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  • Electronic Resource  (14)
  • Inorganic Chemistry  (8)
  • Larrea tridentata  (4)
  • Glutamine synthetase  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 20 (1995), S. 137-146 
    ISSN: 1432-0789
    Keywords: Larrea tridentata ; Simulated rainfall ; Precipitation exclusion ; Soil drying effects ; Analysis of covariance ; Chihuahan Desert ; Mineralization rate ; Field capacity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Irrigation and rain-out shelters were used to simulate precipitation patterns of wet and dry years in the northern Chihuahuan Desert. Irrigation provided approximately double the long-term average monthly precipitation. Rain was excluded during the wet season, July-October, to simulate a dry year. N net mineralization in laboratory incubations was undectable at calculated water potentials less than -1 MPa. Witb increasing moisture, mineralization gradually rose to the highest observed rates near field capacity. There was no mineralization maximum at moisture contents below field capacity. Irrigation significantly increased the water potential and rainfall exclusion reduced water potentials to less than-8 MPa. The general absence of important irrigation effects may have resulted from the high natural precipitation during the experiment or because irrigation inputs were insufficient to increase microbial activity during very dry periods. Precipitation exclusion reduced ion capture during the warm-wet season. After allowing precipitation inputs to resume, NH 4 + -N capture was increased in the cool-dry seasons of both 1987–1988 and 1988–1989. NH 4 + -N capture more than doubled that predicted from the overall covariance of moisture input and ion capture, suggesting increased availability of N. An unusually hot, dry period in May and June 1989 was followed by a threeto fourfold increase in the warm-wet season NO 3 − +NO2−N capture compared to 1988. These data suggest that short droughts of about 3 months in length (both simulated and natural) increased N availability relative to moisture availability.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 82 (1990), S. 18-25 
    ISSN: 1432-1939
    Keywords: Desert shrubs ; Larrea tridentata ; Nitrogen cycling ; Insects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We tested the hypothesis that herbivorous insects on desert shrubs contribute to short-term nitrogen cycling, and increase rates of nitrogen flux from nutrient rich plants. Creosotebush (Larrea tridentata) shrubs were treated with different combinations of fertilizer and water augmentations, resulting in different levels of foliage production and foliar nitrogen contents. Foliage arthropod populations, and nitrogen in canopy dry throughfall, wet throughfall and stemflow were measured to assess nitrogen flux rates relative to arthropod abundances on manipulated and unmanipulated shrubs over a one-month period during peak productivity. Numbers and biomass of foliage arthropods were significantly higher on fertilized shrubs. Sap-sucking phytophagous insects accounted for the greatest numbers of foliage arthropods, but leaf-chewing phytophagous insects represented the greatest biomass of foliage arthropods. Measured amounts of bulk frass (from leaf-chewing insects) were not significantly different among the various treatments. Amounts of nitrogen from dry and wet throughfall and stemflow were significantly greater under fertilized shrubs due to fine frass input from sap-sucking insects. Increased numbers and biomass of phytophagous insects on fertilized shrubs increased canopy to soil nitrogen flux due to increased levels of herbivory and excrement. Nitrogen excreted by foliage arthropods accounted for about 20% of the total one month canopy to soil nitrogen flux, while leaf litter accounted for about 80%.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1939
    Keywords: Larrea tridentata ; Leaf demography ; Nutrient resorption ; Nutrient-use efficiency ; Photosynthesis ; Water-use efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the Chihuahuan Desert of southern New Mexico, both water and nitrogen limit the primary productivity of Larrea tridentata, a xerophytic evergreen shrub. Net photosynthesis was positively correlated to leaf N, but only in plants that received supplemental water. Nutrient-use efficiency, defined as photosynthetic carbon gain per unit N invested in leaf tissue, declined with increasing leaf N. However, water-use efficiency, defined as the ratio of photosynthesis to transpiration, increased with increasing leaf N, and thus these two measures of resource-use efficiency were inversely correlated. Resorption efficiency was not significantly altered over the nutrient gradient, nor was it affected by irrigation treatments. Leaf longevity decreased significantly with fertilization although the absolute magnitude of this decrease was fairly small, in part due to a large background of insect-induced mortality. Age-specific gas exchange measurements support the hypothesis that leaf aging represents a redistribution of resources, rather than actual deterioration or declining resource-use efficiency.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 81 (1989), S. 166-175 
