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PubMed2001

Microbiological, molecular biological and stable isotopic evidence for nitrogen fixation in the open waters of Lake Michigan.

We have used a combination of microbiological, molecular biological and stable isotope methods to relate specific microbial populations to elemental cycling at an offshore site in Lake Michigan. Several lines of evidence suggest that atmospheric N2 may be a significant source of nitrogen to the lake. Particulate organic nitrogen (PON) at approximately equals 10-15m depth in July and October had a delta15N of 0.5-1.5%o. These values closely reflect the 15N composition of atmospheric N2, suggesting biological nitrogen fixation. Historical data show a developing late-summer N:P minimum at approximately equals 15 m; low abundance of inorganic nitrogen relative to phosphorus favours species able to acquire atmospheric nitrogen. Microscopic examination of October water samples revealed abundant heterocystous cyanobacteria, including Nodularia sp. Potentially nitrogen-fixing Anabaena spp. have been found in Lake Michigan before but, to our knowledge, this is the first report of Nodularia. Finally, we have amplified both cyanobacterial and non-cyanobacterial nifH sequences (encoding the nitrogenase iron protein) from lakewater samples, evidence for the presence of bacteria capable of nitrogen fixation. The surface waters of Lake Michigan are considered to be phosphate limited in the stratified season and, under these conditions, energetically expensive nitrogen fixation is expected to be uncompetitive with assimilation of combined nitrogen. Our results suggest that, from both microbiological and biogeochemical perspectives, this may be an oversimplification.

Animals↗
PubMed2004

(15)N investigation of nitrogen released from tobacco-waste to be utilized by maize crop.

The (15)N study aimed to estimate the portion of nitrogen released from tobacco-waste to be utilized by maize crop. Tobacco-waste at the levels of 0, 2, 4, 6 and 8 g pot(-1) and ((15)NH(4))(2)SO(4) as nitrogen fertilizer labelled with 5 at.% exc. at the levels of 0, 4, 8, 12 and 16 mg N pot(-1) together with a basal dressing of some nutrients were added to pots with Pioneer maize variety. After the harvest, dry matter yield was recorded and (15)N determinations and calculations were made. Tobacco-waste had a positive effect on the growth and on the nitrogen uptake of maize crop. Increasing the rates of tobacco-waste increased the dry matter yield of maize crop from 4.64 g pot(-1) (at control) to 7.22 g pot(-1) (at the tobacco-waste treatment of 8 g pot(-1)). The values of (15)N in the plant derived from nitrogenous fertilizer also increased with increasing nitrogen fertilizer levels, whereas they decreased from 0.427 % to 0.249 % with increasing tobacco-waste treatments from 0 to 8 g pot(-1), respectively. The average values of per cent nitrogen derived from nitrogenous fertilizer (Ndff) varied from 4.32 % to 7.95 % at the rates of 4-16 mg N pot(-1), respec-tively. However, Ndff decreased from 8.54 % to 4.99 % with increasing tobacco-waste treatments from 0 to 8 g pot(-1), respectively. Per cent nitrogen derived from tobacco-waste (Ndft) increased from 21.8 % to 38.5 % with increasing tobacco-waste treatments from 2 to 8 g pot(-1), respectively. The results have revealed that (15)N tracer technique was confidently used for the investigation of nitrogen levels released from tobacco-waste as organic waste to be utilized by maize crop.

Agriculture↗
PubMed1995

Cereal feeding and its impact on the nitrogen economy of the infant.

To quantify the effect of rice cereal on nitrogen balance and fecal nitrogen excretion, and the contribution of endogenous nitrogen sources to fecal nitrogen output, nine infants aged 3-5 mo received [15N]glycine in all feedings. Samples of urine and feces were obtained daily and analyzed for nitrogen and 15N. On days 1-7 the infants received only formula, and a complete urine and fecal collection was made on days 6-7. From days 8 to 12 the formula was supplemented with rice cereal (133.3 g/L, or 4 g/30 mL formula) and a second complete urine and fecal collection was made on days 11-12. Cereal did not alter fecal nitrogen output or the calculated contribution (45%) of endogenous nitrogen to fecal nitrogen. Cereal did increase nitrogen retention and lower the urinary excretion of the 15N dose (24% of dose). The calculated true digestibility of the rice cereal protein was > 95%. Our results indicate that infants aged 4 mo, in contrast with younger infants, are able to digest and absorb cereal. The addition of cereal to the diet does not lead to increased fecal protein losses.

