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Plant species richness has declined and composition shifted in response to elevated atmospheric deposition of biologically active nitrogen over much of the industrialized world. Litter thickness, litter nitrogen (N) content, and soil N mineralization rates often remain elevated long after inputs cease, clouding the prospects that plant community diversity and composition would recover should N inputs be reduced. Here we determined how N cycling, litter accumulation, and recruitment limitation influenced community recovery following cessation of long-term N inputs to prairie-like grasslands. We alleviated each of these potential inhibitors through a two-year full-factorial experiment involving organic carbon addition, litter removal, and seed addition. Seed addition had the largest effect on increasing seedling and species numbers and may be necessary to overcome long-term burial of seeds of target perennial grassland species. Litter removal increased light availability and bare sites for colonization, though it had little effect on reducing the biomass of competing neighbors or altering extractable soil N. Nonetheless, these positive influences were enough to lead to small increases in species richness within one year. We found that, although C addition quickly altered many factors assumed favorable for the target community (decreased N availability and biomass of nearby competitors, increased light and site availability), these changes were insufficient to positively impact species richness or seedling numbers over the experimental duration. However, only carbon addition had species-specific effects on the existing plant community, suggesting that its apparent limited utility may be more a result of slow recovery under ambient recruitment rather than from a lack of a restorative effect. There were dramatic interactions among treatments, with the positive effects of litter removal largely negated by carbon addition, and the positive effects of seed addition generally amplified by litter removal. It remains unclear whether each mechanism explored here will induce community recovery, but over different temporal scales. Long-term monitoring will help resolve these remaining questions. Regardless, our results suggest that reversal of species loss and compositional shifts from N deposition in prairies may be more inhibited by habitat fragmentation, recruitment limitation, and long-term suppression of fire than from continued effects of elevated N. Key words: carbon addition; diversity; grassland; invasion; litter inhibition, nitrogen deposition; prairie restoration; recovery; recruitment limitation.

In order to better understand the nitrogen (N) cycle, a pulse of [sup.15]N[O.sub.3] was applied in 1998 to a sugar maple (Acer saccharum) dominated northern hardwood forest receiving long-term (1994-2008) simulated atmospheric N deposition. Sugar maple leaf litter and live fine-root [sup.15]N were quantified for four years prior to labeling and for 11 subsequent years. Continuous sampling of [sup.15]N following addition of the tracer enabled calculation of leaf litter and fine-root N pool turnover utilizing an exponential decay function. Fine-root [sup.15]N recovery peaked at 3.7% [+ or -] 1.7% the year the tracer was applied, while leaf litter [sup.15]N recovery peaked in the two years following tracer application at ~8%. These results suggest shoots are primarily constructed from N taken up in previous years, while fine roots are constructed from new N. The residence time of N was 6.5 years in leaf litter and 3.1 years in fine roots. The longer residence time and higher recovery rate are evidence that leaves were a stronger sink for labeled N than fine roots, but the relatively short residence time of tracer N in both pools suggests that there is not tight intra-ecosystem cycling of N in this mature forest. Key words: Acer saccharum; experimental N[O.sub.3.sup.-] deposition; fine roots; leaf litter; long-term tracer experiments; nitrogen cycling; nitrogen sinks; northern hardwood: sugar maple.

Ruminants are very capable of adapting their N homeostasis to a reduced dietary N intake. However, the limits of this physiological adaptation are still unknown. The aim of the present study was to determine the quantity of dietary N intake at which the needs of the animal are still satisfied. A study was performed in young White Saanen goats under conditions of dietary N reduction. Different semisynthetic diets with 19 to 7% CP were fed. Urea transport rates across the rumen epithelium from the blood into the ruminal fluid were quantified by Ussing chamber experiments. Reduced N intake increased urea transport rates across the mucosa, which could be inhibited by phloretin. The role of parietal urease in driving urea transfer across the epithelium was negligible because its activity was inhibited by antibiotics during in vitro incubations of the epithelium. Concentrations of ammonia in the ruminal fluid were decreased by reducing dietary N intake, accompanied by diminished urease activity at the smallest dietary N intake. Over the range of plasma urea concentrations observed in the different feeding groups, salivary urea concentrations were 73% of plasma urea concentrations. By plotting plasma urea concentrations against serosal to mucosal urea flux rates, a threshold at 1.75 mmol of urea/L of plasma could be assessed, below which urea flux was strongly increased. This indicates that rumen urea transfer could be stimulated by decreased plasma urea concentrations via unknown mechanisms. The physiological relevance of this adaptation of the rumen epithelium is that it is considered a central mechanism in the N homeostasis of growing goats under reduced N intake. Key words: dietary nitrogen, goat, rumen epithelium, urea transport, Ussing chamber doi: 10.2527/jas.2010-2949

