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Digitale Medien

Performance of two Picea abies (L.) Karst. stands at different stages of decline (1988)

Oren, R. ; Werk, K. S. ; Schulze, E.-D. ; [weitere]

Springer

Oecologia 77 (1988), S. 151-162

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ISSN: 1432-1939

Schlagwort(e): Forest decline, Spruce (Picea abies) ; Nitrogen ; Magnesium

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary A declining Picea abies (L.) Karst. stand produced as much foliage and branches as a healthy stand but less stemwood at a similar leaf area index and climate. Nutrient analyses revealed that most biomass components at the declining site had lower concentrations of calcium and magnesium, but similar nitrogen and potassium (except for lower potassium in younger needles) and higher phosphorus, manganese and aluminum than the respective components at the healthy site. Comparison of these data with the results from studies on the nutrition and growth of P. abies seedlings (Ingestad 1959) led to the conclusion that the healthy stand is in a balanced nutritional state, while trees at the declining stand have only 56% of the foliar magnesium concentration required to permit growth at a rate which could be achieved at their nitrogen status. It appears that acidic deposition, which involves an input of nitrogen and a leaching of cations from the soil, causes an imbalance in the availability of nitrogen and magnesium. Growth is eventually reduced as magnesium becomes limiting.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00379181

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Digitale Medien

Distribution of plasma membrane rosettes and kinetics of cellulose formation in xylem development of higher plants (1986)

Schneider, B. ; Herth, W.

Springer

Protoplasma 131 (1986), S. 142-152

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ISSN: 1615-6102

Schlagwort(e): Cellulose fibril formation ; Freeze-fracture ; Plasma membrane ; Rosette distribution ; Xylem development

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary Germ roots of several higher plants—maize (Zea mays), mung bean (Vigna radiata) and cress (Lepidium sativum)—were freeze-fractured without cryoprotection in order to confirm and extend the informations on frequency and distribution of plasma membrane particle complexes with respect to cellulose formation. In all three objects the PF of developing xylem elements showed rosette accumulations in the regions of wall thickenings. The rosette-distribution pattern ranges from random in a young stage, to more grouped in a probable intermediate stage to strictly localized in later stages. The frequency of rosettes increases from stage to stage. In all three objects the EF of developing xylem elements is relatively poor in particles. Observations of “terminal globules” were rare and undistinct. This leads to the assumption that rosettes on the PF and terminal globules on the EF are not part of the same complex. A comparison of the number and distribution of microtubules underlying the xylem wall thickenings with rosette frequency and distribution leads to the conclusion that there seem to be no direct connections between these two structures. Microtubules may be involved in grouping of rosettes, thus indirectly orienting microfibril deposition. Calculations based on the observed rosette frequencies and the amount of wall material formed indicate that in xylem development 1,000 nm elementary fibril per rosette per minute may be formed and that the active phase of one rosette may be about 10 minutes.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01285036

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Digitale Medien

Multiple-pulse 1H-NMR study of polystyrene gels (1985)

Geschke, D. ; Pöschel, K. ; Doskočilová, D. ; [weitere]

Weinheim : Wiley-Blackwell

Acta Polymerica 36 (1985), S. 645-648

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ISSN: 0323-7648

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Beschreibung / Inhaltsverzeichnis: Untersucht wurden 1H-FID- und MW4-Spektren vom mit Ethylendimethacrylat und Divinylbenzen vernetztem und mit CCl4, CDCl3 und Benzen gequollenem Polystyren. Die mit Hilfe von Vielimpulscyclen erreichbaren Linienverschmälerungen werden diskutiert und mit denen der MAR-Technik verglichen. Die Temperaturabhängigkeit der effektiven Relaxationszeit T2eff spiegelt die Dynamik lokaler Segmentprozesse wider.

Notizen: 1H-FID and MW4-pulse spectra of polystyrene crosslinked with ethylene dimethacrylate or divinylbenzene and swollen in CCl4, CDCl3 or benzene, are measured. Line-narrowing effects of multiple-pulse sequences are discussed and compared with those of the MAR-technique. The temperature dependence of the effective relaxation time T2eff reflects the dynamics of local segmental processes.

Zusätzliches Material: 5 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/actp.1985.010361201

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