to alter leaf demand for nitrogen and phosphorus in plant species with C(3) carbon dioxide fixation pathway, thus possibly causing nutrient imbalances in the tissues and disturbance of distribution and redistribution patterns within the plants. To test the influence of CO(2) enrichment and elevated tropospheric ozone in combination with different nitrogen supply, spring wheat (Tritium aestivum L. cv. Minaret) was exposed to three levels of CO(2) (361, 523, and 639 microl litre(-1), 24 h mean from sowing to final harvest), two levels of ozone (28.4 and 51.3 nl litre(-1)) and two levels of nitrogen supply (150 and 270 kg ha(-1)) in a full-factorial design in open-top field chambers. Additional fertilization experiments (120, 210, and 330 kg N ha(-1)) were carried out at low and high CO(2) levels. Macronutrients (N, P, K, S, Ca, Mg) and three micronutrients (Mn, Fe, Zn) were analysed in samples obtained at three different developmental stages: beginning of shoot elongation, anthesis, and ripening. At each harvest, plant samples were separated into different organs (green and senescent leaves, stem sections, ears, grains). According to analyses of tissue concentrations at the beginning of shoot elongation, the plants were sufficiently equipped with nutrients. Elevated ozone levels neither affected tissue concentrations nor shoot uptake of the nutrients. CO(2) and nitrogen treatments affected nutrient uptake, distribution and redistribution in a complex manner. CO(2) enrichment increased nitrogen-use efficiency and caused a lower demand for nitrogen in green tissues which was reflected in a decrease of critical nitrogen concentrations, lower leaf nitrogen concentrations and lower nitrogen pools in the leaves. Since grain nitrogen uptake during grain filling depended completely on redistribution from vegetative pools in green tissues, grain nitrogen concentrations fell considerably with severe implications for grain quality. Ca, S, Mg and Zn in green tissues were influenced by CO(2) enrichment in a similar manner to nitrogen. Phosphorus concentrations in green tissues, on the other hand, were not, or only slightly, affected by elevated CO(2). In stems, 'dilution' of all nutrients except manganese was observed, caused by the huge accumulation of water soluble carbohydrates, mainly fructans, in these tissues under CO(2) enrichment. Whole shoot uptake was either remarkably increased (K, Mn, P, Mg), nearly unaffected (N, S, Fe, Zn) or decreased (Ca) under CO(2) enrichment. Thus, nutrient cycling in plant-soil systems is expected to be altered under CO(2) enrichment.

Journal Article↗

PubMed1997

Equilibration of the terrestrial water, nitrogen, and carbon cycles.

Recent advances in biologically based ecosystem models of the coupled terrestrial, hydrological, carbon, and nutrient cycles have provided new perspectives on the terrestrial biosphere's behavior globally, over a range of time scales. We used the terrestrial ecosystem model Century to examine relationships between carbon, nitrogen, and water dynamics. The model, run to a quasi-steady-state, shows strong correlations between carbon, water, and nitrogen fluxes that lead to equilibration of water/energy and nitrogen limitation of net primary productivity. This occurs because as the water flux increases, the potentials for carbon uptake (photosynthesis), and inputs and losses of nitrogen, all increase. As the flux of carbon increases, the amount of nitrogen that can be captured into organic matter and then recycled also increases. Because most plant-available nitrogen is derived from internal recycling, this latter process is critical to sustaining high productivity in environments where water and energy are plentiful. At steady-state, water/energy and nitrogen limitation "equilibrate," but because the water, carbon, and nitrogen cycles have different response times, inclusion of nitrogen cycling into ecosystem models adds behavior at longer time scales than in purely biophysical models. The tight correlations among nitrogen fluxes with evapotranspiration implies that either climate change or changes to nitrogen inputs (from fertilization or air pollution) will have large and long-lived effects on both productivity and nitrogen losses through hydrological and trace gas pathways. Comprehensive analyses of the role of ecosystems in the carbon cycle must consider mechanisms that arise from the interaction of the hydrological, carbon, and nutrient cycles in ecosystems.

Journal Article↗

PubMed1981

Nitrogen Starvation and the Regulation of Glutamine Synthetase in Agmenellum quadruplicatum.

The level of glutamine synthetase activity in Agmenellum quadruplicatum strain PR-6 was dependent on the nitrogen source used for growth and on the nutritional status of the cells. During exponential growth, glutamine synthetase activity was low in cells grown on ammonia, urea, or nitrate. During the transition from nitrogen replete to nitrogen starved growth, glutamine synthetase activity began to rise. With ammonia as a nitrogen source, glutamine synthetase activity as determined in whole cells increased from 1 nanomole per minute per milliliter during exponential growth to 22 nanomoles per minute per milliliter during severe nitrogen starvation. In cells grown on nitrate the increase was from 5 to 39 nanomoles per minute per milliliter, and in cells grown on urea the increase was from 4 to 31 nanomoles per minute per milliliter.The rise in glutamine synthetase activity corresponded with the rapid decline in the nitrogen and c-phycocyanin content of the cells. Prior to nitrogen starvation, the nitrogen content of the cells was 140, 90, and 83 micrograms nitrogen per milligram dry weight for ammonia, urea, and nitrate grown cells, respectively. During nitrogen starvation where glutamine synthetase activity was highest, the nitrogen content of cells had declined to 35 to 40 micrograms nitrogen per milligram dry weight of cells. At the same time, the c-phycocyanin content of cells dropped by 95%.

