ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Ihre E-Mail wurde erfolgreich gesendet. Bitte prüfen Sie Ihren Maileingang.

Leider ist ein Fehler beim E-Mail-Versand aufgetreten. Bitte versuchen Sie es erneut.

Vorgang fortführen?

Exportieren
Filter
  • Life and Medical Sciences  (6)
  • Fynbos  (4)
  • Biochemistry and Biotechnology  (2)
  • Wiley-Blackwell  (8)
  • Springer  (4)
  • American Association for the Advancement of Science
  • American Meteorological Society (AMS)
  • American Physical Society
Sammlung
Verlag/Herausgeber
  • Wiley-Blackwell  (8)
  • Springer  (4)
  • American Association for the Advancement of Science
  • American Meteorological Society (AMS)
  • American Physical Society
Erscheinungszeitraum
  • 1
    ISSN: 1432-1939
    Schlagwort(e): Nitrogen isotope discrimination ; Cape floristic region ; Fynbos ; Strandveld ; Acacia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract This study examines the impacts of woody, N2-fixing invasive Acacia spp. on the patterns of nutrient cycling in two invaded ecosystems of differing nutrient status in the Cape floristic region. Patterns of soil nutrient mineralization were measured by a field incubation method while the significance of the fixation process in altering nutrient cycling was assessed by the δ15N natural abundance technique. The results confirm earlier reports that invasion by woody shrubs results in organic matter and nutrient enrichment of surface soils of both ecosystems. However, patterns of nutrient availability (phosphorus and nitrogen) were not necessarily enhanced. In the more fertile strandveld both phosphorus and nitrogen (significant at P〈0.10) showed trends towards enhanced annual mineralization rates upon invasion, while in the low nutrient fynbos system only phosphorus followed this trend. It is unclear whether this differential response is a consequence of plant- or soil-derived feedbacks on the decomposition processes in each system. The δ15N values of the soils from the invaded sites of both ecosystems indicated a strong influence of the alien species on the soil nitrogen component. However, as with other studies of natural ecosystems, the contribution of nitrogen from fixation could not be readily quantified with the δ15N natural abundance method because of problems in selecting suitable non-N2-fixing reference plants. A technique of disrupting nodule structure and function, by fumigation with O2, to obtain the δ15N value of a non-N2-fixing speciment of the study species was tried and found to overcome some of the problems associated with the lack of suitable reference plants. With this technique it was possible to detect the almost total dependence of A. saligna on N2-fixation in the fynbos soils with their low nitrogen mineralization rates. In the strandveld ecosystem with much higher soil nitrogen release rates A. cyclops was only partly dependent on fixation (about half) for its nitrogen. The nutrient enrichment of both ecosystems and trends towards enhanced rates of nutrient mineralization could have profound implications on the long-term success of alien invader clearing operations and the restoration of the indigenous flora at these sites.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 2
    ISSN: 1432-1939
    Schlagwort(e): Allocation patterns ; Restionaceae ; Nitrogen ; Dry mass ; Fynbos
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The annual growth pattern of male plants of the endemic, dioecious fynbos species, Thamnochortus punctatus, revealed sequential growth of the various below-and above-ground organs. Root and rhizome development were favoured in the wet winter months while culm elongation occurred in the warmer but drier spring to summer period. The reproductive phase of development followed in the hot dry summer and autumn. The asynchronous pattern of growth is suggested to enable the plant to maximize utilization of scarce resources within the confines of the environmental controls determined by the mediterranean-climate. Maximum root and rhizome activity in the rainy season enabled the plant to absorb and store nitrogen in mature culms for later above ground organ development. As the absorption of nitrogen from senscing material is essential for this pattern of organ development to assist in alleviating nutrient scarcity the high degree of nitrogen reabsorption, 35 to 70% for branches and culms respectively, shows the potential importance of asynchronous organ growth in overcoming nitrogen limitation of plant growth. Comparisons of dry mass and nitrogen allocation patterns indicate that developmental strategies employed by evergreen, perennial plants in climatically and edaphically constrained environments cannot be deduced from biomass allocation patterns alone as they do not appear to reflect strategies evolved to overcome nutrient limitation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Oecologia 81 (1989), S. 412-417 
    ISSN: 1432-1939
    Schlagwort(e): Myrmecochory ; Fynbos ; Regeneration ; Fire ; Nutrient
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Leucospermum conocarpodendron (L.) Buek (Proteaceae) seedlings were excavated several months after a fire in Cape fynbos. Seedlings under burnt parental skeletons had short hypocotyls (mean 25 mm) indicating passive dispersal whereas seedlings in the open were more deeply buried (mean 48 mm) by ants. Soil nutrient concentrations at the site of germination were negatively related to depth of burial and distance from parent. Ant dispersal resulted in seedlings emerging in soils with lower nutrient concentrations than passively dispersed seeds. Tissue analysis supported the soil results with lower P content in seedlings from open (ant dispersed) sites. Seedling survival in the first year of establishment was also lower in open sites, but not significantly so. However seedlings were slightly taller in the open. The results of this study, the first on naturally occurring intraspecific variation in myrmecochory, strongly contradict current explanations for the high incidence of myrmecochory in nutrient poor environments.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Plant ecology 130 (1997), S. 143-153 