Bacteria↗
PubMed1998

Opposite fluxes of glutamine and alanine in the splanchnic area are an efficient mechanism for nitrogen sparing in rats.

Glutamine release by the liver constitutes a process of nitrogen salvage through the recycling of a part of the nitrogen, which prevents irreversible nitrogen losses as urea. The aim of this work was to study the nitrogen cycling in the splanchnic bed under different nutritional conditions: fed state, postabsorptive state (16 h food deprivation) or prolonged starvation (24 or 40 h). Rats were adapted to a 15% casein diet for 15 d and then sampled. The digestive, hepatic and splanchnic balances of glucose, lactate, ketone bodies, urea and amino acids were determined. There was a net release of lactate and alanine by the digestive tract, due to the high rate of glycolysis and glutaminolysis. During prolonged starvation, ketone bodies became major energy fuel for the intestine. In fed rats, there was a net uptake of most amino acids by the liver, except for glutamine and glutamate. Urea, glutamine and glutamate released represented 33, 24 and 6% of total nitrogen taken up by the liver, respectively. In postabsorptive rats, compared with fed rats, there was a significant reduction of ureagenesis, and glutamine became the major form of nitrogen released by the liver. In fact, nitrogen cycling in the form of glutamine or glutamate in the liver may be interpreted as a nitrogen salvage process, rather than as an acid-base control process. In the splanchnic area, in parallel with a highly active cycling of glucose as lactate, there exists a nitrogen cycling involving opposite fluxes of glutamine and alanine.

Alanine↗
PubMed2002

The Asian nitrogen cycle case study.

We analyzed nitrogen budgets at national and regional levels on a timeline from 1961-2030 using a model, IAP-N 1.0. The model was designed based upon the Inter-governmental Panel on Climate Change (IPCC) methods using Asia-specific parameters and a Food and Agriculture Organization of the United Nations (FAO) database. In this paper we discuss new reactive-nitrogen and its various fates, and environmental nitrogen enrichment and its driving forces. The anthropogenic reactive nitrogen of Asia dramatically increased from approximately 14.4 Tg N yr-1 in 1961 to approximately 67.7 Tg N yr-1 in 2000 and is likely to be 105.3 Tg N yr-1 by 2030. Most of the anthropogenic reactive-nitrogen has accumulated in the environment. We found that an increasing demand for food and energy supplies and the lack of effective measures to improve the efficiency of fertilizer nitrogen use, as well as effective measures for the prevention of NOx emissions from fossil-fuel combustion, are the principal drivers behind the environmental nitrogen-enrichment problem. This problem may be finally solved by substituting synthetic nitrogen fertilizers with new high-efficiency nitrogen sources, but solutions are dependent on advances in biological technology.

Asia↗
PubMed1997

A simple mass balance model of nitrogen flow in a bioregenerative life support system.

A mathematical model of the nitrogen cycle in a bioregenerative life support system (BLSS) was developed to help conceptualize and quantify nitrogen flux and storage in BLSS processes and subsystems. The mathematical model was initially designed as a simple mass balance, donor-controlled system that quantified the amount of nitrogen in moles per person. Dynamic equations were then applied to describe certain relationships more accurately. Comparison of nitrogen fluxes suggests that even at very low atmospheric leakage rates, loss of nitrogen gas would account for the largest nitrogen movement in the "closed" system. This observation decreases the relative importance of denitrification and nitrification in closed system nitrogen balances. Sensitivity analysis was used to determine the relative stability of various model subsystems, and demonstrated the importance of plant nitrogen uptake on overall system dynamics of nitrogen.

