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  • 1
    Electronic Resource
    Electronic Resource
    Water use efficiency of two succulents with contrasting CO2 fixation pathways (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 20 (1997), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Two succulents with similar growth forms but different types of photosynthesis, Cotyledon orbiculata (crassulacean acid metabolism, CAM) and Othonna opima (C3 pathway), were investigated with respect to the modulation of water use efficiency (WUE) during the transition from the rainy season to subsequent drought. Environmental conditions were simulated in a controlled-environment experiment on the basis of data collected in the habitat of the two species in the southern Namib desert. Experiments included one or more periods of hot bergwind, which frequently occurs in this region. When water was readily available, daily net CO2 fixation was similar in the two species. This result confirms that the daily CO2 fixation of CAM plants is as high as that of morphologically similar C3 plants adapted to the same habitat. As expected, both species reduced CO2 fixation and water loss through transpiration during simulated hot bergwind periods and their WUE values increased. However, after the second hot bergwind period, nearly identical WUEs were recorded: 41.0 and 40.0 mmol mol−1 for C. orbiculata and O. opima, respectively. Therefore the statement that a CAM plant is a better ‘water saver’ than a C3 plant does not necessarily hold for CAM and C3 plants with similar growth forms growing under the same environmental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1997.d01-16.x
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  • 2
    Electronic Resource
    Electronic Resource
    Water economy and photosynthesis of the CAM plant Senecio medley-woodii during increasing drought (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 11 (1988), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract CO2 gas exchange, transpiration and water uptake of the succulent Senecio medley-woodii were monitored simultaneously during a 10 day period of increasing drought. The measurements were performed with a combination of a CO2 gas exchange chamber and a potometer system. Further, leaf water relations and CO2 gas exchange of a branched potted plant were measured during 15 days of water shortage. The enhancement of CO2 dark fixation at the beginning of drought modifies the leaf water relations according to the increased malate accumulation during the dark period. The enhancement of water uptake from dusk to dawn corresponds to the increase of Ψleaf during the same period. Therefore at the beginning of drought a short time improvement of plant water status through the increased CO2 dark fixation and malate accumulation can be maintained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1988.tb01800.x
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  • 3
    Electronic Resource
    Electronic Resource
    Spectral Properties of Juvenile and Adult Leaves of Piper betle and Their Ecological Significance (1977)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 41 (1977), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Juvenile and adult leaves of Piper betle L. were shown to have different spectral properties. A computer model was used to calculate the temperature of these leaves taking the energy balance approach. At high values of solar radiation, juvenile leaves with lower absorptivity in the visible and the near infrared show markedly lower temperatures than mature leaves. There is an ecological effect of high and low leaf temperatures on heat load and water stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1977.tb01515.x
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  • 4
    Electronic Resource
    Electronic Resource
    CO2 gas exchange and transpiration of Welwitschia mirabilis Hook. fil. in the central Namib desert (1982)
    Springer
    Oecologia 55 (1982), S. 21-29 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The diurnal course of CO2 gas exchange, 14CO2 incorporation, malate and citrate content, and traspiration of Welwitschia mirabilis were measured in one of its natural habitats, the Welwitschia-Vlakte in the central Namib desert (Namibia), in order to decide which CO2 fixation pathway is used by this gymnosperm. The CO2 gas exchange of Welwitschia is that of a C3 plant under arid conditions. Younger leaf parts show a two-peaked pattern of photosynthetic CO2 uptake whereas in older parts the morning peak is followed by net CO2 release during the rest of the day. The maximum rates of net photosynthesis decrease from 3.4 μmol m-2 s-1 in 1-year-old parts to 1 μmol m-2 s-1 in 7-year-old parts. No net CO2 uptake was detected during the night. The diurnal CO2 balance indicates that the old leaf parts live at the expense of the younger ones. Irrigation of Welwitschia plants resulted in an increased CO2 uptake throughout the light period with maximum rate of 4.1 μmol m-2 s-1. 14CO2 was only incorporated during the day. The water loss of Welwitschia by transpiration is considerable, reaching a peak value of 1.9 mmol m-2 s-1 around noon. Leaf conductance corresponds with the twopeaked pattern of CO2 uptake. Although there is no sign of a crassulacean acid metabolism in Welwitschia the leaf contains rather high amounts of malate (up to 200 μmol g-1 dry matter) and citrate (up to 250 μmol g-1 dry matter), which depend on leaf age but do not show any significant day-night oscillation. In spite of all this the δ13C values are in the range of-17.77 to-19.64‰. Possible reasons for such a high 13C content in a C3 plant are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386713
