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PubMed2001

Interactive effects of soil temperature, atmospheric carbon dioxide and soil N on root development, biomass and nutrient uptake of winter wheat during vegetative growth.

Nutrient requirements for plant growth are expected to rise in response to the predicted changes in CO(2) and temperature. In this context, little attention has been paid to the effects of soil temperature, which limits plant growth at early stages in temperate regions. A factorial growth-room experiment was conducted with winter wheat, varying soil temperature (10 degrees C and 15 degrees C), atmospheric CO(2) concentration (360 and 700 ppm), and N supply (low and high). The hypothesis was that soil temperature would modify root development, biomass allocation and nutrient uptake during vegetative growth and that its effects would interact with atmospheric CO(2) and N availability. Soil temperature effects were confirmed for most of the variables measured and 3-factor interactions were observed for root development, plant biomass components, N-use efficiency, and shoot P content. Importantly, the soil temperature effects were manifest in the absence of any change in air temperature. Changes in root development, nutrient uptake and nutrient-use efficiencies were interpreted as counterbalancing mechanisms for meeting nutrient requirements for plant growth in each situation. Most variables responded to an increase in resource availability in the order: N supply >soil temperature >CO(2).

Adaptation, Physiological↗

PubMed2005

Nitrogen metabolism in the rumen.

Protein metabolism in the rumen is the result of metabolic activity of ruminal microorganisms. The structure of the protein is a key factor in determining its susceptibility to microbial proteases and, thus, its degradability. Ruminal protein degradation is affected by pH and the predominant species of microbial population. Ruminal proteolytic activity decreases as pH decreases with high-forage dairy cattle-type rations, but not in high-concentrate beef-type rations. Accumulation of amino acid (AA) N after feeding suggests that AA uptake by rumen microorganisms could be the limiting factor of protein degradation in the rumen. In addition, there are several AA, such as Phe, Leu, and Ile, that are synthesized by rumen microorganisms with greater difficulty than other AA. The most common assessment of efficiency of microbial protein synthesis (EMPS) is determination of grams of microbial N per unit of rumen available energy, typically expressed as true organic matter or carbohydrates fermented. However, EMPS is unable to estimate the efficiency at which bacteria capture available N in the rumen. An alternative and complementary measure of microbial protein synthesis is the efficiency of N use (ENU). In contrast to EMPS, ENU is a good measurement for describing efficiency of N capture by ruminal microbes. Using EMPS and ENU, it was concluded that optimum bacterial growth in the rumen occurs when EMPS is 29 g of bacterial N/kg of fermented organic matter, and ENU is 69%, implying that bacteria would require about 1.31 x rumen-available N per unit of bacterial N. Because the distribution of N within bacterial cells changes with rate of fermentation, AA N, rather than total bacterial N should be used to express microbial protein synthesis.

Amino Acids↗

PubMed2002

Peripheral and splanchnic metabolism of dietary nitrogen are differently affected by the protein source in humans as assessed by compartmental modeling.

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 (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 approximately 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.

Amino Acids↗

PubMed2001

Nitrogen and phosphorus variation in shallow groundwater and assimilation in plants in complex riparian buffer zones.

The study of purification efficiency and nutrient assimilation in plants was made in two riparian buffer zones with a complex of wet meadow and grey alder (Alnus incana) stand. In the less polluted Porijõgi test site, the 31 m wide buffer zone removed 40% of total nitrogen (total-N) and 78% of total phosphorus (total-P), while a heavily polluted 51 m wide buffer zone in Viiratsi retained 85% of total-N and 84% of total-P. The input of nutrients and purification efficiency displayed a significant relationship. The total-N removal in buffer zone was negative when the input value was less than 0.3 mg l(-1) and the purification efficiency was always positive when the input value exceeded 5 mg l(-1). The purification efficiency of total-P was positive when the input value exceeded 0.15 mg l(-1). Grass vegetation plays an important role in nutrient retention in riparian buffer strips. The maximum phytomass production was measured in Porijõgi site where production of the Filipendula ulmaria community was up to 2,358 g m(-2), assimilation of N 32.1 and of P 4.9 g m(-2), respectively. This is much higher than the biomass production and N and P uptake of the grey alders (Alnus incana) at the same site--1,730, 20.5 and 1.5 g m(-2), respectively.