Animals↗
PubMed1994

Activation of trehalase during growth induction by nitrogen sources in the yeast Saccharomyces cerevisiae depends on the free catalytic subunits of cAMP-dependent protein kinase, but not on functional Ras proteins.

Addition of a nitrogen-source to glucose-repressed, nitrogen-starved G0 cells of the yeast Saccharomyces cerevisiae in the presence of a fermentable carbon source induces growth and causes within a few minutes a five-fold, protein-synthesis-independent increase in the activity of trehalase. Nitrogen-activated trehalase could be deactivated in vitro by alkaline phosphatase treatment, supporting the idea that the activation is triggered by phosphorylation. Yeast strains containing only one of the three TPK genes (which encode the catalytic subunit of cAMP-dependent protein kinase) showed different degrees of nitrogen-induced trehalase activation. The order of effectiveness was different from that previously reported for glucose-induced activation of trehalase in glucose-depressed yeast cells. Further reduction of TPK-encoded catalytic subunit activity by partially inactivating point mutations in the remaining TPK gene further diminished nitrogen-induced trehalase activation, while deletion of the BCY1 gene (which encodes the regulatory subunit) in the same strains resulted in an increase in the extent of activation. Deletion of the RAS genes in such a tpkw1 bcy1 strain had no effect. These results are consistent with mediation of nitrogen-induced trehalase activation by the free catalytic subunits alone. They support our previous conclusion that cAMP does not act as second messenger in this nitrogen-induced activation process and our suggestion that a novel nitrogen-induced signaling pathway integrates with the cAMP pathway at the level of the free catalytic subunits of protein kinase A. Western blot experiments showed that the differences in the extent of trehalase activation were not due to differences in trehalase expression. On the other hand, we cannot completely exclude that protein kinase A influences the nitrogen-induced activation mechanism itself rather than acting directly on trehalase. However, any such alternative explanation requires the existence of an additional, yet unknown, mechanism for activation of trehalase besides the well-established regulation by protein kinase A.

Amino Acids↗
PubMed2001

Maintenance nitrogen requirement of an obligate nectarivore, the honey possum, Tarsipes rostratus.

A nitrogen balance feeding trial was carried out with the marsupial honey possum, Tarsipes rostratus, using four pollen-honey diets varying in nitrogen content from 9.4 mg.g(-1) to 2.3 mg.g(-1) dry matter. The dietary maintenance nitrogen requirement (MNR) was determined by regression analysis as 89 +/- 21 mg N.kg(-0.75).day(-1) and the truly digestible MNR was 79 mg N.kg(-0.75).day(-1). Regressing nitrogen balance on daily nitrogen intake separately for ten males and seven females revealed that the slopes of the fitted lines did not vary significantly, but the difference in the intercepts approached significance. This suggests that the MNR for females may be lower than that of males. The nitrogen digestibility of the diet was 76% and the biological value (BV) was 58%. A comparison of the MNR of the honey possum with that of other marsupials shows that it is indeed much lower than that of herbivorous macropodid marsupials and is close to that of the sap- and gum-feeding sugar glider, Petarurus breviceps. The endogenous urinary nitrogen excretion (EUN) of the honey possum was 42 mg N.kg(-0.75.day(-1) and a regression analysis with other published data showed that the EUN per unit basal heat production is significantly lower than that of eutherian mammals. Measurements of the actual feeding rates of animals in the field, taken together with the low MNR, do not lend support to the hypothesis that the honey possum exhibits a reduced rate of reproduction due to a deficiency in dietary nitrogen. It is possible that the quality of nitrogen provided by pollen, as reflected in its composition of essential amino acids, may be a limiting factor.

Animals↗
PubMed2003

Intraspecific litter diversity and nitrogen deposition affect nutrient dynamics and soil respiration.