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  • 5
    Electronic Resource
    Electronic Resource
    Leaf temperatures and energy balance ofWelwitschia mirabilis in its natural habitat (1980)
    Springer
    Oecologia 44 (1980), S. 258-262 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Welwitschia mirabilis is a perennial desert plant with extremely large leaves (0.5–1.0 m broad, 1–2 m long). Leaf temperatures were measured in the field and the energy budget was calculated. The portions of the leaf which were kept above the ground had leaf temperatures which were only 4–6°C above air temperature. In the leaf portions which were in contact with the ground leaf temperatures were 6–12°C above air temperature (absolute maximum 51°C). The important feature in the energy budget ofWelwitschia mirabilis is its high reflectivity (38% of the global radiation). Only about 56% of the global radiation is absorbed by the thick leathery leaves. The energy loss due to convection is of the same order of magnitude as the reflection and it is abouy the same in the portions of leaf on and above the ground. The difference in leaf temperatures found in these portions is due to the loss of thermal radiation from the section of leaf above the ground to the cooler ground which is shaded by the leaf. The provision of a heat sink due to the large area of shade cast by these large leaves is of significance to the existence ofWelwitschia mirabilis in its arid habitats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00572688
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  • 6
    Electronic Resource
    Electronic Resource
    The significance of leaf pubescence for the absorption of global radiation by Tussilago farfara L. (1977)
    Springer
    Oecologia 29 (1977), S. 179-187 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The spectral properties of juvenile and adult leaves of Tussilago farfara L. were measured for the wave range from 400 to 1350 nm. The significance of leaf pubescence for the absorption of global radiation was determined. The absorption is lowered by epidermal harrs only for the visible part of the spectrum (400–1350 nm). Absorptivities of the infrared do not vary whether hairs are present or not. The spectral properties of the upper and the lower surfaces without hairs are not equal. The hairs on the lower surface increase the amount of infrared radiation that is reflected by the upper surface. As shown by calculations of the absorbed radiation, pubescence has little influence on energy input. If leaves are put in an inverse position, the absorption of the global radiation energy is lowered by 15% compared with the same leaf in the regular position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00345796
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  • 7
    Electronic Resource
    Electronic Resource
    Water loss and malate fluctuations during the day for plants in the southern Namib desert (1984)
    Springer
    Oecologia 61 (1984), S. 393-397 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The daily course of transpiration for 12 different plants growing in the southern Namib desert was investigated. Sclerophyllous species with C3 photosynthesis were the most effective water savers followed by succulents exhibiting CAM, while C3 pathway-succulents lose as much water as malacophyllous species. The different species showed either one or two peaked patterns of both transpiration and leaf conductance. With C3 plants the most common pattern is a single morning peak in leaf conductance followed by decreases in conductance over the remainder on the day. With CAM succulents leaf conductance is high in the morning, shows a pronounced midday depression and increases in the early afternoon when the malate pool is depleted, but malate consumption did not start earlier than 4 h after dawn. Seven of nine investigated C3 plants had rather high contents of malate, up to 180 μmol·g-1 dry matter. In these plants the malate content increased with increasing leaf conductance and disappeared when leaf conductance declined in the evening, indicating that malate was synthesized during photosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379641
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  • 8
    Electronic Resource
    Electronic Resource
    Availability of water controls Crassulacean acid metabolism in succulents of the Richtersveld (Namib desert, South Africa) (1985)
    Springer
    Planta 164 (1985), S. 44-55 
    Details
    ISSN: 1432-2048