Biomass↗

PubMed2004

Four permeases import proline and the toxic proline analogue azetidine-2-carboxylate into yeast.

We have found that proline and the toxic proline analogue azetidine-2-carboxylate (AzC) are efficiently imported into Saccharomyces cerevisiae cells by four amino acid permeases, including two nitrogen-regulated permeases (PUT4 and GAP1) and two permeases that are regulated by the SPS sensor of extracellular amino acids (AGP1 and GNP1). In contrast to Agp1p, Gnp1p is not functionally expressed when cells are grown on media containing proline as sole nitrogen source. These findings have implications for the interpretation of studies using AzC to characterize nitrogen source-dependent regulation of amino acid uptake and of post-Golgi targeting and localization of amino acid permeases in yeast.

Amino Acid Transport Systems, Acidic↗

PubMed2005

Long-term aeration management for improved N-removal via SND in a sequencing batch reactor.

Management of the aeration length in a sequencing batch reactor (SBR) can improve N-removal by minimising the amount of organic substrate that is oxidised aerobically. This study investigates the long-term effect of aeration control on N-removal via simultaneous nitrification and denitrification (SND) by a mixed culture in a 2L acetate-fed SBR, using PHB as the electron donor for denitrification. The reactor was operated continuously with automated termination of the aerobic phase after ammonium depletion, using the specific oxygen uptake rate (SOUR) as the control parameter. This resulted in an increase of the organic loading rate (OLR) from 0.33 to 0.59 g BOD g(-1)d(-1). Over the first 12 cycles of operation, the PHB content of the biomass increased three-fold and resulted in a progressively increasing SOUR, which allowed an increased amount of nitrogen removal via SND from 34% to 52%. After one month of continuous operation with controlled aeration, the settling efficiency of the biomass had significantly improved (SVI 70 mL g(-1) X). Long-term oxygen management resulted in biomass with a higher capacity for N-removal via SND and improved settling characteristics. Our results may help to explain long-term historical effects of N-removal capabilities in WWTPs and assist design engineers in choosing an appropriate aeration length and OLR.

Aerobiosis↗

PubMed2005

Signal transduction protein PII phosphatase PphA is required for light-dependent control of nitrate utilization in synechocystis sp. strain PCC 6803.

Signal transduction protein P(II) is dephosphorylated in Synechocystis sp. strain PCC 6803 by protein phosphatase PphA. To determine the impact of PphA-mediated P(II) dephosphorylation on physiology, the phenotype of a PphA-deficient mutant was analyzed. Mutants lacking either PphA or P(II) were impaired in efficient utilization of nitrate as the nitrogen source. Under conditions of limiting photosystem I (PSI)-reduced ferredoxin, excess reduction of nitrate along with impaired reduction of nitrite occurred in P(II) signaling mutants, resulting in excretion of nitrite to the medium. This effect could be reversed by increasing the level of PSI-reduced ferredoxin. We present evidence that nonphosphorylated P(II) controls the utilization of nitrate in response to low light intensity by tuning down nitrate uptake to meet the actual reduction capacity. This control mechanism can be bypassed by exposing cells to excess levels of nitrate. Uncontrolled nitrate uptake leads to light-dependent nitrite excretion even in wild-type cells, confirming that nitrate uptake controls nitrate utilization in response to limiting photon flux densities.

Light↗

PubMed1985

Tomato responses to ammonium and nitrate nutrition under controlled root-zone pH.