Anthropogenic forces are concurrently reducing biodiversity and altering terrestrial nutrient cycles. As natural populations decline, genetic diversity within single species also declines. The consequences of intraspecific genetic loss for ecosystem functions are poorly understood, and interactions among intraspecific diversity, nitrogen deposition, and nutrient cycling are unknown. We present results from an experiment that simulated both a decline in biodiversity and an increase in nitrogen deposition. In soil microcosms, we tested effects of variation in intraspecific litter diversity and nitrogen deposition on soil respiration and nitrogen leaching. Increases in intraspecific litter diversity increased soil respiration overall, with the greatest increases in respiration occurring under high nitrogen deposition. Nitrogen deposition increased the amount of inorganic nitrogen leached, while the amount of dissolved organic nitrogen leached was correlated with initial litter chemistry (lignin concentration) and remained independent of litter diversity and nitrogen deposition treatments. Our results demonstrate the potential for losses in genetic diversity to interact with other global environmental changes to influence terrestrial nutrient cycles.

Ecosystem↗
PubMed2006

Consequences of nitrogen and phosphorus limitation for the performance of two planthoppers with divergent life-history strategies.

Phytophagous insects have a much higher nitrogen and phosphorus content than their host plants, an elemental mismatch that places inherent constraints on meeting nutritional requirements. Although nitrogen limitation is well documented in insect herbivores, phosphorus limitation is poorly studied. Using factorial experiments in the laboratory and field, in which levels of soil nitrogen and phosphorus were manipulated, we studied the relative consequences of macronutrient limitation for two herbivores, namely the phloem-feeding planthoppers Prokelisia dolus and P. marginata. These planthoppers inhabit the salt marshes of North America where large stands of their Spartina host plant are found. Notably, these congeners differ in their dispersal abilities; P. marginata is dispersive whereas P. dolus is sedentary. Both nitrogen and phosphorus subsidies enhanced the nitrogen and phosphorus content of Spartina. When P. dolus and P. marginata were raised on plants with an enriched nitrogen signature, they exhibited greater survival, grew to a larger size, developed more rapidly, and achieved higher densities than on nitrogen-deficient plants. However, P. marginata experienced greater fitness penalties than P. dolus on nitrogen-deficient plants. Phosphorus limitation and associated fitness penalties were not as severe as nitrogen limitation for P. marginata, and were not detected in P. dolus. The tempered response of P. dolus to N- and P-deficient Spartina is probably due to its greater investment in feeding musculature and hence ability to compensate for nutrient deficiencies with increased ingestion. To cope with deteriorating plant quality, P. dolus employs compensatory feeding, whereas P. marginata disperses to higher quality Spartina. When its option of dispersal is eliminated and P. marginata is confined on nutrient-deficient plants, its performance is drastically reduced compared with P. dolus. This research highlights the importance of interfacing herbivore life-history strategies with ecological stoichiometry in order to interpret the consequences of macronutrient limitation on herbivore performance and population dynamics.

Animals↗
PubMed1993

Nitrogen balance in patients treated with extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) is a commonly used technique in the management of newborn respiratory failure. However, few studies have addressed the optimal nutritional support of these critically ill neonates. Eleven newborns undergoing ECMO for respiratory failure were studied at various levels of intravenous caloric and nitrogen intake, using nitrogen balance techniques, to assess optimal nutritional support necessary to achieve positive nitrogen balance. Nonprotein nitrogen calories > 60 kcal/kg/d, and nitrogen > 240 mg/kg/d were necessary to achieve positive nitrogen balance, while maximum positive balance was seen with nitrogen intake > 400 mg/kg/d. These data suggest that newborns treated with ECMO can achieve positive nitrogen balance with modest amounts of caloric and nitrogen intake.

Energy Intake↗
PubMed1995

Nitrogen mustard drug resistant B-cell chronic lymphocytic leukemia as an in vivo model for crosslinking agent resistance.