We studied the effects of supplementing N as distillers dried grains with solubles (DDGS) or urea to steers consuming corn-based diets. Six ruminally and duodenally cannulated steers (244 kg) were used in 2 concurrent 3 x 3 Latin squares and fed 1 of 3 corn-based diets: control (10.2% CP), urea (13.3% CP), or DDGS (14.9% CP). Periods were 14 d, with 9 d for adaptation and 5 d for collection of urine and feces. Urinary [sup.15]N[sup.15]N-urea enrichments, resulting from venous infusions of [sup.15]N[sup.15]N-urea, were used to measure urea kinetics. Dry matter intake (6.0 kg/d) was not affected by treatment, but N intake differed (99, 151, and 123 g/d for the control, DDGS, and urea treatments, respectively). Urea-N synthesis tended to be greater (P = 0.09) for DDGS (118 g/d) than for the control treatment (52 g/d), with the urea treatment (86 g/d) being intermediate. Urea-N excreted in the urine was greater (P < 0.03) for the DDGS (35 g/d) and urea treatments (29 g/d) than for the control treatment (13 g/d). Gastrointestinal entry of urea-N was not statistically different among treatments (P = 0.25), but was numerically greatest for DDGS (83 g/d), intermediate for urea (57 g/d), and least for the control (39 g/d). The amount of urea-N returned to the ornithine cycle tended to be greater (P = 0.09) for the DDGS treatment (47 g/d) than for the urea (27 g/d) or control treatment (16 g/d). The fraction of recycled urea-N that was apparently used for anabolism tended (P = 0.14) to be greater for the control treatment (0.56) than for the DDGS treatment (0.31), with the urea treatment (0.45) being intermediate, but no differences were observed among treatments in the amount of urea-N used for anabolism (P = 0.66). Urea kinetics in cattle fed grain-based diets were largely related to the amount of N consumed. The percentage of urea production that was captured by ruminal bacteria was greater (P < 0.03) for the control treatment (42%) than for the DDGS (25%) or urea treatment (22%), but the percentage of duodenal microbial N flow that was derived from recycled urea-N tended (P = 0.10) to be greater for the DDGS treatment (35%) than for the urea (22%) or control treatment (17%). Thus, ruminal microbes were more dependent on N recycling when the protein supplement was largely resistant to ruminal degradation. Key words: cattle, distillers dried grains with solubles, nitrogen, urea recycling doi: 10.2527/jas.2009-2641

In a developmental strategy designed to efficiently exploit and colonize sparse oligotrophic environments, Caulobacter crescentus cells divide asymmetrically, yielding a motile swarmer cell and a sessile stalked cell. After a relatively fixed time period under typical culture conditions, the swarmer cell differentiates into a replicative stalked cell. Since differentiation into the stalked cell type is irreversible, it is likely that environmental factors such as the availability of essential nutrients would influence the timing of the decision to abandon motility and adopt a sessile lifestyle. We measured two different parameters in nutrient-limited chemostat cultures, biomass concentration and the ratio of nonstalked to stalked cells, over a range of flow rates and found that nitrogen limitation significantly extended the swarmer cell life span. The transcriptional profiling experiments described here generate the first comprehensive picture of the global regulatory strategies used by an oligotroph when confronted with an environment where key macronutrients are sparse. The pattern of regulated gene expression in nitrogen- and carbon-limited cells shares some features in common with most copiotrophic organisms, but critical differences suggest that Caulobacter, and perhaps other oligotrophs, have evolved regulatory strategies to deal distinctly with their natural environments. We hypothesize that nitrogen limitation extends the swarmer cell lifetime by delaying the onset of a sequence of differentiation events, which when initiated by the correct combination of external environmental cues, sets the swarmer cell on a path to differentiate into a stalked cell within a fixed time period. doi: 10.1128/JB.01240-09

Pseudomonasputida KT2440 is a model strain for studying bacterial biodegradation processes. However, very little is known about nitrogen regulation in this strain. Here, we show that the nitrogen regulatory NtrC proteins from P. putida and Escherichia coli are functionally equivalent and that substitutions leading to partially active forms of enterobacterial NtrC provoke the same phenotypes in P. putida NtrC. P. putida has only a single [P.sub.II]-like protein, encoded by glnK, whose expression is nitrogen regulated. Two contiguous NtrC binding sites located upstream of the [[sigma].sup.N]-dependent glnK promoter have been identified by footprinting analysis. In vitro experiments with purified proteins demonstrated that glnK transcription was directly activated by NtrC and that open complex formation at this promoter required integration host factor. Transcription of genes orthologous to enterobacterial codB, dppA, and ureD genes, whose transcription is dependent on [[sigma].sup.70] and which are activated by Nac in E. coli, has also been analyzed for P. putida. Whereas dppA does not appear to be regulated by nitrogen via NtrC, the codB and ureD genes have [[sigma].sup.N]-dependent promoters and their nitrogen regulation was exerted directly by NtrC, thus avoiding the need for Nac, which is missing in this bacterial species. Based upon these results, we propose a simplified nitrogen regulatory network in P. putida (compared to that in enterobacteria), which involves an indirect-feedback autoregulation of glnK using NtrC as an intermediary. doi: 10.1128/JB.00744-09