Tomato (Lycopersicon esculentum L. Mill. 'Vendor') plants were grown for 21 days in flowing solution culture with N supplied as either 1.0 mM NO3- or 1.0 mM NH4+. Acidity in the solutions was automatically maintained at pH 6.0. Accumulation and distribution of dry matter and total N and net photosynthetic rate were not affected by source of N. Thus, when rhizosphere acidity was controlled at pH 6.0 during uptake, either NO3- or NH4+ can be used efficiently by tomato. Uptake of K+ and Ca2+ were not altered by N source, but uptake of Mg2+ was reduced in NH4(+)-fed plants. This indicates that uptake of Mg2+ was regulated at least partially by ionic balance within the plant.

Biomass↗

PubMed2005

Nitrogen and phosphorus removal from plant nursery runoff in vegetated and unvegetated subsurface flow wetlands.

Subsurface horizontal flow reed beds are being evaluated for Nitrogen (N) and Phosphorus (P) removal from plant nursery runoff water in New South Wales Australia. The need to include plants (Phragmites australis), the effect of reaction time (3.5 v 7.0 d) and dissolved organic carbon (DOC) on N and P removal in batch fed gravel wetland tubs (55 L) was studied over 19 months. Simulated nursery runoff water containing N (10.1 mg L(-1), 74% as NO3) and P (0.58 mg L(-1), 88% as PO4) and DOC (2-5 mg L(-1)) was used. The planted wetland tubs removed >96% TN and TP over most of the 19-month study period while unplanted tubs were inefficient (<16% N and <45% P removal) and occasionally discharged nutrients. Doubling the reaction time to 7.0 days had no effect on nutrient removal. Plant nutrient uptake accounted for most of the N (76%) and P (86%) removed while roots and rhizomes were the dominant sink (N 58%, P 67%). The addition of methanol (C:N-3:1) to unplanted tubs achieved 81-98% N removal. In Carbon limited low nutrient nursery runoff, plants were essential to a gravel-based wetland to achieve efficient nutrient removal with effluent TN and TP concentrations of <1 mg L(-1) and 0.05 mg L(-1), respectively with a 3.5 day reaction time.

Agriculture↗

PubMed2006

Effects of the internal recycling rate on biological nutrient removal and microbial community structure in a sequential anoxic/anaerobic membrane bioreactor.

This study investigated the effects of the internal recycling rate on nutrients removal in a sequential anoxic/anaerobic membrane bioreactor (SAM). Microbial community structure in sludge from the SAM was studied using quinone profile method. Above 98% COD, 68% nitrogen, and 55% phosphorus removal efficiencies were achieved when the internal recycling rate was 2.5 times influent flow. At that rate, the optimum specific nitrate loading rate and COD/NO(3)-N ratio were found to be 2.24 mgNO(3)-N g(-1) MLSS h(-1) and 9.13, respectively. Batch tests demonstrated that anoxic condition suppressed phosphorus release, and that denitrification was also influenced by initial substrate concentration. Denitrification appeared to have some priority over phosphorus release for substrate uptake. Microbial community analysis revealed a predominance of the subclass beta-Proteobacteria. Furthermore, it was found that Rhodocyclus-related bacteria were efficient at phosphorus removal than Actinobacteria.

Aerobiosis↗

PubMed2004

Agronomic and environmental impacts of a single application of heat-dried sludge on an Alfisol.

