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  • 1980-1984  (24)
  • 1
    Electronic Resource
    Electronic Resource
    Changes in photosynthetic capacity, carboxylation efficiency, and CO2 compensation point associated with midday stomatal closure and midday depression of net CO2 exchange of leaves of Quercus suber (1984)
    Springer
    Planta 162 (1984), S. 193-203 
    Details
    ISSN: 1432-2048
    Keywords: Carboxylation efficiency ; Compensation point (CO2) ; Photosynthesis (temperature, humidity) ; Quercus ; Sclerophyll
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The carbon-dioxide response of photosynthesis of leaves of Quercus suber, a sclerophyllous species of the European Mediterranean region, was studied as a function of time of day at the end of the summer dry season in the natural habitat. To examine the response experimentally, a “standard” time course for temperature and humidity, which resembled natural conditions, was imposed on the leaves, and the CO2 pressure external to the leaves on subsequent days was varied. The particular temperature and humidity conditions chosen were those which elicited a strong stomatal closure at midday and the simultaneous depression of net CO2 uptake. Midday depression of CO2 uptake is the result of i) a decrease in CO2-saturated photosynthetic capacity after light saturation is reached in the early morning, ii) a decrease in the initial slope of the CO2 response curve (carboxylation efficiency), and iii) a substantial increase in the CO2 compensation point caused by an increase in leaf temperature and a decrease in humidity. As a consequence of the changes in photosynthesis, the internal leaf CO2 pressure remained essentially constant despite stomatal closure. The effects on capacity, slope, and compensation point were reversed by lowering the temperature and increasing the humidity in the afternoon. Constant internal CO2 may aid in minimizing photoinhibition during stomatal closure at midday. The results are discussed in terms of possible temperature, humidity, and hormonal effects on photosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397440
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  • 2
    Electronic Resource
    Electronic Resource
    Midday stomatal closure in Arbutus unedo leaves in a natural macchia and under simulated habitat conditions in an environmental chamber (1980)
    Springer
    Oecologia 47 (1980), S. 365-367 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00398530
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  • 3
    Electronic Resource
    Electronic Resource
    Variation in carbon isotope ratios of Sempervivoideae species from different habitats of Teneriffe in the spring (1982)
    Springer
    Oecologia 55 (1982), S. 217-224 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary According to carbon isotope ratios, species of the Sempervivoideae from Teneriffe show in general a tendency for increased participation of dark CO2 fixation via PEP-carboxylase in total carbon fixation as habitats become drier and warmer. Certain species are found in cool moist habitats and exhibit C3-like δ13C values. Other species occur in warm dry habitats and exhibit δ13C values which indicate strong Crassulacean Acid Metabolism. A third group of species shows intermediate δ13C values which are more C3-like in cool moist habitats and which indicate increased dark fixation in warmer and drier situations. Included in this group is Aeonium holochrysum, which of the Sempervivoideae of Teneriffe is thought to be most closely related to the common ancestor (Lems 1960). Comparison of CO2 gas exchange of several species under identical environmental conditions reveals differences among species in the ability to regulate CO2 fixation in the light and in the dark which may have arisen in the process of adaptive radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00384490
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  • 4
    Electronic Resource
    Electronic Resource
    A portable steady-state porometer for measuring the carbon dioxide and water vapour exchanges of leaves under natural conditions (1982)
    Springer
    Oecologia 53 (1982), S. 141-145 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A portable porometer is described for measuring the steady-state CO2 and H2O exchange rates of leaves under natural conditions. The porometer has an open gas exchange system which monitors the differences in concentrations of CO2 and H2O entering and leaving a cuvette which is clamped on or around leaves. The cuvette is designed to maintain ambient air temperature and humidity around the leaf. This instrument may also be used to determine CO2 response curves in the field. Examples of diurnal courses are presented for attached leaves of different species having high and low rates of CO2 exchange.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00545656
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  • 5
    Electronic Resource
    Electronic Resource
    The control by atmospheric factors and water stress of midday stomatal closure in Arbutus unedo growing in a natural macchia (1982)
    Springer
    Oecologia 55 (1982), S. 165-169 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Midday closure of stomata of well-watered (ψ between-10 and-25 bar) or moderately stressed (ψ between-25 and-35 bar) Arbutus unedo plants occurs when midday leaf temperatures increase above 30°C and vapor pressure difference between leaf air spaces and the external air increases above approximately 30 mbar/bar. Moderate water stress decreases maximum conductance and may result in greater sensitivity to high leaf temperature and vapor pressure dificit, which results in earlier closure and later reopening of stomata. Severe water stress (ψ of-50 bar) changes the form of the daily pattern observed for leaf conductance. A single morning peak in conductance occurs followed by decrease in conductance over the remainder of the day. Morning fog in Portugal during the dry season may facilitate stomatal opening and may allow improvement of carbon balances of the leaves for short periods, but contributes little to improvement of plant water balances over the longer term.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00384483
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  • 6
    Electronic Resource
    Electronic Resource
    Development of a photosynthesis model with an emphasis on ecological applications (1980)
    Springer
    Oecologia 45 (1980), S. 147-155 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A physiologically based steady-state model of whole leaf photosynthesis (WHOLEPHOT) is used to describe net photosynthesis daily time courses in Prunus armeniaca. Net photosynthesis rates are calculated in response to incident light intensity, leaf temperature, air carbon dioxide concentration, and leaf diffusion resistance measured at five minute intervals. The steady-state calculations closely approximate the observed net photosynthesis rates for a broad range of weather conditions and leaf stomatal behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346453
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  • 7
    Electronic Resource
    Electronic Resource