Nitrogen is quantitatively the most important nutrient that plants acquire from the soil. It is well established that plant roots take up nitrogen compounds of low molecular mass, including ammonium, nitrate, and amino acids. However, in the soil of natural ecosystems, nitrogen occurs predominantly as proteins. This complex organic form of nitrogen is considered to be not directly available to plants. We examined the long-held view that plants depend on specialized symbioses with fungi (mycorrhizas) to access soil protein and studied the woody heathland plant Hakea actites and the herbaceous model plant Arabidopsis thaliana, which do not form mycorrhizas. We show that both species can use protein as a nitrogen source for growth without assistance from other organisms. We identified two mechanisms by which roots access protein. Roots exude proteolytic enzymes that digest protein at the root surface and possibly in the apopiast of the root cortex. Intact protein also was taken up into root cells most likely via endocytosis. These findings change our view of the spectrum of nitrogen sources that plants can access and challenge the current paradigm that plants rely on microbes and soil fauna for the breakdown of organic matter. nitrogen uptake | organic nitrogen | plant nutrition | plant roots | soil protein

Oligopeptides internalized by oligopeptide permease (Opp) transporters play key roles in bacterial nutrition, signaling, and virulence. To date, two opp operons, opp-1 and opp-2, have been identified in Staphylococcus aureus. Systematic in silico analysis of 11 different S. aureus genomes revealed the existence of two new opp operons, opp-3 and opp-4, plus an opp-5A gene encoding a putative peptide-binding protein. With the exception of opp-4, the opp operons were present in all S. aureus strains. Within a single strain, the different opp operons displayed little sequence similarity and distinct genetic organization. Transcriptional studies showed that opp-1, opp-2, opp-3, and opp-4 operons were polycistronic and that opp-5A is monocistronic. We designed a minimal chemically defined medium for S. aureus RN6390 and showed that all opp genes were expressed but at different levels. Where tested, OppA protein production paralleled transcriptional profiles, opp-3, which encodes proteins most similar to known peptide transport proteins, displayed the highest expression level and was the only transporter to be regulated by specific amino acids, tyrosine and phenylalanine. Defined deletion mutants in one or several peptide permeases were constructed and tested for their capacity to grow in peptide-containing medium. Among the four putative Opp systems, Opp-3 was the only system able to provide oligopeptides for growth, ranging in length from 3 to 8 amino acids. Dipeptides were imported exclusively by DtpT, a proton-driven di- and tripeptide permease. These data provide a first complete inventory of the peptide transport systems opp and dtpT of S. aureus. Among them, the newly identified Opp-3 appears to be the main Opp system supplying the cell with peptides as nutritional sources.

The factors controlling spatial and temporal patterns in soil solution and streamwater chemistry are highly uncertain in northern hardwood forest ecosystems in the northeastern United States, where concentrations of reactive nitrogen (Nr) in streams have surprisingly declined over recent decades in the face of persistent high rates of atmospheric Nr deposition and aging forests. Reactive nitrogen includes inorganic species (e.g., ammonium [N[H.sub.4.sup.+]], nitrate [N[O.sub.3.sup.-]]) and some organic forms (e.g., amino acids) available to support the growth of plants and microbes. The objective of this study was to examine controls on the spatial and temporal patterns in the concentrations and fluxes of nitrogen (N) species and dissolved organic carbon (DOC) in a 12-year record of soil solutions and streamwater along an elevational gradient (540-800 m) of a forested watershed at the Hubbard Brook Experimental Forest (HBEF) in the White Mountains of New Hampshire, USA. Dissolved organic N and DOC concentrations were elevated in the high-elevation spruce--fir--white birch (SFB) zone of the watershed, while N[O.sub.3.sup.-] was the dominant N species in the lower elevation hardwood portion of the watershed. Within the soil profile, N retention was centered in the mineral horizon, and significant amounts of N were retained between the lower mineral soil and the stream, supporting the idea that near- and in-stream processes are significant sinks for N at the HBEF. Temporal analysis suggested that hydrologic flow paths can override both abiotic and biotic retention mechanisms (i.e., during the non-growing season when most hydrologic export occurs, or during years with high rainfall), there appears to be direct flushing of N from the organic horizons into the stream via horizontal flow. Significant correlations between soil N[O.sub.3.sup.-] concentrations, nitrification rates and streamwater N[O.sub.3.sup.-] exports show the importance of biological production as a regulator of inorganic N export. The lack of internal production response (e.g., mineralization, nitrification) to a severe ice storm in 1998 reinforces the idea that plant uptake is the dominant regulator of export response to disturbance. Key words: dissolved organic carbon; dissolved organic nitrogen; Hubbard Brook Experimental Forest; nitrate; nitrogen; soil solution; streamwater.

A cross-ecosystem comparison of data obtained from 92 coastal zone ecosystems worldwide revealed a strong positive response of marine phytoplankton biomass to nutrient enrichment that is highly consistent with the general patterns reported previously in the limnological literature for freshwater lakes and reservoirs. Average concentrations of chlorophyll a in estuarine and coastal marine systems were strongly dependent on the mean concentrations of total nitrogen and total phosphorus in the water column. Moreover, as is true of freshwater ecosystems, the identity of the primary growth-limiting nutrient for marine phytoplankton appeared to be generally predictable from water-column total nitrogen : total phosphorus (TN : TP) ratios. This similarity in physiological response to nutrients likely derives from the shared evolutionary histories of marine and freshwater phytoplankton.