Journal Article↗

PubMed1983

Nitrogen Turnover and Assimilation during Regrowth in Trifolium subterraneum L. and Bromus mollis L.

Subterranean clover (Trifolium subterraneum L. cv Woogenellup) and soft chess grass (Bromus mollis L. cv Blando) were grown in monocultures with (15)NH(4)Cl added to the soil to study nitrogen movement during regrowth following shoot removal. Four clipping treatments were imposed. Essentially all available (15)N was assimilated from the soil prior to the first shoot harvest. Measurements of total reduced nitrogen and (15)N contained within that nitrogen fraction in roots, crowns, and shoots at each harvest showed large, significant (P </= 0.001) declines in excess (15)N of crowns and roots in both species between the first and fourth harvests. There was no significant decline in total reduced nitrogen in the same organs over that period. Similar responses were evident in plants defoliated three times. The simplest interpretation of these data is that reduced nitrogen compounds turn over in plant roots and crowns during shoot regrowth. Calculations for grass and clover plants clipped four times during the growing season indicated that 100 to 143% of the nitrogen present in crowns and roots turned over between the first and fourth shoot harvest in both species, assuming nitrogen in those organs was replaced with nitrogen containing the lowest available concentration of (15)N. If other potential sources of nitrogen were used for the calculations, it was necessary to postulate that larger amounts of total nitrogen flowed through the crown and root to produce the measured dilution of (15)N compounds. These data provide the first quantitative estimates of the amount of internal nitrogen used by plants, in addition to soil nitrogen or N(2), to regenerate shoots after defoliation.

Journal Article↗

PubMed1990

Effect of Nitrogen Starvation on Polypeptide Composition, Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase, and Thylakoid Carotenoprotein Content of Synechocystis sp. Strain PCC6308.

Synechocystis sp. strain PCC6308 cells were starved for nitrogen for 5 days. The polypeptide compositions of whole cell extracts and washed membranes of nitrogen-replete and nitrogen-starved cells were compared by one- and two-dimensional electrophoresis. Immunoblotting of one-dimensional gels indicated that pelletable ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was depleted in cells starved for nitrogen, while levels of soluble Rubisco were comparable in nitrogen-starved and nitrogen-replete cells. This is consistent with the hypothesis that pelletable Rubisco may serve as a nitrogen reserve in Synechocystis 6308. Other polypeptides were differentially enriched in the membrane or soluble fractions of nitrogen-replete cells or nitrogen-starved cells, suggesting nitrogen starvation may alter partitioning of polypeptides into soluble and membrane fractions. Degradation of abundant polypeptides during nitrogen starvation appeared to cause an effective magnification of less abundant polypeptides in the molecular mass range of 20 to 40 kilodaltons, as shown by two-dimensional electrophoresis. A 42-kilodalton thylakoid carotenoid protein identified by immunoblotting was conserved in membranes from nitrogen-starved cells. This may be functional for cells depleted of pigment and thus exposed to higher light levels because of decreased self-shading.

Journal Article↗

PubMed1996

Salmonella typhimurium apparently perceives external nitrogen limitation as internal glutamine limitation.

Assimilation of nitrogen requires the synthesis of only two central intermediates, glutamate and glutamine, from which other compounds derive nitrogen by secondary transfers. We measured the internal pool sizes of glutamate and glutamine in Salmonella typhimurium under conditions of external nitrogen limitation or sufficiency. When growth was slowed by nitrogen limitation, the glutamine pool was lower by a factor of up to 10, whereas the glutamate pool remained high. The decrease in the glutamine pool was general in nature, being seen with various limiting nitrogen sources in batch culture and with ammonia, the optimal nitrogen source, as the limiting nutrient in continuous culture. The only nitrogen source that gave discordant results was alanine, and we present evidence that alanine has inhibitory effects which extend beyond simple nitrogen limitation. Studies with mutant strains having altered nitrogen assimilation indicated that the decreases in the glutamine pool observed in the wild-type strain under nitrogen-limiting conditions were probably sufficient to account for slow growth and were likely to be responsible for slow growth. Hence we postulate that external nitrogen limitation is first perceived by Salmonella as a drop in its internal glutamine pool.

Alanine↗