A field experiment was conducted on Alfisols in South-West France to assess the agronomic and environmental impacts of a single application of heat-dried sludge pellets at 11.1 Mg dry matter ha-1. The sludge pellets, with a moisture level of 9.5%, were spread on an irrigated crop of maize (Zea mays L.). This treatment was compared with inorganic fertilization (urea and diammonium phosphate mixed with KCl). Soil properties, yield and the composition of maize and the quality of drained water were monitored over 1 year to detect any changes resulting from sludge application. Amongst several determined soil properties, only two were significantly modified by the sludge application: The nitric nitrogen stock of the soil was higher in the inorganic fertilized plot, whereas Olsen-P soil content was higher in the sludge-amended plot. Agronomic recovery rates of N and P added by sludge were high: For the first crop following application, total amounts of N and P supplied by the sludge had the same efficiency as approximately 45% of the N and P amounts supplied by inorganic fertilizer. This ratio was 7% for the N uptake by the second maize crop. The quality and quantity of maize were equally good with both types of fertilization. During the 2 years following sludge spreading, N leaching remained as low in the sludged plot as in the inorganically fertilized one. The Cu, Zn, Cr, Cd, Pb and Ni composition of the drainage water was affected by neither of the types of amendment. From the heavy-metal contents of the soil, water and maize monitored over 1 year in the field experiment and from literature data for cow manure and atmospheric emissions, a theoretical balance between crop soil heavy-metal input and output over one century was drawn up. The long-term impact of cow manure on Zn, Ni and Cr in soil is higher than that of the studied heat-dried sludge. Obviously, sludge tended to cause a strong increase in soil Cu storage, valued for these soils, which are otherwise very Cu deficient.

Crops, Agricultural↗

PubMed1996

A binding-lipoprotein-dependent oligopeptide transport system in Streptococcus gordonii essential for uptake of hexa- and heptapeptides.

Cells of the oral bacterium Streptococcus gordonii express three cytoplasmic membrane-bound lipoproteins with apparent molecular masses of 76 to 78 kDa that are the products of three genes (designated hppA, hppG, and hppH). The lipoproteins are immunologically cross-reactive, contain 60% or more identical amino acid residues, and are highly similar to the AmiA, AliA (PlpA), and AliB substrate-binding protein components of an oligopeptide permease in Streptococcus pneumoniae. Insertional inactivation of the hppA or hppH gene resulted in loss of the ability of S. gordonii cells to utilize specific peptides of five to seven amino acid residues for growth. An insertion within the COOH-terminal coding region of hppG that caused apparent truncation of the HppG polypeptide had a similar effect; however, S. gordonii mutants in which HppG polypeptide production was abolished were still able to grow on all oligopeptides tested. Inactivation of hppA gene (but not inactivation of the hppG or hppH gene) caused reduced growth rate of cells in complex medium, slowed the rate of development of competence for transformation, reduced the efficiency of transformation, and increased the resistance of cells to aminopterin. These results suggest that the formation of a solute-binding-protein complex consisting of at least the HppA and the HppH lipopolypeptides is necessary for binding and subsequent uptake of primarily hexa- or heptapeptides by a Hpp (Hexa-heptapeptide permease) system in S. gordonii. In addition, Hpp may play a role in the control of metabolic functions associated with the growth of streptococcal cells on complex nitrogen sources and with the development of competence.

Amino Acid Sequence↗

PubMed2003

Influence of an organic mulching on fertilizer nitrogen use efficiency and herb and essential oil yields in geranium (Pelargonium graveolens).

In a field study, conducted at Lucknow ( 26.5 degrees N, 80.5 degrees E and 120 m altitude), India for two years (1996-1997 and 1997-1998), eight treatment combinations of two variables of organic mulch (paddy straw at 7 t/ha and no mulch) and four levels of fertilizer nitrogen (0, 80, 160 and 240 kg/ha) were examined to observe the effect of organic mulching on N-use efficiency and essential oil yield in a multi-harvested geranium crop. Results revealed that application of paddy straw mulch increased the herb and essential oil yields in geranium by 23% and 27%, respectively, over the unmulched control at planted crop harvest. Corresponding values at regenerated crop harvest were 18.7% and 19.2%. A significant response to N was observed with 160 kgN/ha in mulched plot over the same level of N in the unmulched plot. Using paddy straw mulch, nitrogen uptake by plants of planted and regenerated crops was increased by 33% and 28.4%, respectively, over the unmulched control. Apparent N recoveries by planted and regenerated crops were estimated to be 33.7% and 22.7% for the unmulched control, as against 40% and 29.2% with paddy straw mulch at 160 kgN/ha. The quality of essential oil of geranium in terms of its major constituents, citronellol and geraniol, was not affected by the use of organic mulching and nitrogen fertilization and these constituents were found to be of a standard acceptable in international trade. It was concluded from this study that use of an organic mulch with 160 kgN/ha proved better in terms of economising 80 kgN/ha to produce an economic yield of 96.1 kg geranium oil from two harvests under subtropical conditions of the north Indian plains. At 160 kgN/ha, paddy straw mulch application permitted the geranium crop to produce 18.4 kg/ha more oil which gave an additional return of Rs. 53,600/ha than that of unmulched control. Paddy straw mulch and nitrogen fertilization had no adverse effect on the quality of essential oil of geranium.