To investigate effects of green-leaf nutrient status on senesced-leaf nutrient concentrations and resorption efficiency, we developed a database of nitrogen (N) and phosphorus (P) concentrations in green and senesced leaves from 92 published studies. We fit power functions (i.e., [[nutrient].sub.sen] = A [[nutrient].sup.B.sub.gr] separately for N and P. The database encompassed 297 perennial species of different life-forms. Across these divergent species and conditions, a major control on senesced-leaf nutrient concentration was green-leaf nutrient status; nutrient concentrations in senesced leaves were positively associated with green-leaf nutrient concentrations ([r.sup.2] values from 51% to 84%). Within-species variation as well as species differences contributed to the overall variation in nutrient concentrations. Moreover, N and P resorption efficiency decreased, respectively, with increased N and P green-leaf status; fitted power functions indicated that a disproportionate amount of nutrient remained in senesced leaves of higher green-leaf nutrient status. Functional relationships between nutrient concentrations in senesced and green leaves were indistinguishable for evergreen and deciduous species, but evergreens tended to have lower concentrations in both senesced and green leaves. General relationships (across species and environments) between senesced- and green-leaf nutrient concentrations and broad, intraspecific variation in nutrient concentrations suggest that variation in resorption efficiency and proficiency could be a result (and not necessarily a cause) of species sorting across fertility gradients. Key words: deciduous vs. evergreen; fertility, gradients; global data sets; nutrient use efficiency; perennial plants; proficiency; resorption; retranslocation; senesced vs. green leaves.

In many oceanic regions, growth of phytoplankton is nitrogen-limited because fixation of [N.sub.2] cannot make up for the removal of fixed inorganic nitrogen (N[H.sup.+.sub.4], N[O.sup.-.sub.2], and N[O.sup.-.sub.3]) by anaerobic microbial processes. Globally, 30-50% of the total nitrogen loss occurs in oxygen-minimum zones (OMZs) and is commonly attributed to denitrification (reduction of nitrate to [N.sub.2] by heterotrophic bacteria). Here, we show that instead, the anammox process (the anaerobic oxidation of ammonium by nitrite to yield [N.sub.2]) is mainly responsible for nitrogen loss in the OMZ waters of one of the most productive regions of the world ocean, the Benguela upwelling system. Our in situ experiments indicate that nitrate is not directly converted to [N.sub.2] by heterotrophic denitrification in the suboxic zone. In the Benguela system, nutrient profiles, anammox rates, abundances of anammox cells, and specific biomarker lipids indicate that anammox bacteria are responsible for massive losses of fixed nitrogen. We have identified and directly linked anammox bacteria to the removal of fixed inorganic nitrogen in the OMZ waters of an open-ocean setting. We hypothesize that anammox could also be responsible for substantial nitrogen loss from other OMZ waters of the ocean. anammox | denitrification | oceanic nitrogen cycle | oxygen-minimum zone

Annual spring burning of tallgrass prairie increases plant biomass production despite losses of N and lower net N mineralization. To better understand how burning influences the cycling of N in prairie, [sup.15]N was injected to soil as [NH.sub.4.sup.+], and the partitioning between plant and soil N pools was followed over five growing seasons in annually burned and unburned prairie. Applied [sup.15]N was rapidly immobilized with < 2% and 11% of the [sup.15]N remaining in inorganic forms six days after application in burned and unburned prairie, respectively. Seventy-seven percent (burned prairie) and 70% (unburned prairie) of the applied [sup.15]N was initially recovered as soil organic N (oN), with a majority accounted for in microbial biomass. Plants contained ~20% of the applied N with the largest portion recovered from roots regardless of burning. At the end of the first growing season, only 55% of the applied [sup.15]N was recovered from the unburned prairie, while 85% was recovered from burned prairie. The total [sup.15]N content of the plants changed little during the first growing season, but the portion recovered in the rhizomes increased, indicating belowground N storage. Total recovery and distribution of applied N changed little from the end of the first to the end of the second season growing season. Accumulations of [sup.15]N within the plants decreased greatly between the second and fifth growing seasons, but N lost from plants was accounted for in oN. Conservation of N by plants and tight cycling of N within the root zone suggest mechanisms by which prairie can be a highly productive ecosystem despite limited N availability. The immobilization of potentially mineralized N within the root zone increased with burning, offsetting the loss of N to fire probably by reducing leaching and denitrification losses. Key words: competition for nitrogen, Konza Prairie Research Natural Area; Long-Term Ecological Research (LTER); microbial N demand; N cycling: N immobilization: [sup.15]N; plant--microbe interactions; tallgrass prairie.

