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  • 1975-1979  (30)
  • 1905-1909  (24)
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  • 11
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In a previous paper seasonal shifts of the temperature optimum (OP) and of the upper temperature compensation point (CP) of net photosynthesis were described for Hammada scoparia growing wild, and for Prunus armeniaca cultivated in the Negev Desert (Israel). In this paper the relationships between these shifts and the microclimatic conditions, plant-water relations, and plant development are studied. The energy budged of the thin, round photosynthesizing stems of H. scoparia growing in an open desert habitat differes from that of the broad leaves of P. armeniaca within the orchard. This explains the fact that daily maximum temperatures of the apricot increased until August and September, whereas maximum temperatures of H. scoparia reached a peak in May and June and decreased thereafter during the second half of the growing season. For H. scoparia a correspondence was found between the daily maximum tissue temperatures (and also the average temperatures of the warmest periods of the day) and the seasonal changes of the OP and CP values. This may indicate that the shifts in the temperature sensitivity of net photosynthesis of this plant are adaptations to the temperature conditions of the plant. This, however, cannot be the case for P. armeniaca, where during the second part of the growing season a period of rising leaf temperatures coincides with a period of decreasing OP and CP values. Therefore, the seasonal changes of the temperature dependence of net photosynthesis of P. armeniaca could not always be considered an adaptation to the prevailing temperature conditions of the plant. In this case, the changes in temperature sensitivity of photosynthesis could be due to developmental processes such as aging. In both lants the seasonal changes of the OP and CP values correspond to changes of the daily photoperiod and to changes of the daily average light intensity. It appears possible that this correlation indicates a causal relationship.
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Net photosynthesis of Picea abies was measured in a spruce forest in northern Germany with temperature- and humidity-controlled cuvettes in 4 different crown layers on shoots of different ages. These measurments were performed such that temperature and humidity either followed ambient conditions or were kept constant. Annual courses of light-, temperature-, and humidity-related net photosynthesis were determined. Spruce had a remarkably constant rate of CO2 uptake from April to September for 1-year and older needles. Light saturation was achieved at 25 klx. Current year needles had the highest rates of CO2 uptake in early summer, but these rates decreased by autumn. Photosynthetic capacity decreased with needle age and, on a dry weight basis, it was higher in the shade than in the sun crown. The temperature optimum was between 13 and 23° C. Photosynthesis in spruce decreased when air humidity was low. The effect of the natural weather conditions on photosynthetic capacity was determined. The habitat is characterized by a high frequency of low light intensities (75% of total daytime below 20 klx) and cool temperatures (80% of daytime between 9 and 21° C). Low air humidity was only present when light intensities were high. The major limiting factor for production was low light intensities, which reduced photosynthetic capacity in the sun crown to 42% below maximum possible rates. Adverse temperatures reduced CO2 uptake by 28% and large water vapor pressure deficits reduced rates by only 2% compared with maximum possible rates. The limited adaptation to light is discussed.
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  • 13
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Within the area of its natural distribution in South West Africa, Welwitschia mirabilis has a less negative δ13C value than C3 plants and a more negative δ13C value than C4 species. This indicates that Welwitschia m. assimilates CO2 partially via CAM when growing in its natural habitat. The difference between the δ13C values of Welwitschia m. and of the C3 species is significant in the savanna, whereas it is only small and statistically not significant in the grassland zone. The proportion of CO2 fixed via CAM is largest in the coastal desert zone. There was no correlation between the δ13C values and the Cl- or ash content of the tissue. Thus, CAM in Welwitschia m. seems not to be induced by salt stress. There is no change in the δ13C values along the persistent Welwitschia m. leaf. The present data indicate that on a broad geographical scale in the area of distribution temperature regime, and water stress as a modifying factor, determine CAM in Welwitschia m. The ecological implications are discussed by comparing the behaviour of Welwitschia m. with other CAM, C3 and C4 species of the accompanying flora.
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  • 14
    ISSN: 1432-2048
    Keywords: Humidity response ; Stomata ; Transpiration ; Water potential ; Water stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Short-term (hours) changes in plant water status were induced in hazel (Corylus avellana L.) by changing the evaporative demand on a major portion of the shoot while maintaining a branch in a constant environment. Stomatal conductance of leaves on the branch was influenced little by these short-term changes in water status even with changes in leaf water potential as great as 8 bars. Long-term (days) changes in plant water status were imposed by soil drying cycles. Stomatal conductance progessively decreased with increases in long-term water stress. Stomata still responded to humidity with long-term water stress but the range of the conductance response decreased. Threshold responses of stomata to leaf water potential were not observed with either short-term or long-term changes in plant water status even when leaves wilted. It is suggested that concurrent measurements of plant water status may not be sufficient for explaining stomatal and other plant responses to drought.
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 47 (1908), S. 67-68 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 47 (1908), S. 76-76 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 42 (1909), S. 4654-4659 
    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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  • 18
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 39 (1906), S. 2932-2933 
    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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  • 19
    Publication Date: 1908-01-01
    Print ISSN: 1618-2642
    Electronic ISSN: 1618-2650
    Topics: Chemistry and Pharmacology
    Published by Springer
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  • 20
    Publication Date: 1908-01-01
    Print ISSN: 1618-2642
    Electronic ISSN: 1618-2650
    Topics: Chemistry and Pharmacology
    Published by Springer
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