    ISSN: 1573-5052
    Schlagwort(e): Community boundaries ; Fynbos ; Nitrogen ; Phosphorus ; Soils
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The relationship between changes in soil nutrient characteristics and fynbos community boundaries was investigated near Cape Agulhas, South Africa. Soil characteristics relating to total nutrient content (pH, total N and total P, organic carbon, and various cations) were assessed at sites along three transects crossing the boundaries between five plant communities. Dynamics of available N and P in soils of three communities were studied in the field over one year, using ion-exchange resins. There was a wide range in the degree of change in soil nutrient content across different community boundaries. The characteristics that varied most were pH, total N, Ca and total P. Differences in available nutrients among soils indicated that the communities in this landscape were associated with a mosaic of N and P availability. It is proposed that spatial variation in soil nutrient availability rather than total soil nutrient contents may be important in explaining landscape-level species distributions and community composition in nutrient-poor mediterranean-climate ecosystems.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 5
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 49 (1996), S. 456-466 
    ISSN: 0006-3592
    Schlagwort(e): microcarrier culture ; turbulent mixing ; 3-D particle tracking ; energy dissipation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Three-dimensional particle tracking velocimetry (3-D PTV), a modern, quantitative, visualization tool, has been applied to the characterization of the flow field in the impeller region of cell culture reactor vessels. The experimental system used here is a 250-mL microcarrier spinner vessel. The studies were conducted at three different agitation rates, 90, 150, and 210 rpm, corresponding to healthy, mildly damaging, and severely damaging shear intensities, respectively. The flow can be classified into three regions: a predominantly tangential (azimuthal) flow generated by the impeller; a trailing vortex region coming off the impeller tip; and a converging flow region close to the center of the vessel. The latter two are the regions of highest velocity gradients. Energy dissipation rates due to mean velocity gradients were also calculated to characterize the impeller stream. Local specific energy dissipation rates 〉 10,000 erg/(cm3sec) · have been measured. It is proposed that the critical regions for microcarrier culture damage due to impeller hydrodynamics are the trailing vortex region and the high energy converging flow region. Graphical representation of the mean velocity flow fields and the distribution of energy dissipation rates in the impeller region are also presented here. The merits of using the dissipation function (measure of specific energy dissipation rate) as a possible scale-up parameter are also discussed. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 6
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 51 (1993), S. 41-46 
    ISSN: 0730-2312
    Schlagwort(e): CheY ; CheZ ; response regulators ; histidine kinase ; switch complex ; Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: The signal transduction system that mediates bacterial chemotaxis allows cells to moduate their swimming behavior in response to fluctuations in chemical stimuli. Receptors at the cell surface receive information from the surroundings. Signals are then passed from the receptors to cytoplasmic chemotaxis components: CheA, CheW, CheZ, CheR, and CheB. These proteins function to regulate the level of phosphorylation of a response regulator designated CheY that interacts with the flagellar motor switch complex to control swimming behavior. The structure of CheY has been determined. Magnesium ion is essential for activity. The active site contains highly conserved Asp residues that are required for divalent metal ion binding and CheY phosphorylation. Another residue-at the active site, Lys109, is important in the phosphorylation-induced conformational change that facilitates communication with the switch complex and another chemotaxis component, CheZ. CheZ facilitates the dephosphorylation of phospho-CheY. Defects in CheY and CheZ can be suppressed by mutations in the flagellar switch complex. CheZ is thought to modulate the switch bias by varying the level of phospho-CheY. © 1993 Wiley-Liss, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 7
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Biologie in unserer Zeit 29 (1999), S. 364-370 
    ISSN: 0045-205X
    Schlagwort(e): Life and Medical Sciences
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Bioindikatoren sind lebende Anzeiger für Umweltfaktoren. Flechten, die vordergründig unscheinbaren Doppelwesen aus Pilz und Alge, können auskunft über das Ausmaß der Luftbelastung einer Region geben. SIe werden in der Umweltüberwachung neben anderen Bioindikatoren unter Verwendung teilweise hoch standardisierter Verfahren eingesetzt. Mit entsprechender Anleitung können jedoch auch Schülerinnen und Schüler der Jahrgangsstufen 10 bis 13 oder erwachsene Laien Flechtenkartierungen durchführen und so Information über den Zustand der Luftqualität ihrer Region erhalten. Die gewonnenen Daten bieten eine gute Grundlage für weiterführend Auswertungen und Arbeiten im Bereich Stadt- oder Landschaftsökologie (Abbildung 1).