In this study, a suspended growth sequencing batch reactor (SBR) and an attached cum suspended growth SBR were used to investigate the performance characteristics of nitrogen and phosphorus (NP) removal from municipal sewage. The effects of three controlling factors, namely batch loading rate, feed pattern (initial feed or step feed), and mixing/aeration ratio, on NP removal were investigated under nine different experimental conditions. Owing to a large number of possible combinations among the controlling factors and different experimental conditions, it is very difficult to enumerate all the available combinations experimentally. In view of this, the Taguchi method, a cost-effective technique for design of experiments, was exploited for estimating the optimal operating condition. This study also evaluated the difference between the suspended growth SBR and the attached cum suspended growth SBR. The total nitrogen (TN), total phosphorus (TP), total biochemical oxygen demand [(TBOD).sub.5], and suspended solids (SS) removal efficiencies were 90.2, 83.9, 98.6, and 93.0%, respectively, for the suspended growth SBR. The corresponding values for the attached cum suspended growth SBR were 92.6, 82.1, 98.3, and 93.1%, respectively. It was observed that the batch loading rate influenced the efficiencies in terms of TN removal. It was also noted that step feed and mixing/aeration ratio had significant impact on TP removal performance. The optimal operating condition for the suspended growth SBR system in terms of batch loading rate, feed pattern, and mixing/aeration ratio were 0.170 mgBO[D.sub.5]/mgMLVSS*d, initial feed, and 1-to-l, respectively. The associated TN, TP, TBO[D.sub.5], and SS removal efficiencies for the suspended growth SBR were 93.8, 98.2, 99.6, and 98.5%, respectively. The corresponding results for the attached cum suspended growth SBR system were 0.170 mgBO[D.sub.5]/mgMLVSS*d, initial feed, and 3-to-l, respectively. Similarly, the corresponding removal efficiencies for the attached cum suspended growth SBR were 94.7, 97.8, 99.3, and 98.8%, respectively. CE Database subject headings: Sewage; Municipal engineering; Sequencing batch reactor; Nitrogen; Phosphorus; Waste treatment.

The objectives of this study were to evaluate the potential for using blood urea N concentration to predict urinary N excretion rate, and to develop a mathematical model to estimate important variables of N utilization for several different species of farm animals and for rats. Treatment means (n = 251) from 41 research publications were used to develop mathematical relationships. There was a strong linear relationship between blood urea N concentration (mg/100 mL) and rate of N excretion (g*[d.sup.-1]*kg [BW.sup.-1]) for all animal species investigated. The N clearance rate of the kidney (L of blood cleared of urea*[d.sup.-1]*kg [BW.sup.-1]) was greater for pigs and rats than for herbivores (cattle, sheep, goats, horses). A model was developed to estimate parameters of N utilization. Driving variables for the model included blood urea N concentration (mg/100 mL), BW (kg), milk production rate (kg/d), and ADG (kg/ d), and response variables included urinary N excretion rate (g/d), fecal N excretion rate (g/d), rate of N intake (g/d), and N utilization efficiency (N in milk and gain per unit of N intake). Prediction errors varied widely depending on the variable and species of animal, with most of the variation attributed to study differences. Blood urea N concentration (mg/100 mL) can be used to predict relative differences in urinary N excretion rate (g/d) for animals of a similar type and stage of production within a study, but is less reliable across animal types or studies. Blood urea N concentration (mg/100 mL) can be further integrated with estimates of N digestibility (g/g) and N retention (g/d) to predict fecal N (g/d), N intake (g/d), and N utilization efficiency (grams of N in milk and meat per gram of N intake). Target values of blood urea N concentration (mg/100 mL) can be backcalculated from required dietary N (g/ d) and expected protein digestibility. Blood urea N can be used in various animal species to quantify N utilization and excretion rates. Key Words: Blood Urea Nitrogen, Nitrogen Excretion, Nitrogen Utilization Efficiency

We used a previously developed compartmental model to assess the postprandial distribution and metabolism of dietary nitrogen (N) in the splanchnic and peripheral areas after the ingestion of a single mixed meal containing either [sup.15]N-labeled milk or soy purified protein. Although the lower whole-body retention of dietary N from soy protein was measured experimentally, the splanchnic retention of dietary N was predicted by the model not to be affected by the protein source, and its incorporation into splanchnic proteins was predicted to reach ~35% of ingested N at 8 h after both meals. However, dietary N intestinal absorption and its appearance in splanchnic free amino acids were predicted to be more rapid from soy protein and were associated with a higher deamination, concomitant with a higher efficiency of incorporation of dietary N into proteins in the splanchnic bed. In contrast, soy protein was predicted to cause a reduction in peripheral dietary N uptake, as a consequence of both similar splanchnic retention and increased oxidation compared with milk protein. In addition, protein synthesis efficiency was reduced in the peripheral area after soy protein intake, leading to dietary N incorporation in peripheral proteins that fell from 26 to 19% of ingested N 8 h after milk and soy protein ingestion, respectively. Such a model thus enables a description of the processes involved in the differential metabolic utilization of dietary proteins and constitutes a valuable tool for further definition of the notion of protein quality during the period of protein gain. KEY WORDS: * interorgan amino acid metabolism * milk protein * soy protein * postprandial period * parameter estimation H