Acquired resistance is a limiting factor in chemotherapy. We have employed nitrogen mustard resistant B-cell chronic lymphocytic leukemia (B-CLL) as a clinically relevant model to study this phenomenon. Resistance in B-CLL is associated with enhanced repair of nitrogen mustard crosslinks. In order to identify the repair pathway responsible for nitrogen mustard resistance, lymphocytes were screened for cross-resistance to a variety of DNA damaging agents. The MTT assay was used to measure the resistance of B-CLL lymphocytes to various DNA damaging agents, including nitrogen mustards, UV light, methyl methanesulfonate, and mitomycin C. We have shown that B lymphocytes from patients with nitrogen mustard resistant chronic lymphocytic leukemia reflect their clinical status. This assay allows us to classify lymphocytes as nitrogen mustard sensitive or resistant, based on in vitro observations. The resistant population was 5.6 and 4.1 fold more resistant to the nitrogen mustard analogs, chlorambucil and melphalan, respectively. Resistant lymphocytes displayed no increased resistance to either methyl methanesulfonate or UV light, indicating that neither classical base nor nucleotide excision repair is rate-limiting in resistance. Resistant lymphocytes were 6.0 and 2.2 fold more resistant to mitomycin C and cis-diamminedichloroplatinum (II), respectively, suggesting enhanced crosslink repair. Neither glutathione nor glutathione S-transferase levels correlated with resistance. The development of nitrogen mustard drug resistance in B-CLL appears to be associated with cross-resistance to other bifunctional alkylating agents which produce interstrand crosslinks. Our results indicate that resistance to nitrogen mustards in chronic lymphocytic leukemia is associated with enhanced repair of DNA crosslinks which may involve a recombination dependent system. This model should prove very useful in the elucidation of the molecular mechanisms of crosslink repair.

B-Lymphocytes↗
PubMed1985

Catabolism and nitrogen control in Escherichia coli.

It would appear from these studies that nitrogen control reflects the catabolic capacity of the cell and that utilizable nitrogen sources and some carbon sources are, to some extent, in competition for this capacity. The series of catabolic events initiated by addition of D-amino acids or by growth on aldol sugars, in the presence of ammonia nitrogen in the growth medium, provide an opportunity for study of the positive aspect of nitrogen control under conditions where negative control predominates. This approach may eventually clarify the apparent interactions between the modification cascade components, PII and UT/UR, with the nitrogen regulatory gene, glnG. The utilization of nutrients by E. coli seems less a matter of energy than of expeditious use of whatever is offered in the diet. A comparison of the rate of increase of GS on cultural downshift with the rate of increase following D-glutamate addition would suggest that control by nitrogen limitation is about eight times more effective than positive activation by D-glutamate in the presence of ammonia nitrogen. This observation is consistent with the finding of an additive effect for the D-amino acids which can function as positive activators in GS regulation. It has been demonstrated for the wild-type organism that the increase in GS level generated by a mixture of D-glutamate, D-lysine, D-threonine, and glycine approximates the increase in GS level observed during step-down of the culture from an ammonia-sufficient to an ammonia-limited condition. This observation further supports the physiologic relevance of the effect of D-amino acids in nitrogen control and suggests that the apparent derepression of GS observed upon exhaustion of the ammonia nitrogen supply represents a composite of positive activation generated as alternative catabolic functions assume a greater importance. As might be expected, addition of D-glutamate to cells at the point of ammonia exhaustion had no additional positive effect. Following a downshift from glucose-ammonia-glutamine to glucose-glutamine cultural conditions, only the level of GS increases during the initial 60-minute observation period. This finding suggests that glutamine catabolism may, like D-threonine, D-lysine, and glycine, bypass the positive activation of GDH and GAT controls. The likely possibility in that the increases observed for GAT and GDH depend on D-glutamate as specific inducer. There are several instances where D-amino acids function as inducers of L-amino acid dehydrogenases and where amino acid racemase activity is directly coupled to flavoprotein dehydrogenases.(ABSTRACT TRUNCATED AT 400 WORDS)

Allosteric Regulation↗
PubMed2005

Effects of nitrogen with and without acidified sulphur on an ectomycorrhizal community in a Sitka spruce (Picea sitchensis Bong. Carr) forest.

