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  • 1995-1999  (15)
  • 1990-1994
  • 1980-1984  (15)
  • 1995  (15)
  • 1980  (15)
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  • 1995-1999  (15)
  • 1990-1994
  • 1980-1984  (15)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Stomatal response to environment and a possible interrelation between stomatal effects on transpiration and CO2 assimilation (1980)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 3 (1980), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract It had been hypothesized that if daily CO2 assimilation is to be maximized at a given level of daily transpiration, stomatal apertures should change during the day so that the gain ratio (∂A/∂g)/(∂E/∂g) remains constant. These partial differentials describe the sensitivity of assimilation rate (A) and transpiration rate (E) to changes in stomatal conductance (g). Experiments were conducted to determine whether stomata respond to environment in a manner which results in constant gain ratios.Gas–exchange measurements were made of the stomatal and photosynthetic responses of Vigna unguiculata L. Walp. in controlled environments. Leaf conductance to water vapour responded to step changes in temperature and humidity so that for different steady-state conditions the gain ratio remained constant on all but one day. Depletion of water in the root zone resulted in day-to-day increases in gain ratio which were correlated with decreases in maximum leaf conductance to water vapour. The significance of the results for plant adaptation and stomatal mechanisms, and methods for measuring the gain ratio, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1365-3040.ep11587040
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  • 2
    Electronic Resource
    Electronic Resource
    The concentration of xylem sap constituents in root exudate, and in sap from intact, transpiring castor bean plants (Ricinus communis L.) (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 18 (1995), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Root exudates were sampled from detopped root systems of castor bean (Ricinus communis). Different volume flux rates were imposed by changing the pneumatic pressure around the root system using a Passioura-type pressure chamber. The concentrations of cations, anions, amino acids, organic acids and abscisic acid decreased hyperbolically when flux rates increased from pure root exudation up to values typical for transpiring plants. Concentrations at low and high fluxes differed by up to 40 times (phosphate) and the ratio of substances changed by factors of up to 10. During the subsequent reduction of flux produced by lowering the pneumatic pressure in the root pressure chamber, the concentrations and ratios of substances deviated (at a given flux rate) from those found when flux was increased. The flux dependence of exudate composition cannot therefore be explained by a simple dilution mechanism. Xylem sap samples from intact, transpiring plants were collected using a Passioura-type root pressure chamber. The concentrations of the xylem sap changed diurnally. Substances could be separated into three groups: (1) calcium, magnesium and amino acid concentrations correlated well with the values expected from their concentration-flux relationships, whereas (2) the concentrations of sulphate and phosphate deviated from the expected relationships during the light phase, and (3) nitrate and potassium concentrations in intact plants varied in completely the opposite manner from those in isolated root systems. Abscisic acid concentrations in the root exudate were dependent on the extent of water use and showed strong diurnal variations in the xylem sap of intact plants even in droughtstressed plants. Calculations using root exudates overestimated export from the root system in intact plants, with the largest deviation found for proton flux (a factor of 10). We conclude that root exudate studies cannot be used as the sole basis for estimating fluxes of substances in the xylem of intact plants. Consequences for studying and modelling xylem transport in whole plants are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1995.tb00375.x
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  • 3
    Electronic Resource
    Electronic Resource
    Leaf nitrogen, photosynthesis, conductance and transpiration: scaling from leaves to canopies (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 18 (1995), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A model is presented which solves simultaneously for leaf-scale stomatal conductance, CO2 assimilation and the energy balance as a function of leaf position within canopies of well-watered vegetation. Fluxes and conductances were calculated separately for sunlit and shaded leaves. A linear dependence of photosynthetic capacity on leaf nitrogen content was assumed, while leaf nitrogen content and light intensity were assumed to decrease exponentially within canopies. Separate extinction coefficients were used for diffuse and direct beam radiation. An efficient Gaussian integration technique was used to compute fluxes and mean conductances for the canopy. The multilayer model synthesizes current knowledge of radiation penetration, leaf physiology and the physics of evaporation and provides insights into the response of whole canopies to multiple, interacting factors. The model was also used to explore sources of variation in the slopes of two simple parametric models (nitrogen- and light-use efficiency), and to set bounds on the magnitudes of the parameters.For canopies low in total N, daily assimilation rates are ∼10% lower when leaf N is distributed uniformly than when the same total N is distributed according to the exponentially decreasing profile of absorbed radiation. However, gains are negligible for plants with high N concentrations. Canopy conductance, Gc should be calculated as Gc=Aσ(fslgsl+fshgsh), where Δ is leaf area index, fsi and fsh are the fractions of sunlit and shaded leaves at each level, and gsi and gsh are the corresponding stomatal conductances. Simple addition of conductances without this weighting causes errors in transpiration calculated using the ‘big-leaf’ version of the Penman-Monteith equation. Partitioning of available energy between sensible and latent heat is very responsive to the parameter describing the sensitivity of stomata to the atmospheric humidity deficit. This parameter also affects canopy conductance, but has a relatively small impact on canopy assimilation.Simple parametric models are useful for extrapolating understanding from small to large scales, but the complexity of real ecosystems is thus subsumed in unexplained variations in parameter values. Simulations with the multilayer model show that both nitrogen- and radiation-use efficiencies depend on plant nutritional status and the diffuse component of incident radiation, causing a 2- to 3-fold variation in these efficiencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1995.tb00628.x
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  • 4
    Electronic Resource
    Electronic Resource
    Ökophysiologische Untersuchungen an Pflanzen der Namib-Wüste (1980)
    Springer
    Naturwissenschaften 67 (1980), S. 21-28 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Notes: Abstract The southern Namib desert has a vegetation cover of mainly succulent plants in which species of the Mesembryanthemaceae are predominant. Climatically this area is characterized by hot and dry days, and cool and humid nights with episodic rainfalls only in winter. In this environment a great number of species perform a crassulaceaen acid metabolism (CAM). The responses of these plants to water stress as well as the regulation of CAM in the natural habitat are described and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00424499
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  • 5
    Electronic Resource
    Electronic Resource
    Growth, photosynthesis and storage of carbohydrates and nitrogen in Phaseolus lunatus in relation to resource availability (1995)
    Springer
    Oecologia 104 (1995), S. 17-23 
    Details
    ISSN: 1432-1939
    Keywords: Carbohydrate ; Growth ; Nitrogen ; Phaseolus lunatus ; Storage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Growth, photosynthesis, and storage of nitrogen (N) and total non-structural carbohydrates (TNC) of a perennial wild type and an annual cultivar of lima bean (Phaseolus lunatus) were examined at different light intensities and N supplies. Relative growth rate and photosynthesis increased with light and N availability. N limitation enhanced biomass allocation into root rather than into shoot, while light limitation enhanced growth of leaf area. The TNC concentrations increased with light intensity and thus with photosynthesis, while the concentrations of organic N and nitrate decreased. Increasing N supply had the opposite effect. Therefore, TNC and organic N concentrations were negatively correlated (r=−0.90). Pool size of N or TNC increased with N and light availability when either resource was non-limiting, but increased little or remained constant when either resource was limiting. Storage reached a minimum when both resources were supplied at an equal rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00365557
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  • 6
    Electronic Resource
    Electronic Resource
    15N-ammonium and 15N-nitrate uptake of a 15-year-old Picea abies plantation (1995)
    Springer
    Oecologia 102 (1995), S. 361-370 
    Details
    ISSN: 1432-1939
    Keywords: Picea abies (L.) Karst ; Ammonium ; Nitrate ; 15N ; Tracer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Throughfall nitrogen of a 15-year-old Picea abies (L.) Karst. (Norway spruce) stand in the Fichtelgebirge, Germany, was labeled with either 15N-ammonium or 15N-nitrate and uptake of these two tracers was followed during two successive growing seasons (1991 and 1992). 15N-labeling (62 mg 15N m-2 under conditions of 1.5 g N m-2 atmospheric nitrogen deposition) did not increase N concentrations in plant tissues. The 15N recovery within the entire stand (including soils) was 94%±6% of the applied 15N-ammonium tracer and 100%±6% of the applied 15N-nitrate tracer during the 1st year of investigation. This decreased to 80%±24% and 83%±20%, respectively, during the 2nd year. After 11 days, the 15N tracer was detectable in 1-year-old spruce needles and leaves of understory species. After 1 month, tracer was detectable in needle litter fall. At the end of the first growing season, more than 50% of the 15N taken up by spruce was assimilated in needles, and more than 20% in twigs. The relative distribution of recovered tracer of both 15N-ammonium and 15N-nitrate was similar within the different foliage age classes (recent to 11-year-old) and other compartments of the trees. 15N enrichment generally decreased with increasing tissue age. Roots accounted for up to 20% of the recovered 15N in spruce; no enrichment could be detected in stem wood. Although 15N-ammonium and 15N-nitrate were applied in the same molar quantities (15NH 4 + : 15NO 3 - =1:1), the tracers were diluted differently in the inorganic soil N pools (15NH 4 + /NH 4 + : 15NO 3 - /NO 3 - =1:9). Therefore the measured 15N amounts retained by the vegetation do not represent the actual fluxes of ammonium and nitrate in the soil solution. Use of the molar ammonium-to-nitrate ratio of 9:1 in the soil water extract to estimate 15N uptake from inorganic N pools resulted in a 2–4 times higher ammonium than nitrate uptake by P. abies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00329803