L-5-oxoproline (OP), an intermediate of the (gamma)-glutamyl cycle of glutathione synthesis and degradation, may serve as a probe for the state of glutathione kinetics. We explored the whole-body carbon and nitrogen kinetics of OP in five male healthy subjects (75.2 kg; 181 cm; 26 y) after a 5-d adaptation to an adequate L-amino acid-based diet (160 mg N*kg(super -1)*d(super -1);188 kJ*kg(super -1)*d(super -1), using a crossover design. On day 6 of the diet period, we carried out an 8-h tracer protocol (3 h fast; 5 h fed; 2/3 of daily nitrogen intake) with intravenous infusion of L-[1-(super 13)C]oxoproline and L-[3,3-(super 2)H]cysteine or, in randomized order, on the second occasion, L-[(super 15)N]oxoproline and L-[3,3-(super 2)H]cysteine. Plasma OP was isolated by cation exchange and after addition of internal standards (DL-[(super 2)H (sub 3)]5-oxoproline; L-[(super 15)N, U-(super 13)3C(sub 5)]-5-oxoproline; DL-[(super 2)H(sub 3)]-glutamic acid) derivatized to form TBDMS esters and measured by gas chromatography/mass spectrometry. Plasma OP concentration did not differ between fed and fasted state (fast: 59.4 +/- 8.3; fed 59.2 +/- 8.9 nmol/mL). (super 13)C- and (super 15)N OP flux during the fasted and fed state were 19 +/- 3.6, 21.2 +/- 3.2, and 22.6 +/- 3.9, 25.8 +/- 4.3 (mu)mol*kg(super -1)*30 min(super -1), respectively. OP oxidation was 15.6 +/- 3.6 and 17.9 +/- 3.5 (mu)mol*kg(super -1)* 30 min(super -1), in fasting and feeding, respectively, (P < 0.05). More than 80% of the plasma flux was oxidized. These findings are compared with the published literature on GSH turnover in plasma of human subjects and underscore the need to define more completely the dynamic aspects of glutathione metabolism and of the intermediates of the (gamma)-glutamyl cycle. KEY WORDS: oxoproline kinetics; glutathione; stable isotopes; oxidation; flux; humans

The dry weight (DW), carbon (C) and nitrogen (N) components of four species of caprellid amphipods inhabiting Sargassum yezoense were examined. Collected from the Otsuchi Bay in northeastern Japan, the Caprella danilevskii, C. subinermis, C. penantis and C. verrucosa were kept in laboratory aquariums with running sea water and sorted within 24 hours after collection. Results showed that males have a greater pereonite II length, higher DW, C and N contents in all four species. Regressions of female pereonite II length in DW, C and N significantly varied from males in all four species.

Nitrogen (N) balance was determined in 36 pigs (BW 24 to 30 kg) fed diets inducing different ileal endogenous N losses (ENL). We tested the hypothesis that enhanced ENL may be indicative of a higher recycling of endogenous proteins that will induce a greater urinary N loss and a lower efficiency of the dietary N utilization for retention. The cornstarch-based diets contained either soy concentrate (SC), soybean meal (SBM), a mixture of toasted and untoasted soybean meal (mSBM), dehulled-toasted rapeseed cake (RC1), non-dehulled-toasted rapeseed cake (RC2), or dehulled-untoasted rapeseed cake (RC3). The diets were balanced for their content of apparent ileal digestible (ID) CP (108 g/kg feed) and apparent ID of Lys, Thr, Met+Cys, Trp, and Ile. Feeding level was 2.7 times ME for maintenance per kilogram [BW.sup..75] and restricted to 88% of the requirements for ID Lys as the first-limiting amino acid. During a 5-d period, urine and feces were collected daily in metabolism cages. Compared with the SC diet (low ENL), the diets with SBM (medium ENL) and mSBM (high ENL) resulted in a greater (P < .05) urinary N excretion. Nitrogen retention tended to be less (P = .08) in pigs fed diets that caused greater ENL. The utilization of ID N for retention in pigs fed the mSBM diet was lower (P < .05) than for those fed the SC diet. There were no differences in urinary N excretion, N retention, and the utilization of ID N for retention in pigs fed the rapeseed diets of different fiber contents (hulls as the NDF source). We concluded that, at similar intakes of the first-limiting ID amino acid, N retention in pigs fed soybeans tended to be reduced by greater ENL as induced by antinutritional factors (e.g., trypsin inhibitors). Rapeseed hulls, as the predominant fiber source, do not affect N retention and the utilization of ID N for retention. Key Words: Nitrogen Balance, Soybeans, Rapeseed, Pigs

We investigated the effects of various protein sources on the apparent ileal digestibilities (AID) of CP and amino acids (AA) and on the recoveries of ileal endogenous nitrogen (N) in pigs. Ileal endogenous N losses (ENL) were measured using the 15N-isotope dilution method. Thirteen pigs (BW of 13 to 20 kg) were fitted with a post-valve-T-cecal cannula and two indwelling blood catheters. They were fed twice daily at a level of 2.6 times ME for maintenance. Cornstarch-based diets contained a soy concentrate (SC; 180.5 g/kg), soybean meal (SBM; 295 g/kg), or a mixture of toasted and untoasted soybean meal (mSBM; 330.4 g/kg) in Trial I or three rapeseed cakes, dehulled-toasted (RC1; 395 g/kg), non-dehulled-toasted (RC2; 458 g/kg), and dehulled-untoasted (RC3; 390 g/kg) in Trial II. The protein sources provided diets with similar levels of apparent ileal digestible CP (108 g/kg as-fed diet) and Lys, Met+Cys, Thr, and Trp. The AID of CP was greater (P < .05) for the SC (86.8%) and SBM (82.8%) than for the SBM (68.1%) diet. In Trial II, the AID of CP wa greater (P < .05) for RCI (76.2%) and RC3 (75.8%) than for the RC2 (69.5%) diet. For all diets, the differences in the AID for most of the AA corresponded to the differences in the AID of CP. The ENL (g/kg DMI) were greater (P < .05) for the mSBM diet (3.75) than for the SC (2.53) and SBM (2.53) diets in Trial I but were similar (P > .05; 2.24, 3.03, and 2.89 for RC1, RC2, and RC3, respectively) among diets in Trial II. We concluded that AID of CP of the soybean diets were associated with endogenous and dietary N losses. For these diets, increased ENL and dietary N losses were associated with a higher dietary trypsin inhibitor activity. For the rapeseed diets, dehulling increased AID of CP and AA, due to reduced ENL (P = .08) and dietary N losses (P < .05). Toasting of dehulled rapeseed cake did not affect the AID of CP and AA (P > .05) while reducing the true ileal CP digestibility (P < .05). Key Words: Pigs, Nitrogen, Digestibility, Soybeans, Rapeseed, Feed Processing