    ISSN: 1432-1939
    Keywords: Desert shrubs ; Larrea tridentata ; Nitrogen ; Plant-insect interactions ; Phytophagous insects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We conducted a field study to test the hypothesis that creosotebush (Larrea tridentata) shrubs growing in naturally nutrient-rich sites had better quality foliage and supported greater populations of foliage arthropods than shrubs growing in nutrient-poor sites. Nutrient-rich sites had significantly higher concentrations of soil nitrogen than nutrient-poor sites. Multivariate analysis of variance revealed significant differences between high nutrient and low nutrient shrubs based on a number of structural and chemical characteristics measured. High nutrient shrubs were larger, had denser foliage, greater foliage production, higher concentrations of foliar nitrogen and water, and lower concentrations of foliar resin than low nutrient shurbs. Numbers of foliage arthropods, particularly herbivores and predators, were significantly higher on high nutrient shrubs. Shrub characteristics and foliage arthropod abundances varied considerably from shrub to shrub. Shrub characteristics representing shrub size, foliage density, foliage growth, and foliar nitrogen and water concentrations were positively correlated with arthropod abundances. Foliar resin concentrations were negatively correlated with foliage arthropod abundances. The positive relationship between creosotebush productivity and foliage arthropods is contradictory to the tenet that physiologically stressed plants provide better quality foliage to insect herbivores.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-072X
    Keywords: Nitrogen fixation ; Nitrogenase regulation ; Glutamine synthetase ; Methionine suofoximine ; Rhodospirillaceae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methionine sulfoximine (MSX), an irreversible inhibitor of glutamine synthetase of Rhodopseudomonas palustris restored nitrogenase activity to cells in which nitrogenase had been completely inhibited by ammonia switch-off. After addition of MSX, there was a lag period before nitrogenase activity was fully restored. During this lag, glutamine synthetase activity progressively decreased, and near the time of its complete inhibition, nitrogenase activity resumed. Nitrogenase switch-off by ammonia thus required active glutamine synthetase. Glutamine itself caused nitrogenase inhibition whose reversal by MSX depended on the relative ratio of MSX to glutamine. Unlike ammonia, glutamine inhibited nitrogenase under conditions where glutamine synthetase activity was absent. This indicates that glutamine is the effector molecule in nitrogenase switch-off, for instance by interacting with the enzymatic system for Fe protein inactivation. The effects of glutamine and MSX were also dependent on the culture age. Possible explanation for this and for the competitive effects are a common binding site within the regulatory apparatus for nitrogenase, or, in part, within a common transport system. Some observations with MSX were extended to Rhodopseudomonas capsulata and agreed with those in R. palustris.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-072X
    Keywords: Nitrogenase regulation ; Glutamine synthetase ; Ammonia switch-off ; Rhodopseudomonas palustris
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogenase activity in Rhodopseudomonas palustris is subject to a rapid switch-off in response to exogenous ammonia. When cells were grown on limiting nitrogen and eventually became nitrogen deficient, nitrogenase synthesis was fully derepressed but the enzyme was insensitive to ammonia. The transformation of ammonia-sensitive to ammonia-insensitive cells was a slow, but fully reversible process. The switch-off effect in ammonia-sensitive cells paralleled changes in the adenylylation state of glutamine synthetase. Ammonia-insensitive cells, however, showed similar changes in glutamine synthetase activity although nitrogenase activity was unaffected. We conclude that nitrogenase regulation and adenylylation of glutamine synthetase are independent processes, at least under conditions of nitrogen deficiency.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 109 (1976), S. 306-313 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Formation and Structure of the Pentabromocarbonate Anion [CBr5⊖]n - On the Oxidation of En-aminesOxidation of enamines 5 with tetrabromomethane yields stable crystalline pentabromocarbonates 6, which may easily be converted into the corresponding perchlorates 7. From the pentabromocarbonates, tetrabromomethane cannot be extracted either by organic solvents or by heating in vacuo; with silver nitrate, however, silver bromide can be precipitated from tetraphenylphosphonium pentabromocarbonate (9). If labelled 9 - prepared from tetraphenylphosphonium [82Br]bromide and tetrabromomethane - is treated with silver nitrate, all the activity is found in the silver bromide precipitate. This is clear evidence against a trigonal bipyramidal structure of the pentabromocarbonate anion CBr5⊖]n.
