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  • 1
    Monograph available for loan
    Monograph available for loan
    Life strategies of succulents in deserts : with special reference to the Namib desert (1992)
    Cambridge [u.a.] : Cambridge Univ. Press
    Details Availability
    Call number: PIK N 630-11-0269
    Description / Table of Contents: Contents: Preface ; 1. The succulent ; 2. Climate and vegetation of deserts ; 3. The Namib desert ; 4. Physiological implications ; 5. Life strategies of succulents
    Type of Medium: Monograph available for loan
    Pages: XIX, 340 S. : Ill., graph. Darst.
    ISBN: 0521244684
    Series Statement: Cambridge studies in ecology
    Location: A 18 - must be ordered
    Branch Library: PIK Library
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  • 2
    Electronic Resource
    Electronic Resource
    Interactive effects of photon fluence rates and drought on CAM-cycling in Delosperma tradescantioides (Mesembryanthemaceae) (1998)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 102 (1998), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The ability of photosynthesis and CAM to acclimate to low (220 µmol m−2 s−1; LL) and relatively high (550 µmol m−2 s−1; HL) photosynthetic photon flux densities (PPFD) was investigated in the CAM-cycling species Delosperma tradescantioides by means of CO2 gas exchange and chlorophyll fluorescence analysis. Furthermore, the influence of short-term drought on malic acid accumulation and the activity of photosystem II (PSII) was studied to assess the possible interactions between drought and the prevailing PPFD in this species. HL plants showed features of sun versus shade acclimation relative to LL plants. Nocturnal malic acid accumulation (Δ-malate) and leaf water content also tended to be higher in HL plants. Irrespective of the PPFD during growth, the weak Δ-malate doubled within 3 days of drought. Despite largely restricted CO2 uptake, photosynthetic activity as estimated from fluorescence analysis declined only ca 5%. After 7 days of drought, when plants showed CAM-idling and Δ-malate had decreased again, potential carbon assimilation was still ca 84% of that in well-watered plants and remained relatively constant throughout the day. Decarboxylation of malic acid accounted for ca 23% of potential assimilation assuming total oxidation of a maximum portion of this organic acid. Drought did not affect predawn maximum photochemical efficiency (Fv/Fm). Nonphotochemical quenching (qN) increased (24%) in response to desiccation and resulted in a more or less constant reduction state of PSII. This increase in qN resulted mainly from the change in its fast-relaxing component (qNF), while the slow component (qNS) was significant only at or above saturating PPFD in both HL and LL plants. The photon response characteristics of PSII, which differed between LL and HL plants, were unaffected by short-term drought. Photon harvesting and photon use were always adjusted to guarantee a low reduction state of PSII. Results suggest that in both LL and HL plants CAM-cycling may help to stabilize photosynthesis but to a large extent by other means than simply providing internally derived CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1998.1020119.x
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  • 3
    Electronic Resource
    Electronic Resource
    CAM variations in the leaf-succulent Delosperma tradescantioides (Mesembryanthemaceae), native to southern Africa (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 98 (1996), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides, a succulent that grows in drought-prone microenvironments in summer rainfall and all-year rainfall regions of southern Africa. When well-watered, this species exhibited Crassulacean acid metabolism (CAM)-cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low-level CAM or to CAM-idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre-stressed values within two days. Whole-shoot carbon uptake rates suggested that leaf growth had continued unabated during a short-term (≅ one week) drought. This emphasises that CAM-idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM-idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C3 gas exchanges when well-watered to water-conserving CAM-idling during drought.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1996.tb05703.x
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamic changes in leaf bulk water relations during stomatal oscillations in mangrove species. Continuous analysis using a dewpoint hygrometer (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 94 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plants of the mangrove species Pelliciera rhizophoreae and Avicennia germinans, exhibit pronounced oscillations in stomatal aperture under certain climatic conditions. During these oscillations, changes in transpirational water loss were closely followed by those in leaf water potential (ψ1) as indicated by continuous monitoring with an in situ dewpoint hygrometer. With this instrument, it was possible to measure dynamic changes in ψ1 for several days under constant conditions. Subsequently, the leaf was detached from the shoot and a pressure-volume (PV) curve was established by repeatedly weighing the leaf, still attached to the hygrometer during short interruptions of the water potential recordings. The pressure-volume relationship was then used to derive other water relations parameters from these water potential data. Thus, the procedure described herein allows a continuous analysis of the relevant components of bulk leaf water relations. Oscillations in water potential were also measured with single leaves using a pressure chamber. Water relations data obtained with these two different methods were in good agreement. In addition, osmotic potentials derived from the PV-analysis were well within the range of those determined cryoscopically using extracted cell sap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb00957.x
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  • 5
    Electronic Resource
    Electronic Resource
    Welwitschia mirabilis Hook. fil. — das Überlebenswunder der Namibwüste (1994)
    Springer
    Naturwissenschaften 81 (1994), S. 430-442 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01136642
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  • 6
    Electronic Resource
    Electronic Resource
    Welwitschia mirabilis Hook. fil. – das Überlebenswunder der Namibwüste (1994)
    Springer