This preliminary study investigated the effects of enhanced nitrogen (NH4NO3 at 48 kg ha(-1) y(-1)), sulphur (Na2SO4 at 50 kg ha(-1) y(-1)), acidified nitrogen and sulphur (H2SO4 + NH4NO3) at pre-stated doses (pH 2.5), and acidified nitrogen and sulphur deposition at double these doses on the ectomycorrhizal community associated with a 13-year-old Sitka spruce (Picea sitchensis) forest. Sulphur deposition had little impact on below ground ectomycorrhizal diversity, but stimulated sporocarp production. Nitrogen inputs increased below ground colonisation compared to acidified nitrogen and sulphur, largely due to an increase in Tylospora fibrillosa colonisation. Sporocarp production and ectomycorrhizal root colonisation by Lactarius rufus were reduced in the nitrogen treated plots. These observations suggest that nitrogen deposition to a young plantation may suppress ectomycorrhizal fungi producing large sporocarps. It is proposed that enhanced nitrogen deposition increases ectomycorrhizal nitrogen assimilation, consuming more carbon and leaving less for extrametrical mycelium and sporocarp development.

Acid Rain↗
PubMed2006

Evaluating farm performance using agri-environmental indicators: recent experiences for nitrogen management in The Netherlands.

Intensive agriculture, characterized by high inputs, has serious implications on the environment. Monitoring and evaluation of projects aiming at designing, testing and applying more sustainable practices require instruments to asses agronomic as well as environmental performance. Guidelines for Good Agricultural Practice (GAP) or Good Farming Practice (GFP) define sustainable practices but give limited insight into their environmental performance. Agri-environmental indicators (AEIs) provide information on environmental as well as agronomic performance, which allows them to serve as analytical instruments in research and provide thresholds for legislation purposes. Effective AEIs are quantifiable and scientifically sound, relevant, acceptable to target groups, easy to interpret and cost-effective. This paper discusses application of four AEIs for nitrogen (N) management in three Dutch research projects: 'De Marke', 'Cows and Opportunities' and 'Farming with a future'. 'De Marke' applied Nitrogen Surplus and Groundwater Nitrate Concentration in the design and testing of environmentally sound dairy systems. 'Cows and Opportunities', testing and disseminating dairy systems designed at 'De Marke', mainly applied Nitrogen Surplus, while 'Farming with a future' used Nitrogen Surplus, Groundwater Nitrate Concentration and Residual Mineral Soil Nitrogen to support arable farmers in complying with Dutch legislation (MINAS). Nitrogen Surplus is quantifiable, appealing and easy to interpret, but lacks scientific soundness or a good relationship with groundwater quality. Nitrogen Use Efficiency is sensitive to changes in management, while Residual Mineral Soil Nitrogen is appealing and cheap, but has difficulties in scaling. Groundwater Nitrate Concentration lacks clear rules for sampling, is labor consuming, expensive and mainly used in combination with other indicators. AEIs enhanced improvements in N management by facilitating (i) definition of project goals, (ii) design of desired systems, (iii) evaluation of applied systems and (iv) improving effective communication. AEI applications in other countries show a similar pattern as found in The Netherlands. Limitations to AEI application relate to inconsistencies between different indicators, heterogeneity of soil characteristics and linkages of N, carbon and water management. AEIs should be applied in an integrated evaluation, at a scale that reflects the farm's spatial variability. Simple AEIs like Nitrogen Surplus should be supported by other indicators and/or model calculations. The paper concludes that AEIs proved their value in design, implementation and testing of farming systems, but they should be used with care, always keeping in mind that indicators are simplifications of complex and variable processes.

Agriculture↗
PubMed2005

Nitrogen composition in urban runoff--implications for stormwater management.

A study was conducted to characterise the composition of nitrogen in urban stormwater in Melbourne, Australia, during baseflows and storm events, and to compare the results with international data. Nitrogen in Melbourne stormwater was predominantly dissolved (approximately 80%), with ammonia the least-abundant form (approximately 11%). Concentrations of nitrogen species did not vary significantly between baseflow and storms, although the proportion of nitrogen in particulate form was higher during storm events (p = 0.04). Whilst the composition of nitrogen in Melbourne was broadly consistent with international data, the level of dissolved inorganic nitrogen was higher in Melbourne (mu = 48% during baseflows and 49% during storms) than in the international literature (mu = 29%). Limitations in the international dataset precluded comparison of total dissolved nitrogen. The results have implications for stormwater management. Whilst nitrogen species concentrations are variable, they are not strongly related to flow conditions, so treatment systems must be designed to cope with stochastic inflow concentrations at all times. To optimise their performance, stormwater treatments should be designed to improve dissolved nitrogen removal. Further research is needed to improve the ability of treatment systems to achieve this aim.