    Notes: Bei der Oxidation von Enaminen 5 mit Tetrabrommethan entstehen stabile kristalline Pentabromocarbonate 6, die sich leicht in die entsprechenden Perchlorate 7 überführen lassen. Aus den Pentabromocarbonaten kann Tetrabrommethan weder durch Extraktion mit organischen Solventien noch durch Erhitzen i. Vak. abgespalten werden, mit Silbernitrat kann jedoch aus Tetraphenylphosphonium-pentabromocarbonat (9)Silberbromid ausgefällt werden. Bei der Umsetzung von markiertem 9 - dargestellt aus [82Br] Tetraphenylphosphoniumbromid und Tetrabrommethan - mit Silbernitrat findet man die Gesamtaktivität im Silberbromid-Niederschlag. Dies spricht gegen die Struktur einer trigonalen Bipyramide für das CBr5⊖]n-Anion.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Combined with the sudden increase of the susceptibility of antiferromagnetic VO2 at a temperature of about 70°C, the electric conductivity of VO2 is strongly increased, too. Isomorphic substitution of V4+-ions by Ti4+-ions disturbs the antiferromagnetic interaction within the lattice. VO2—TiO2-mixed crystals exhibit higher susceptibilities and conductivities than pure VO2 does; there is a reduced increase of both the susceptibility and conductivity at about 70°C.The spectrum of reflection of VO2 is changed by Ti4+-ions in the same manner like that of pure VO2 when heated above 70°C.
    Notes: Mit dem sprunghaften Anstieg der Susceptibilität von reinem VO2 bei ∼ +70°C ist ein starker Anstieg der elektrischen Leitfähigkeit verbunden. Durch isomorphen Ersatz von V4+ durch Ti1+ werden die antiferromagnetischen Wechselwirkungen im VO2-Gitter gestört. Dies gibt sich an VO2—TiO2-Mischkristallen durch einen Anstieg der Susceptibilität und der Leitfähigkeit sowie durch eine Erniedrigung des Susceptibilitäts- und Leitfähigkeitssprunges in der Gegend von +70°C zu erkennen.Die Farbkurven von VO2 zeigen bei Einbau von Ti4+-Ionen in das VO2-Gitter die gleichen charakteristischen Veränderungen, wie sie bei reinem VO2 oberhalb +70°C auftreten.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 285 (1956), S. 287-296 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Es wird die Darstellung von zwei Natriumvanadaten(IV), Na2VO3 und Na2V2O5, beschrieben. Entsprechende Lithiumvanadate(IV) konnten nicht erhalten werden; die Umsetzung zwischen Li2O und VO2 führt bei 700° zu Vanadin(III)- und Vanadin(V)-verbindungen.CaVO3, aus CaO und VO2 bei 800° erhältlich, kristallisiert im Perowskitgitter mit a = 3,75 ± 0,01 kX.Zwischen Kobaltvanadin(III)-spinell, CoV2O4 mit a = 8,39 kX und Kobaltvanadin(IV)-spinell, Co2VO4, existiert eine Mischphase, die von 0-90 Mol-% VO2 reicht. Der reine Vanadin(IV)-spinell läßt sich nicht darstellen, weil bei der Umsetzung von VO2 mit CoO in geringem Umfang stets eine Disproportionierung des V4+ eintritt. Eine dem Kobalttitan(IV)-oxyd, CoTiO3, entsprechende Verbindung tritt im System CoO—VO2 nicht auf, doch lassen sich im Titanat unter Erhaltung der Ilmenitstruktur bis 50% der Ti4+-Ionen durch V4+-Ionen ersetzen.Auch die Umsetzung von 1 VO2 mit 2 MgO führt, wie jetzt gezeigt werden kann, zu keinem einheitlichen Produkt, so daß es den Anschein hat, daß reine Vanadin(IV)-spinelle, Me2VO4 (Me = Co, Zn, Mg, Mn) wegen des leichten Eintritts von Disproportionierungsreaktionen nicht existenzfähig sind.Im System Nickel - Vanadin - Sauerstoff tritt keine Spinellphase auf.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 25 (1892), S. 1261-1270 
    ISSN: 0365-9496
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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