Agriculture↗

PubMed2005

Diversity-productivity relationships: initial effects, long-term patterns, and underlying mechanisms.

A common pattern emerging from studies on the relationship between plant diversity and ecosystem functioning is that productivity increases with diversity. Most of these studies have been carried out in perennial grasslands, but many lasted only two growing seasons or reported data from a single year. Especially for perennial plant communities, however, the long-term effects of diversity are important. The question whether interactions between few species or among many species lead to increased productivity remained largely unanswered. So far, the main mechanism addressed is the increased input of nitrogen by nitrogen-fixing legumes. We report that other mechanisms can also generate strong increases of productivity with diversity. Results from 4 consecutive years of a plant diversity experiment without legumes show that a positive relationship between plant species richness and productivity emerged in the second year and strengthened with time. We show that increased nutrient use efficiency at high species richness is an important underlying mechanism. This mechanism had not been discussed in earlier studies. Furthermore, our results suggest that complementary nutrient uptake in space and time is important. Together, these mechanisms sustain consistently high productivity at high diversity.

Biodiversity↗

PubMed2004

Atg21 is a phosphoinositide binding protein required for efficient lipidation and localization of Atg8 during uptake of aminopeptidase I by selective autophagy.

Delivery of proteins and organelles to the vacuole by autophagy and the cytoplasm to vacuole targeting (Cvt) pathway involves novel rearrangements of membrane resulting in the formation of vesicles that fuse with the vacuole. The mechanism of vesicle formation and the origin of the membrane are complex issues still to be resolved. Atg18 and Atg21 are proteins essential to vesicle formation and together with Ygr223c form a novel family of phosphoinositide binding proteins that are associated with the vacuole and perivacuolar structures. Their localization requires the activity of Vps34, suggesting that phosphatidylinositol(3)phosphate may be essential for their function. The activity of Atg18 is vital for all forms of autophagy, whereas Atg21 is required for the Cvt pathway but not for nitrogen starvation-induced autophagy. The loss of Atg21 results in the absence of Atg8 from the pre-autophagosomal structure (PAS), which may be ascribed to a reduced rate of conjugation of Atg8 to phosphatidylethanolamine. A similar defect in localization of a second ubiquitin-like conjugate, Atg12-Atg5, suggests that Atg21 may be involved in the recruitment of membrane to the PAS.

Aminopeptidases↗

PubMed1995

Carbohydrate utilization patterns and substrate preferences in Bacteroides thetaiotaomicron.