Using 73 Large White gilts, we studied the lysine requirement during lactation. Sow and pig performance and nitrogen balance of sows were measured during the total 21-d lactation period. Variation in body composition of sows between farrowing and weaning was determined by the comparative slaughter technique. Two levels of crude protein (15.5 and 17.1%) were combined with two levels of L-lysine HCl supplementation (0 and. 16%), resulting in four diets termed P1L1, P1L2, P2L2, and P2L3, containing .66, .77, .77, and .87% crude lysine, and 15.5, 15.5, 17.1, and 17.1% crude protein, respectively. Sows' feed intake, litter growth rate, and milk energy and protein output were not affected by the diet. Nitrogen balance over the total lactation increased (P < .001) with an increase in lysine and(or) protein (-11.7, -7.0, -3.4, and .4 g N/d for P1L1, P1L2, P2L2, and P2L3 diets, respectively). The losses of body weight and muscle weight were higher in P1L1 gilts (P < .01 and .05, respectively) than in gilts on other treatments, whereas the loss of adipose tissue and backfat was similar for the four groups. Multiple linear relationships between lysine intake and milk nitrogen output as predictors and nitrogen balance (N balance = -15.8 + 1.22 lysine - .63 N milk, [R.sup.2] = .89) or variation of muscle weight (Vm = -477 + 30.1 lysine - 14.7 N milk, [R.sup.2] = .70) as predicted values were calculated to estimate lysine requirement according to production performance of sows. Calculations show that for achieving a zero protein balance, 45 to 55 g/d of crude lysine are required for normal to high-yielding sows, respectively. Key Words: Sows, Lactation, Lysine, Requirements, Protein

Byline: Aino-Maija Evers (1), Elise Ketoja (2), Margareta Hagg (3), Sirkka Plaami (3), Ulla Hakkinen (3), Raili Pessala (4) Keywords: Apium graveolens var. dulce (Miller) Pers.; celery; internal quality; irrigation; nitrogen fertilization Abstract: The effect of decreased nitrogen rates (90, 60 and 30 kg N/ha) with and without irrigation on celery yield quantity and internal quality were studied in field experiments in 1993 and 1994. The decreased nitrogen rates reduced yields in both years. In the dry and warm conditions of 1994 nitrogen x irrigation interaction was clearly observed irrigation increased yield more at higher nitrogen rates than at lower nitrogen rates. In the rainy conditions of 1993 irrigation did not effect the yield level.On the other hand, in both years, decreased nitrogen rates increased dry matter, vitamin C and dietary fiber contents, and nitrogen had a minor effect on total sugar content. In 1994 alpha- and beta carotene and thiamin were also analyzed but nitrogen had no effect on them. Irrigation increased dry matter and total sugar contents at the two lowest nitrogen rates in 1994, but decreased vitamin C contents in both years. There was also slight evidence that irrigation might decrease alpha- and beta-carotene and thiamin contents. Author Affiliation: (1) Department of Plant Production, University of Helsinki, P.O. Box 27, 00014, Finland (2) Agricultural Research Centre, Data and Information Services, 31600, Jokioinen, Finland (3) Laboratory of Food Chemistry, Agricultural Research Centre, 31600, Jokioinen, Finland (4) Agricultural Research Centre, Institute of Horticulture, 21500, Piikkio, Finland Article History: Registration Date: 30/09/2004

To study the effect of resistant starch (RS) on the route of nitrogen excretion, we fed three groups of six cannulated piglets each a diet containing either uncooked resistant starch (R[S.sub.2]), retrograded resistant starch (R[S.sub.3]) or glucose. The use of piglets with a cannula at the end of the ileum allowed measurement of the amount of nitrogen that entered the colon. Ileal digesta, urine and feces were collected quantitatively and weighed, and dry matter, starch and nitrogen content were determined. We hypothesized that R[S.sub.2] would lower colonic absorption of nitrogen when compared with R[S.sub.3], because R[S.sub.2] may be more fermentable than R[S.sub.3], thus trapping more nitrogen in bacteria. The piglets fed R[S.sub.3] had a significantly higher production of ileal digesta and feces than the piglets fed glucose or R[S.sub.2]. In the piglets fed R[S.sub.2], 44% of the amount of RS fed was recovered in the ileal digesta; in the piglets fed R[S.sub.3], 71% was recovered. Thus, more fermentable material entered the colon in the R[S.sub.3]-fed piglets than in the R[S.sub.2]-fed piglets. Virtually no starch was recovered in the feces of any dietary group. Replacement of glucose by either R[S.sub.2] or R[S.sub.3] did not affect nitrogen retention but increased fecal nitrogen excretion. Compared with glucose, R[S.sub.3] but not R[S.sub.2] reduced urinary nitrogen excretion, mainly in the form of urea, and reduced the amount of nitrogen absorbed by the colon when expressed as a percentage of the amount of nitrogen entering the colon. This study provides evidence that R[S.sub.3], but not R[S.sub.2], shifts nitrogen excretion from urine to feces in cannulated piglets. KEY WORDS: resistant starch; uncooked starch; retrograded starch; nitrogen excretion; pigs