    Keywords: Crassulacean acid metabolism ; Namib desert ; Water uptake ; Water stress ; Water vapour pressure deficit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Features of Crassulacean acid metabolism (CAM) were studied in a variety of different succulents in response to climatic conditions between March 1977 and October 1983 in the southern Namib desert (Richtersveld). A screening in 1977 and 1978 revealed that nearly all investigated succulents performed a CAM, but overnight accumulation of malate declined gradually with decreasing soil water potential, tissue osmotic potential, and leaf water content. This was further substantiated by an extended period of insufficient rainfall in 1979 and 1980 which damaged the evergreen CAM succulents between 80 and 100%. In most of the species still living, neither CO2-gas exchange nor diurnal acid fluctuation, indicative of CAM, could be detected unless an abundant rainfall restored both CAM features. Plants persisted in a stage of latent life. Water supply is one necessary prerequisite for CAM in the Richtersveld. But even well-watered plants with CAM were sensitive to short-term water stress caused by high water-vapour partialpressure deficit (VPD) in the night, which reduced or prevented CO2 uptake and resulted in a linear relation between overnight accumulated malate and VPD. The results do not support the opinion that, for the Namib succulents, CAM is an adaptive mechanism to water stress since long-term and short-term water stress stopped nocturnal malate synthesis, but instead lead to the conclusion that nocuturnal CO2 fixation is only performed when the water status of the plant can be improved simultaneously.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391024
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  • 9
    Electronic Resource
    Electronic Resource
    Purine alkaloid formation and CO2 gas exchange in dependence of development and of environmental factors in leaves of Coffea arabica L. (1982)
    Springer
    Planta 156 (1982), S. 295-301 
    Details
    ISSN: 1432-2048
    Keywords: Caffeine ; Coffea ; Leaf development ; Photosynthesis ; Purine alkaloids and light ; Purine alkaloids and temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the leaves of Coffea arabica L., purine alkaloid formation was estimated by analyzing the theobromine and caffeine content and by measuring the methylation rate of [2-14C]theobromine to [2-14C]caffeine in short-term experiments (6–24 h). At the same time, growth (in terms of dry weight and area), net photosynthesis (NPS), and dark respiration were determined. During leaf development, which was considered to be terminated when NPS was at a maximum (60–80 μmol g-1 s-1) and dark respiration at a minimum (5–7.5 μmol g-1 s-1), the content of theobromine and the velocity of caffeine formation were both found to decrease by a factor of more than 100. The close correlation between the theobromine content and the methylation rate is suspended when purine alkaloid formation is influenced by factors other than leaf development. Among these factors, temperature is the most effective: the velocity of caffeine biosynthesis is increased by raising the temperature and vice versa. Although the plants were well irrigated, a drastic decrease of NPS in the afternoon was observed under all environmental conditions tested. Light saturation was reached between 170–360 μmol m-2 s-1. The temperature optimum of NPS was shown to be very broad (24–33°C)m provided the adaptation time was sufficiently long.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397466
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  • 10
    Electronic Resource
    Electronic Resource
    The correlation between crassulacean acid metabolism and water uptake in Senecio medley-woodii (1985)
    Springer
    Planta 166 (1985), S. 57-66 
    Details
    ISSN: 1432-2048
    Keywords: Crassulacean acid metabolism ; Gas exchange (CO2) ; Senecio ; Transpiration ; Water uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The combination of a chamber for CO2 gas exchange with a potometric measuring arrangement allowed concomitant investigations into CO2 gas exchange, transpiration and water uptake by the roots of whole plants of Senecio medley-woodii, a species which exhibits Crassulacean acid metabolism. The water-uptake rate showed the same daily pattern as malate concentration and osmotic potential. The accumulation of organic acids resulting from nocturnal CO2 fixation enhanced the water-uptake rate from dusk to dawn. During the day the water-uptake rates decreased with decreasing organic-acid concentration. With gradually increasing water stress, CO2 dark fixation of S. medley-woodii was increased as long as water could be taken up by the roots. It was also shown that a reestablished water supply after drought caused a similar increase which in both cases ameliorated the water uptake in order to conserve a positive water balance for as long as possible. This water-uptake pattern shows that Crassulacean acid metabolism is not only a water-saving adaptation but also enhances water uptake and is directly correlated with the amelioration of the plant water status.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397386
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