    Naturwissenschaften 81 (1994), S. 430-442 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Notes: Welwitschia mirabilis are briefly outlined before a detailed description of the germination and establishment of seedlings is given. Inorganic ions, organic acids, and proline occur in high amounts in a Welwitschia leaf and exhibit typical distribution patterns. Water relations of Welwitschia, growing at three contrasting habitats of the Namib, are presented in relation to water availability in the soil and climatic constraints. A positive relationship between predawn leaf water potential and leaf growth was found. CO2 uptake and water loss measured at the three habitats showed a negligible WUE over 24 h for a whole plant. In the driest habitat, the CO2 balance of the entire leaf was negative over a period of 150 days but the leaf still grew. Utilizable biomass in the leaf was found to be high, allowing the leaf to survive even with a negative CO2 balance for at least 1 year provided water is available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01136642
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  • 7
    Electronic Resource
    Electronic Resource
    Feinstruktur und Crassulaceen-Säurestoffwechsel in Blättern von Mesembryanthemum crystallinum während natürlicher und NaCl-induzierter Alterung (1972)
    Springer
    Planta 107 (1972), S. 227-237 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary NaCl-treated young plants of Mesembryanthemum crystallinum undergo specific cytological changes which are accompanied by distinct alterations in CO2 gas exchange reactions. Prior to salt treatment mesophyll cells are quite normal. Only lomasome-like structures extrude from the cytoplasm into the vacuole. CO2 gas exchange is that of a Calvin-plant. Later on NaCl-treated plants differ from control plants in several respects. They show the CO2 gas exchange reactions typical for CAM-plants. Electron microscopy clearly shows the formation of new vacuole-like spaces just under the chloroplasts between plasmalemma and cell wall, which are mostly filled with structures similar to “Hecht'sche Fäden” of plasmolyzed cells. In many cases a large amount of vesicles and membranes can be observed in the central vacuole, at least some of which are in connection with cytoplasm and even chloroplasts. Chloroplasts themselves sometimes seem to be damaged by high concentrations of NaCl. While having a more distinct crassulacean acid metabolism, old NaCl-treated plants exhibit features of aged cells: cytoplasm becomes empty and vacuolized, stoma thylacoids are reduced. Not only the described changes in fine structure but also the altered CO2 gas exchange reactions take place when glycophytic control plants grow older, thus indicating that NaCl may accelerate the normal ageing process in Mesembryanthemum crystallinum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397938
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  • 8
    Electronic Resource
    Electronic Resource
    Solutes and succulence in southern African mistletoes (1995)
    Springer
    Trees 9 (1995), S. 303-310 
    Details
    ISSN: 1432-2285
    Keywords: Parasitic angiosperm ; Succulence ; Cations ; Organic osmolytes ; Cyclitols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The inorganic ion and organic solute composition of Tapinanthus oleifolius (Loranthaceae) and Viscum rotundifolium (Viscaceae) growing on various host trees in Namibia were investigated. Organic osmolytes accounted for 22.8–45.1% of the total solutes determined in leaves of the mistletoes parasitizing Acacia nebrownii, Catophractes alexandri, Grewia flava and Ziziphus mucronata. On other hosts (Acacia karroo, Euphorbia virosa, Salvadora persica and Tamarix usneoides) T. oleifolius showed distinct succulence with increasing leaf age, with leaves more than 3 mm thick on E. virosa. In the more succulent leaves (〉 1.1 kg H2O m−2 leaf area) organic solutes were only of minor importance. Water content per leaf area was significantly correlated with chloride content per leaf area, suggesting that succulence served as a means to keep ion concentration at a physiological tolerable level. At whole plant levels 93.7% of the total sodium of the mistletoe bush was located in leaves thicker than 1 mm for T. oleifolius parasitizing Tamarix usneoides. This pronounced sequestration of sodium in older leaves as well as the high variability of the K/Na ratio in various parts of the parasite-host system point to highly selective ion distribution processes in this association.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202493
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  • 9
    Electronic Resource
    Electronic Resource
    Physiological characteristics of geophytes in semi-arid Namaqualand, South Africa (1999)
    Springer
    Plant ecology 142 (1999), S. 121-132 
    Details
    ISSN: 1573-5052
    Keywords: Aseasonal rainfall ; Chlorophyll a fluorescence ; Gas exchange ; Leaf orientation ; Photorespiration ; Temperature optimum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Namaqualand, a semi-arid winter rainfall region of South Africa, supports an exceptional diversity of geophytic species. The survey focused on gas exchange reactions and chlorophyll a fluorescence in geophytes with different leaf orientation in relation to environmental variability. Although the above ground life cycle of geophytes can be extremely short, unlike desert annuals, they are not characterized by a high photosynthetic CO2 uptake. Maximum CO2 uptake ranged from 4 to 20 μmol CO2 m-2 s-1. Temperature optima of photosynthetic CO2 uptake were comparably low and ranged from 12 to 22 °C for eleven species tested, with only one species above 19 °C. The decrease of CO2 uptake with rising temperatures was associated with a substantial increase of photorespiration. Net photosynthesis was saturated between 500 and 900 μmol photons m-2 s-1 while electron transport through PSII was saturated at higher photon flux densities. At light intensities beyond saturation, a high variability of PSII efficiency occurred. It was highest for horizontal leaves and lowest for upright leaves. However, the maximum quantum yield of PSII (Fv/Fm)remained constant during the course of a day, regardless of leaf orientation. This indicates the absence of photoinhibitory effects and a well protected photosynthetic apparatus. Leaf orientation determined interception of solar radiation and thus leaf temperature which was highest for horizontal leaves. In conclusion, Namaqualand geophytes show photosynthetic characteristics that are well adapted to the mild and generally moist conditions during the growing season.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009870227638
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  • 10
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    Feinstruktur und Crassulaceen-Säurestoffwechsel in Blättern von Mesembryanthemum crystallinum während natürlicher und NaCl-induzierter Alterung (1972)
    Springer
    Details
    Publication Date: 1972-09-01
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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