We hypothesized that a limitation in the endogenous formation of glycine might constrain catch-up growth during recovery from severe childhood malnutrition. The urinary excretion of 5-L-oxoproline is increased when the glycine available for glutathione synthesis is limited. Urinary excretion of 5-L-oxoproline was measured throughout recovery in 12 children (aged 16 [+ or -] 6 mo) with severe malnutrition. Urinary 5-L-oxoproline was similar at admission and after recovery, but was increased significantly during rapid catchup growth. There was a significant relationship between the rate of weight gain and 5-L-oxoproline excretion in urine. In nine children (aged 15 [+ or -] 5 mo), the effect of oral supplementation with glycine, [1.7 mmol/ (kg [center dot] d) for 48 h] during rapid catch-up growth on 5-L-oxoprolinuria and blood glutathione concentration was determined. in seven of the nine children weight gain was less than 17 g/(kg [center dot] d) and following oral glycine supplements 5-L-oxoproline excretion was reduced up to 64% and blood glutathione concentration increased up to 100%. In the two children who were gaining weight at a rate >17 g/(kg [center dot] d), glycine supplementation was associated with a further increase in 5-L-oxoproline excretion and a decrease in blood glutathione. If 5-L-oxoproline is an index of the relative availability of glycine, then the data indicate that glycine may be limiting during rapid catch-up growth. This would have important implications for repletion of muscle and gain in height. INDEXING KEY WORDS: catch-upgrowth, glutathione, human protein requirements, amino acids, nitrogen

Today because of tools capable of probing the details of metabolism, we are able to study the utilization of amino acids in specific, physiologically important processes. Such information may lead to recommended dietary allowances for each amino acid specific for subpopulations and perhaps individuals. These new findings identify the metabolic end-products of some amino acids as crucial intermediates in the maintenance of a variety of physiological functions that bear no direct relationship to protein metabolism. The precursor amino acids for these intermediate compounds are either non-essential or conditionally essential and thus may play a specific, non-protein, role in amino acid requirements in individuals close to nitrogen equilibrium. Another exciting area arises from the marked dissimilarity between the amino acid composition of milk proteins and other body proteins, suggesting that some milk proteins may have evolved to serve unique functions through specific digestion products. Such products may be important in micronutrient absorption in the neonate. Thus, amino acid requirements appear to reach beyond the tradition areas of nitrogen and protein metabolism. J. Nutr. 124: 1754S-1764S, 1994. INDEXING KEY WORDS: * amino acids * protein * immune function * milk digopeptides

The effects of low nitrogen diets (oral and parenteral) on nutritional status and residual renal function were evaluated in rats with experimentally induced severe renal failure (partial nephrectomy) and compared with the effects of a normal protein diet. Non-uremic rats were used as controls. Muscle protein synthesis was significantly lower in uremic rats fed a normal protein diet than in those fed low protein diets. Values for serum insulin-like growth factor 1 (IGF-1) were significantly lower than for controls in all uremic groups as were the wet and dry weights of skeletal muscle. The glomerular filtration rate was studied after 3 wk of nutritional intervention. Serum creatinine concentration was lower and creatinine clearance greater in uremic rats given the low nitrogen dietary treatments (both oral and parenteral) compared with those fed the normal protein diet. However, the glomerular filtration rate determined with 51Cr-EDTA clearance did not differ between uremic rats with normal and low protein intake. Thus, a low nitrogen diet had positive effects on uremic toxicity and did not compromise nutritional status. The results do not, however, establish a favorable influence on residual renal function and emphasize the need for reliable methods for studying dietary effects on renal function in uremia.

Arctic-nesting female Ross' Geese tissues were examined prior to and after fasting during egg laying and incubation to determine the validity of the hypothesis that sigma15N values increase in bird tissues as a result of nutritional stress. Results revealed substantial reductions in body, pectoral muscle, liver and abdominal fat mass from arrival through incubation. Compared to geese taken prior to clutch initiation, post-incubating geese showed higher sigma15N values were observed in the pectoral muscle and liver. A tissue sigma15N enrichment mechanism resulting from lower nutrient intake was proposed.

The applicability and advantages of using fecal nitrogen (FN) as an index of dietary quality for estimating the free-ranging and captive vertebrate mammalian herbivores are discussed. Several new management and research strategies to enhance FN application are also presented.

Measurements of rates of canonical, that is, heterotrophic, water-column denitrification were performed by [super 15]N incubation techniques at a number of coastal and open ocean stations in the Arabian Sea. Nitrogen excess gas measurements were found to predict a larger nitrogen anomaly than estimated by classical stoichiometric methods.