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 8
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    BioEssays 6 (1987), S. 199-203 
    ISSN: 0265-9247
    Schlagwort(e): Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Medizin
    Notizen: Bacteria adapt to changes in their environment by altering their metabolism, turning on and off genes, and moving toward favorable conditions. Recent results indicate that a common molecular logic may underlie the decision-making processes by which these simple cells adjust to their surroundings.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 9
    ISSN: 0173-0835
    Schlagwort(e): Polyacrylamide gel electrophoresis ; Single-strand conformation polymorphism ; Automated sequencer ; p53 gene ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: We report a new nonradioactive method to detect sequence changes, including single-base substitutions through shifts in electrophoretic mobility using an automated fluorescence sequencer (ALFexpress, Pharmacia, Biotech) connected to external cooling equipment. Single strands were identified by incorporation of fluorescein-labeled primers during amplification and subsequent laser detection at the bottom of the gel. The amplified polymerase chain reaction (PCR) products were heat-denatured and loaded onto a polyacrylamide gel under nondenaturing conditions and strict control of constant low temperature. Peak shifts in the fluorogram indicated mutations. A novel gel composition improved the detection rate for mutations considerably. Automatic analysis of single-strand conformation polymorphism (SSCP) gels saves time and costs, and is highly reproducible. The method was applied for mutation screening in exon 7 of the p53 tumor suppressor gene in DNA of freshly frozen soft tissue tumors. The mutation spectrum and frequency in exon 7 of the p53 gene are discussed with respect to oncogenesis in soft tissue sarcomas.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 10
    ISSN: 0021-9541
    Schlagwort(e): Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Medizin
    Notizen: The opossum kidney (OK) cell was used as a model to test the hypothesis that estrogen directly affects proximal renal tubular epithelial cells. To demonstrate the expression of estrogen receptor in OK cells, we developed an approach using reverse transcription and the polymerase chain reaction. Analysis of the DNA amplified with nested primers revealed the predicted size fragment and restriction enzyme digestion products. To demonstrate the functional effects of estrogen, OK cells at confluence were preincubated in serum-free medium for 7-10 days with or without 17β-estradiol. Bovine PTH(1-34) (bPTH(1-34)) then stimulated a dosedependent intracellular accumulation of cAMP that was maximal after 1 min and then gradually declined. Cyclic AMP in the medium slowly increased over 60 min. Preincubation with 17β-estradiol did not affect cell proliferation as measured by total protein content but caused an inhibition of bPTH(1-34)-stimulated intracellular cAMP accumulation that was maximal at 10-11M 17β-estradiol (71 ± 3% control, p 〈 .001). bPTH(1-34) also increased cAMP release into the medium, an effect maximal using 10-10M 17β-estradiol (118 ± 3% control, p 〈 .001). Preincubation with the inactive isomer 17α-estradiol caused no changes in cAMP accumulation or release. Coincubation with the antiestrogen tamoxifen blocked the effects of 17β-estradiol. Sodium-dependent phosphate transport was: (1) inhibited by 2-h incubations with 10-8 or 10-10 M bPTH(1-34) and not affected by preincubation with 17β-estradiol, and (2) not inhibited by a 20-min incubation with 10-8 M bPTH(1-34) unless cells were preincubated with 10-8 M 17β-estradiol, suggesting that any possible effects of estrogen on phosphate transport are not directly mediated by changes in cAMP. These studies demonstrate the presence of estrogen receptor mRNA in OK cells as well as direct and specific effects of physiologic concentrations of estrogen on cAMP accumulation in these cells. This system may be a good model for further study of estrogen and PTH effects on the kidney.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
Schließen ⊗
Diese Webseite nutzt Cookies und das Analyse-Tool Matomo. Weitere Informationen finden Sie hier...