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  • 11
    Digitale Medien
    Digitale Medien
    Effect of supercooling and freezing on photosynthesis in freezing tolerant leaves of Afroalpine ‘giant rosette’ plants (1987)
    Springer
    Oecologia 72 (1987), S. 366-371 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Chlorophyll fluorescence ; Supercooling ; Frozen leaves ; Photosynthesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The effect of supercooling and freezing on the photosynthetic capability of representatives of the permanent frost hardy giant rosette plants Dendrosenecio keniodendron, D. brassica and Lobelia telekii, of the tropical alpine regions was investigated with the non-invasive chlorophyll a fluorescence technique. While supercooling, normal chlorophyll a fluorescence kinetics exhibiting the sequence 0, I, (D), P, S, M, were recorded, however with some retardation of both, the fast and the slow characteristics as compared to those obtained at day-time temperature. As long as the leaves remained unfrozen, the rise of the variable fluorescence F ν from the level 0 to P was inversely related to a drop of the temperature from about 0°C to-8°C. The increase of F ν with lower temperature is understood to result from a decrease of the velocity of the quenching reactions while photoreduction of the primary electron acceptor appeared to be unimpeded. The second fluorescence maximum (M), usually interpreted to indicate the commencement of the biochemical reactions of photosynthesis was consistenly to be observed during supercooling. Fluoescence induction kinetics of frozen leaves showed only fast rise to presumably F max which was not followed by a significant decay for as long as 4 min. The lack of substantial quenching indicates that in the freeze-dehydrated state neither reoxidation of the primary acceptor nor energetization of the thylakoid membrane was accomplished. This effect however was immediately and fully reserved upon thawing of the leaves when the usual fluorescence induction kinetics as well as normal rates of CO2-uptake were observed. Thus the permanent frost-hardy afroalpine plants do not exhibit any even short-term memory effect of the nocturnal frost on such a delicate process as is photosynthesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00377565
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  • 12
    Digitale Medien
    Digitale Medien
    Factors influencing hydrocarbon degradation in three freshwater lakes (1985)
    Springer
    Microbial ecology 11 (1985), S. 127-137 
    Details
    ISSN: 1432-184X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The mixed microbial flora of 3 lakes in Ohio with differing histories of hydrocarbon pollution was examined in relation to the ability to use hydrocarbons. Weathered kerosene was spiked with naphthalene, pristane, 1,13-tetradecadiene, andn-hexadecane and added to water-sediment mixtures from the 3 lakes, and utilization of the 4 marker hydrocarbons was measured. Each of the marker hydrocarbons was metabolized; naphthalene was the most readily used and pristane was the most resistant. Values for dissolved oxygen suggest that oxygen did not limit hydrocarbon degradation in the water column at any site examined. Nutrient addition studies indicated that nitrogen and phosphorus limited hydrocarbon degradation at all sites examined. Maximum numbers of heterotrophic bacteria were detected when the water temperature was 10°C or higher. The data indicate that temperature limits hydrocarbon degradation in the winter, except at a site which had been impacted by an oil spill and which received chronic inputs of hydrocarbons and nutrients. In samples from that site, all 4 marker hydrocarbons were degraded at 0°C. Results of temperature and nutrient-addition experiments suggest that different seasonal populations of hydrocarbon users are selected at that site, but not at other lake sites.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02010485
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  • 13
    Digitale Medien
    Digitale Medien
    Reassessment of root competition for P of field-grown maize in pure and mixed cropping (1988)
    Springer
    Plant and soil 106 (1988), S. 299-301 
    Details
    ISSN: 1573-5036
    Schlagwort(e): lupin ; maize ; phosphate ; root competition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Root competition for phosphate (P) in the field was calculated with maize i) as singly grown plants, ii) in pure cropping and iii) in mixed cropping with lupin. The experimentally determined parameters used for this purpose were thein situ root-distance pattern as registered by autoradiography and the P-depletion cylinder around a maize root as determined autoradiographically under radial diffusional flow. The results do not indicate any competition for P between roots of adjacently grown plants in either pure or mixed cropping. On the other hand, the P-depletion cylinders of approximately one third of the roots of an individual maize plant were found to overlap. However, when allowance was made for the concentration gradients within a depletion cylinder, the actual competition for phosphate was less than 1%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02371230
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  • 14
    Digitale Medien
    Digitale Medien
    Development and replenishment of the P-depletion zone around the primary root of maize during the vegetation period (1987)
    Springer
    Plant and soil 101 (1987), S. 247-255 
    Details
    ISSN: 1573-5036