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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Long-term effects of drought on wild and cultivated plants in the Negev desert (1980)
    Springer
    Oecologia 45 (1980), S. 19-25 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The seasonal change in diurnal patterns of net photosynthesis and daily carbon gain is studied in relation to the plant water status of the irrigated and non-irrigated naturally growing desert species Hammada scoparia, Zygophyllum dumosum, Artemisia herba-alba and Reaumuria negevensis. Comparison is made to cultivated Prunus armeniaca. Under non-irrigated natural conditions Hammada scoparia, a C4 plant, showed one-peaked flat diurnal courses of CO2 uptake which changed into a pattern of a high morning peak of CO2 uptake or slightly two-speaked curves in the late dry season. In contrast, the C3 species Zygophyllum dumosum, Artemisia herba-alba and Prunus armeniaca changed from one-peaked to distinct two-peaked patterns. At the end of the dry season, non-irrigated plants showed respiration only. Reaumuria negevensis had one-peaked curves with a low level of CO2 uptake. There is no general relation between day-time CO2 gain and pre-dawn water potential for the investigated species. In order to characterize the effect of soil drought, the CO2 gain during day-time of non-irrigated plants is expressed as a percentage of the CO2 gain of the irrigated counterparts. After an initial period of minimal drought effect, the relative day-time CO2 gain decreases almost linearly with cumulative water stress as determined by the daily addition of pre-dawn water potentials for the non-irrigated plants since the last rainfall. The slope of decrease differs from species to species. The relation of daily CO2 gain to maximal net photosynthesis is discussed. Initially, at a good plant water status, the daily CO2 gain does not decrease in proportion to the maximal photosynthetic rates as a result of stomatal control at high photosynthetic activity. At increasing water stress the daily CO2 gain decreases more than proportionally to the decrease of the maximal rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346701
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  • 10
    Electronic Resource
    Electronic Resource
    Direct turgor pressure measurements in individual leaf cells of Tradescantia virginiana (1980)
    Springer
    Planta 149 (1980), S. 445-453 
    Details
    ISSN: 1432-2048
    Keywords: Elasticity ; Hydraulic conductivity ; Leaf cells ; Tradescantia ; Turgor pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The water relations of leaves of Tradescantia virginiana were studied using the miniaturized pressure probe (Hüsken, E. Steudle, Zimmermann, 1978 Plant Physiol. 61, 158–163). Under well-watered conditions cell turgor pressures, P o, ranged from 2 to 8 bar in epidermal cells. In subsidiary cells P o was about 1.5 to 4.5 bar and in mesophyll cells about 2 to 3.5 bar. From the turgor pressure, relaxation induced in individual cells by changing the turgor pressure directly by means of the pressure probe, the half-time of water exchange was measured to be between 3 and 100 s for the epidermal, subsidiary, and mesophyll cells. The volumetric elastic modulus, ε, of individual cells was determined by changing the cell volume by a defined amount and simultaneously measuring the corresponding change in cell turgor pressure. The values for the elastic modulus for epidermal, subsidiary, and mesophyll cells are in the range of 40 to 240 bar, 30 to 200 bar, and 6 to 14 bar, respectively. Using these values, the hydraulic conductivity, L p, for the epidermal, subsidiary, and mesophyll cells is calculated from the turgor pressure relaxation process (on the basis of the thermodynamics of irreversible processes) to be between 1 and 55·10-7 cm s-1 bar-1. The data for the volumetric elastic modulus of epidermal and subsidiary cells indicate that the corresponding elastic modulus for the guard cells should be considerably lower due to the large volume changes of these cells during opening or closing. Recalculation of experimental data obtained by K. Raschke (1979, Encycl. Plant Physiol. N.S., vol. 7, pp 383–441) on epidermal strips of Vicia faba indicates that the elastic modulus of guard cells of V. faba is in the order of 40–80 bar for closed stomata. However, with increasing stomatal opening, i.e., increasing guard cell volume, ε decreases. Therefore, in our opinion Raschke's results would indicate a relationship between guard cell volume and ε which would be inverse to that for plant cells known in the literature. ε assumes values between 20–40 bar when the guard cell colume is soubled.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385746
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