    Moisture content and CO2 exchange of lichens. II. Depression of net photosynthesis in Ramalina maciformis at high water content is caused by increased thallus carbon dioxide diffusion resistance (1981)
    Springer
    Oecologia 51 (1981), S. 426-429 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Thalli of Ramalina maciformis were moistened to their maximal water holding capacity, thus, simulating actual conditions following a heavy rainfall. Time courses of net photosynthesis at 17° C and 750 μE m-2 s-1 light intensity (PAR) were obtained during drying of the thalli. At ambient CO2 concentrations from 200 to 1,000 ppm, CO2 uptake of the moist lichens was depressed at high water content. After a certain water loss, net photosynthesis increased to a maximal value and decreased again with further drying of the thalli. The degree of initial depression of photosynthesis decreased with increasing ambient CO2 concentration, and it was fully absent at 1,600 ppm ambient CO2. Under these conditions of CO2 saturation, net photosynthesis remained constant at maximum for many hours and decreased only when substantial amounts of water had been lost. We conclude that the carboxylation capacity of the lichen is not affected by high contents of liquid water. Therefore, the depression of CO2 uptake of the water saturated lichen at lower (e.g. natural) ambient CO2 must be due exclusively to increased resistance to CO2 diffusion from the external air to the sites of carboxylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00540917
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  • 8
    Electronic Resource
    Electronic Resource
    The diurnal time course of net photosynthesis of soybean leaves: Analysis with a physiologically based steady-state photosynthesis model (1980)
    Springer
    Oecologia 46 (1980), S. 314-321 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A physiologically based steady-state model of whole leaf photosynthesis (WHOLEPHOT) is used to analyze observed net photosynthesis daily time courses of soybean, Glycine max (L.) Merr., leaves. Observations during two time periods of the 1978 growing season are analyzed and compared. After adjustment of the model for soybean, net photosynthesis rates are calculated with the model in response to measured incident light intensity, leaf temperature, air carbon dioxide concentration, and leaf diffusion resistance. The steady-state calculations closely approximate observed net photosynthesis. Results of the comparison reveal a decrease in photosynthetic capacity in leaves sampled during the second time period, which is associated with decreasing ability of leaves to respond to light intensity and internal air space carbon dioxide concentration, increasing mesophyll resistance, and increasing stomatal resistance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346258
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  • 9
    Electronic Resource
    Electronic Resource
    Determination of leaf heat resistance: comparative investigation of chlorophyll fluorescence changes and tissue necrosis methods (1984)
    Springer
    Oecologia 63 (1984), S. 256-262 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Heat tolerance limits for a variety of vascular plant leaves were determined both with the conventional post-culture necrosis method and by measurements of the heat-induced increase in chlorophyll fluorescence (F-T curves). The reliability of the fluorescence test was improved with the addition of far-red background light which counteracts dark reduction of the Photosystem II acceptor pool by heat-stimulated endogenous electron donors. This was of particular importance in the case of xeromorphic leaves in which the diffusion barrier for oxygen is high. A satisfactory correlation was found between T L50, the temperature at which a 30 min exposure results in 50% necrotic leaf area following post culture, and the critical temperature, T c ,the temperature at which the dark fluorescence level begins to increase during slow heating of a leaf sample at a rate of 0.7 K min-1, in the fluorescence test. The correlation can be described by a linear function, T L50=1.12 T c -5.37,with a correlation coefficient, r=0.87. Maximal deviation of the regression line from the line T L50=T c was 1.2 K, with 22 determinations for leaves with widely varying heat tolerance limits. This shows that heat-induced fluorescence changes within the thylakoid membrane may be connected with the irreversible leaf tissue damage which occurs following prolonged exposure to high temperature. On the basis of the heat dosage equation of Lepeschkin, a more general expression can be obtained which allows calculation of the accumulated heat dosage under the experimental conditions of the standard fluorescence test (slow heating, 0.7 K min-1). Such calculations reveal that for a given species the ‘fraction of critical dosage’ begins to increase, i.e. accumulating heat reaches an injurious level, at a temperature which approximately coincides both with T L50, obtained with the necrosis method, and with T c ,the critical temperature derived from the fluorescence test. Hence, the increase in fraction of critical dosage and the rise in chlorophyll fluorescence seem to concur. It is concluded that the fluorescence assay provides a rapid and reliable means of determining the heat tolerance limit of leaf tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379886
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  • 10
    Electronic Resource
    Electronic Resource
    Long-term effects of drought on wild and cultivated plants in the Negev desert (1980)
    Springer
    Oecologia 45 (1980), S. 11-18 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The relation between daily maximal rates of net photosynthesis and plant water status was studied during a dry season on irrigated and non-irrigated, naturally growing, perennial wild plants. Species were examined which differ in phenology, leaf anatomy and morphology: Hammada scoparia, Artemisia herba-alba, Zygophyllum dumosum, and Reaumuria negevensis. Prumus armeniaca which was growing in the run-off farm at Avdat and which has mosomorphic leaves was included in the comparison. All plants differed in their seasonal change in plant water status, and in their seasonal change in daily maximal net photosynthesis. Rates of CO2 uptake were not uniquely related to simultanously measured leaf water potentials. Daily maximal rates of net photosynthesis of non-irrigated plants, and the difference between maximal CO2 uptake of irrigated and non-irrigated plants were examined in relation to pre-dawn water potential. Maximal net photosynthesis rates decreased very rapidly with decrease in pre-dawn water potential or, for Hammada scoparia, they decreased even with a constant level of pre-dawn water potential. Consequently, it was considered necessary to include both time and water potential in a parameter “bar day” describing the accumulated drought stress of the plants. All species showed the same relation between relative maximal net photosynthesis and drought experience as determined by cumulative daily addition of pre-dawn water potentials for the non-irrigated plants since the last rain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346700
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