    Schlagwort(e): freeze-cutting ; dynamics ; depletion zone ; root longevity ; maize ; P-deficiency ; phosphate ; radioautography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The dynamics of the development and replenishment of P-depletion zones around the primary root of maize (Zea mays L. cv ‘Garbo’) was studied during a vegetation period (80 days) under greenhouse conditions in a loamy sand of low P-availability. A recently described freeze-cutting technique was used to determine radial diffusion of labelled phosphate to the primary root. The development of the depletion zone was biphasic. In the initial phase after two days of growth of the primary root in a soil layer labelled with33P a minimum of isotopically exchangeable P (EP) was observed which had decreased to about 30% of its original amount at the root surface. At that time the corresponding P-concentration in the soil solution was calculated to be as low as 5×10−7 M. The depletion zone had already spread 0.4 mm from the root surface. During the second phase, between the 10th and 20th day of plant growth the concentration of EP at the root surface increased slowly but did not change markedly. However, the depletion zone continued to spread and after the 20th day of growth reached its maximal diameter (1.07 mm from the root surface) but remained completely within the root hair cyclinder; the single root hairs never exceeded 1.14 mm in length. The biphasic growth of the depletion zone was probably caused by proton extrusion of the root tip. Acidification of the soil solution from pH 5.8 to about 3.9 results in an about 3-fold rise of the concentration of desorbed phosphate and might also have activated acidophilic P-translocators of the root during the initial phase. Anion over cation uptake normally prevailing during the later stage of root development might resulted in a rise of the soil pH within the root hair zone. Consequently P-availability, as well as P-uptake capacity declined, but P-uptake by the seminal root still continued until the 20th day. Subsequently, the P-concentration within the depletion zone increased again while simultaneously its extent was reduced until it was almost completely replenished after 60 days indicating a loss of P-uptake capacity of the primary root. Within the root tissue33P was accumulated to about twice the concentration of that in the undepleted soils. This accumulation corresponded to periods of high uptake due to the development of root laterals. In the root cortex a high P-content was observed during the first 30 days of growth. At the onset of the reproductive stage of the plant the P-content of the shoot and especially in the developing seeds rose considerably at the cost of phosphate stored in the root cortex. The accumulation of33P in the root tissue indicated that nutrient gain was mainly achieved during the early stages of plant development and that P was temporarily stored to some extent within the root system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02370652
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  • 15
    Digitale Medien
    Digitale Medien
    High-spin spectroscopy of168Hf (1987)
    Springer
    The European physical journal 327 (1987), S. 397-402 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 21.10.Re ; 23.20.Lv ; 27.70.+ q
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The nucleus168Hf was studied up to spin (38+) in the yrast band and to spins (41−) and (38−) in the lowest two negative-parity bands. The onset of a proton alignment (h9/2 or i13/2 quasiparticles) is observed in these three bands for the highest transitions. A new band with even spins and negative parity was found. The interaction strength between the ground-state band and theAB band is measured.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01289564
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  • 16
    Digitale Medien
    Digitale Medien
    High-spin spectroscopy of162Hf (1988)
    Springer
    The European physical journal 329 (1988), S. 289-299 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 21.10.Re ; 23.20.Lv ; 27.70.+q
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Excited states in162Hf were investigated up to spinI ≈ 38 using the anti-Comptonspectrometer array HERA with 21 detectors. In addition, some information was obtained on161Hf. The analysis of triple coincidences was crucial for the construction of the level schemes. The results are interpreted within the framework of the cranked shell model and are compared to neighbouring isotopes and isotones, showing Fermi level and deformation effects. The systematic behaviour of the band crossings in the Hf isotopes and theN=90 isotones is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01290234
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  • 17
    Digitale Medien
    Digitale Medien
    In situ-determination of the phosphate-gradient around a root by radioautography of frozen soil sections (1987)
    Springer
    Plant and soil 97 (1987), S. 407-418 
    Details
    ISSN: 1573-5036
    Schlagwort(e): Freeze-cutting technique ; In situ phosphate depletion profile ; Maize ; Radioautography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Summary A radioautographic method is described which allows the determination of phosphate concentration profiles around a root in situ,i.e. under conditions of radial diffusional flow. The device consisted of a soil column containing a distinct layer labelled with33P which was kept separated from the rest of the content of a (modified) Kich-Brauckmann vessel. The primary root of a maize plant was directed into the special soil core whereas the other roots were allowed to develop into the unlabelled portion of the pot. Two or five days after the roots had penetrated the labelled soil sections the soil blocks were immediately frozen in liquid nitrogen and, ommitting any further embedding procedures, sliced perpendicular to the growth direction of the root by means of a stone cutting saw. From the frozen soil slices radioautograms were prepared and densitometrically analysed for phosphate content within and outside the root. The P-depletion zones around the root as well as areas of P-accumulation within the root coincided well with anatomical and morphological root parameters as determined with maize plants grown under similar conditions thus mutually corroborating the findings. Interestingly, the P-depletion zone around the primary root did not exceed the area of the root hair cylinder. Although soil composition and the extent of water supply to the pot somewhat limit the applicability of the presented technique, it should be appropriate for the investigation of a variety of agricultural soils. Since laterals did not interfere with the analysis this method should also allow long-term studies to be performed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02383231
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