Specific growth rates of Bacteroides thetaiotaomicron NCTC 10582 with either glucose, arabinose, mannose, galactose or xylose as sole carbon sources were 0.42/h, 0.10/h, 0.38/h, 0.38/h and 0.16/h respectively, suggesting that hexose metabolism was energetically more efficient than pentose fermentation in this bacterium. Batch culture experiments to determine whether carbohydrate utilization was controlled by substrate-induced regulatory mechanisms demonstrated that mannose inhibited uptake of glucose, galactose and arabinose, but had less effect on xylose. Arabinose and xylose were preferentially utilized at high dilution rates (D > 0.26/h) in carbon-limited continuous cultures grown on mixtures of arabinose, xylose, galactose and glucose. When mannose was also present, xylose was co-assimilated at all dilution rates. Under nitrogen-limited conditions, however, mannose repressed uptake of all sugars, showing that its effect on xylose utilization was strongly concentration dependent. Studies with individual D-ZU-14C]-labelled substrates showed that transport systems for glucose, galactose, xylose and mannose were inducible. Measurements to determine incorporation of these sugars into trichloroacetic acid-precipitable material indicated that glucose and mannose were the principal precursor monosaccharides. Xylose was only incorporated into intracellular macromolecules when it served as growth substrate. Phosphoenolpyruvate:phosphotransferase systems were not detected in preliminary experiments to elucidate the mechanisms of sugar uptake, and studies with inhibitors of carbohydrate transport showed no consistent pattern of inhibition with glucose, galactose, xylose and mannose. These results indicate the existence of a variety of different systems involved in sugar transport in B. thetaiotaomicron.

Journal Article↗

PubMedDate not supplied

Comparison of estimates of first-year dairy manure nitrogen availability or recovery using nitrogen-15 and other techniques.

Measurements of dairy manure nutrient availability to crops typically show great variability. Approaches that are more accurate are needed to improve manure management and reduce nutrient loss to the environment. In this study, we compared direct (15N recovery) and indirect (difference method [Diff Meth] and fertilizer equivalence [FE] approach) methods of determining first-year dairy manure N availability or recovery during three cropping seasons. A field experiment was conducted on a Plano silt loam (fine-silty, mixed, superactive, mesic Typic Argiudolls) planted to corn (Zea mays L.). Plots received either manure, fertilizer N, or no N. Microplots receiving 15N-labeled manure were also established each study year. Manure was applied to a new plot each cropping season. Whole-plant N uptake was the best crop parameter to use for FE estimates. Estimates of N availability by relative effectiveness (Rel Eff), which are derived from the Diff Meth, and FE were similar (32 and 41%, respectively) and higher than unlabeled N or 15N recovery measurements because these indices factor in N use efficiency. Measures of the Rel Eff of manure N use were highly affected by control plot N uptake. The FE approach is less influenced by control plots, but it requires the inclusion of several more treatments and use of mathematical functions to describe crop response to N. These limitations are reflected in the wide ranges obtained for N availability estimates (-60 to 148%). Although apparent N recovery by the Diff Meth (14%) or direct measurements of 15N recovery (16%) were close on average, variability tended to be much lower for the 15N method. In addition, the Diff Meth was highly dependent on initial soil conditions. Use of 15N-labeled manure, although more costly and time-consuming, provided more consistent and reliable results.

Biological Availability↗

PubMed2006

Global gene expression during nitrogen starvation in the rice blast fungus, Magnaporthe grisea.

Efficient regulation of nitrogen metabolism likely plays a role in the ability of fungi to exploit ecological niches. To learn about regulation of nitrogen metabolism in the rice blast pathogen Magnaporthe grisea, we undertook a genome-wide analysis of gene expression under nitrogen-limiting conditions. Five hundred and twenty genes showed increased transcript levels at 12 and 48 h after shifting the fungus to media lacking nitrate as a nitrogen source. Thirty-nine of these genes have putative functions in amino acid metabolism and uptake, and include the global nitrogen regulator in M. grisea, NUT1. Evaluation of seven nitrogen starvation-induced genes revealed that all were expressed during rice infection. Targeted gene replacement on one such gene, the vacuolar serine protease, SPM1, resulted in decreased sporulation and appressorial development as well as a greatly attenuated ability to cause disease. Data are discussed in the context of nitrogen metabolism under starvation conditions, as well as conditions potentially encountered during invasive growth in planta.

Amino Acids↗