Cities↗
PubMed1991

Impact of dietary cereal on nutrient absorption and fecal nitrogen loss in formula-fed infants.

STUDY OBJECTIVE: To determine the capacity of infants to digest and absorb rice cereal and to determine the effect of cereal feeding on total energy and nitrogen absorption. SETTING: Subject's residences and the Texas Children's Hospital Clinical Research Center, Houston. PATIENTS: Eight healthy 1-month-old bottle-fed infants. INTERVENTIONS: Infants were fed their usual formula for 3 days. For the subsequent 6 days, they received 4 gm of rice cereal, labeled with carbon 13, per 30 ml of the formula. MEASUREMENTS AND MAIN RESULTS: Fecal balance studies were performed for a 72-hour period while the infants received only formula and again during the last 3 days of cereal feeding. Breath samples for hydrogen measurement were collected before and after the cereal feeding. Nutrient intake was measured and stools were analyzed for 13C abundance, energy, nitrogen, fiber content, and bacterial mass. Cereal absorption was 88 +/- 9% (mean +/- SD). Despite a significant increase in energy and nitrogen intake from cereal feeding, the coefficient of absorption fell (energy: 97% to 90%, p = 0.048; nitrogen: 94% to 74%, p = 0.009). Fecal dry weight increased after the cereal feeding (p = 0.004), primarily as a result of a sevenfold increase in fecal bacterial mass (p = 0.002). Fecal nitrogen increased primarily because of incorporation of nitrogen into bacteria. No differences were detected in breath hydrogen as a consequence of formula feeding versus formula-cereal feeding. CONCLUSIONS: Although cereal was relatively well-absorbed in this group of infants and increased their intakes of energy and nitrogen, it did not increase the coefficients of energy and nitrogen absorption. Cereal feeding increased fecal bacterial mass and bacterial nitrogen.

Bacteria↗
PubMed2005

Analysis of nitrogen fractions in silage by near-infrared spectroscopy.

Total nitrogen, soluble nitrogen (SN), nonprotein nitrogen (NPN), and acid-detergent insoluble nitrogen (ADIN) were analyzed in grass silage by near-infrared (NIR) spectroscopy. A set of 144 samples was used to calibrate the instrument by modified partial least-squares regression, and the following statistical results were achieved: standard error of calibration (SEC) = 0.449 and square correlation coefficient (R (2)) = 0.98 for total nitrogen x 6.25, SEC = 0.425 and R (2) = 0.95 for SN x 6.25, SEC = 0.414 and R (2) = 0.94 for NPN x 6.25, and SEC = 0.139 and R (2) = 0.84 for ADIN x 6.25. To validate the calibration performed, a set of 48 silage samples was used. Standard errors of prediction were 0.76, 0.64, 0.63, and 0.25 for total nitrogen, SN, NPN, and ADIN (all of them multiplied by 6.25), respectively, and R (2) for the regression of measurements by reference method versus NIR analysis were 0.94, 0.92, 0.90, and 0.48 for total nitrogen, SN, NPN, and ADIN, respectively. To compare the results obtained by NIR spectroscopy with those obtained by the reference methods for total nitrogen, SN, and NPN of the validation set, linear regression and paired t tests were applied, and the results were not significantly different (p = 0.05). When mean square prediction error analysis was applied, it could be concluded that for total nitrogen, SN, and NPN, a robust calibration model was obtained and that the main error was unexplained error. Statistical data for ADIN were worse than those of the other parameters; as a result NIR spectroscopy is not an effective method for quantitative analyses of ADIN in silage; nevertheless, it may be an acceptable method for semiquantitative evaluation.

Calibration↗