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  • 1
    Electronic Resource
    Electronic Resource
    Light-flecks cause non-uniform stomatal opening – studies with special emphasis on Fagus sylvatica L. (1999)
    Springer
    Trees 14 (1999), S. 130-144 
    Details
    ISSN: 0931-1890
    Keywords: Key words Half-shade leaves ; Photosynthetic induction ; Shade leaves ; Stomatal patchiness ; Water infiltration method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The appearance of stomatal patchiness in response to rapid (seconds) changes in light has been studied in European beech, Fagus sylvatica L., and, by comparison, in a further 17 different woody species from the understorey of a European beech forest, using a simple water infiltration method. Water infiltrated areoles indicate open stomata. Since infiltration changes optical characteristics of a leaf section it can be analysed by photography, computer-aided image analysis and by weighing. For F. sylvatica clear differences were found between infiltration of cotyledons (no patchy pattern) and any other leaf type. Despite identical cultivation, leaves of the same type and age from different individual plants responded differently to application of 30 s of light after darkness. In contrast, the patchiness patterns were very similar for leaves of the same type originating from the same plant. Infiltration patterns after a light-fleck, observed on different leaves as a series of momentary clusters, probably indicate waves of opening stomata moving across the leaf blade. During and after a 30 s light-fleck infiltration increased and it continued to increase in the dark up to 10 min, indicating increasing stomatal opening over that period. In general, shade leaves became more infiltrated (by weight) than half-shade or sun leaves, due to larger intercellular air spaces. All species, without exception, showed patchy infiltration and, thus, non-uniform stomatal opening. Measuring leaf gas exchange (as ”quasi-steady states” using a fast responding system) during photosynthetic induction resulted in very similar CO2 responses of net photosynthesis (A/c i) as in the true steady state, proving that, in shade and half-shade leaves, the presence of stomatal patchiness does not necessarily affect the calculation of intercellular CO2 concentrations. Causes and consequences of stomatal patchiness are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009759
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  • 2
    Electronic Resource
    Electronic Resource
    Simulation of photosynthetic plasticity in response to highly fluctuating light: an empirical model integrating dynamic photosynthetic induction and capacity (1999)
    Springer
    Trees 14 (1999), S. 145-160 
    Details
    ISSN: 0931-1890
    Keywords: Key words Canopy photosynthesis ; Dynamic photosynthesis simulation ; Lightfleck ; Photosynthetic capacity ; Photosynthetic induction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  An empirical model was developed to simulate photosynthetic responses of leaves to highly fluctuating light, with a special focus on the functional role of photosynthetic induction and capacity. Based on diurnal courses of light as input data, which were recorded at natural plant sites, we applied this model to simulate the corresponding course of net photosynthesis (output data) for leaves of two neotropical tree species. All six model input parameters (leaf-specific) were obtained via measurements of leaf gas exchange. The model was tested for leaves in their natural environments, characterized by frequent light-flecks. We compared measured carbon gains with computed ones, using a standard steady-state and our induction model. Simulation runs with the steady-state model can result in an immense overestimation of the true situation, by 13.4% at open sites [pioneer species Heliocarpus appendiculatus (Turczaninow)] and by 86.5% at low light environments of the understorey [mid to late successional species Billia colombiana (Planchon and Lindley)]. These significant overestimations, particularly in the understorey, are mainly the consequence of neglecting a dynamic photosynthetic induction under fluctuating light conditions. The model presented here resulted in clearly improved predictions; in open and understorey sites the true carbon gain of leaves was computed with a mean error of less than 7%. As most leaves at natural plant sites are exposed to light environments allowing for dynamic rather than steady-state CO2 assimilation, the significance of such induction models is evident and is discussed in relation to scaling-up from leaf to canopy and to the whole plant indicating a large potential for errors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004680050219
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  • 3
    Electronic Resource
    Electronic Resource
    Rain, winds and haze during the Huygens probe's descent to Titan's surface (2005)
    [s.l.] : Nature Publishing Group
    Nature 438 (2005), S. 765-778 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The irreversible conversion of methane into higher hydrocarbons in Titan's stratosphere implies a surface or subsurface methane reservoir. Recent measurements from the cameras aboard the Cassini orbiter fail to see a global reservoir, but the methane and smog in Titan's atmosphere impedes ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature04126
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  • 4
    Electronic Resource
    Electronic Resource
    Hydraulic flow characteristics in the lignotuberous mallee Eucalyptus behriana F. Muell. in the field (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 10 (1987), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The lignotuberous mallee Eucalyptus behriana F. Muell, had much lower predawn leaf water potentials (not higher than – 1.2MPa) than other eucalypts (as high as – 0.2MPa), even after extended rain. This led to the expectation that the lignotuber of E. behriana might have specific hydraulic characteristics. Keeping the soil around partially defoliated mallces for several days underwater did not raise the water status above the maximum leaf water potential observed under natural conditions. Digging a plant out and placing its roots in water after removal of the soil rapidly increased the water status to a level consistant with other eucalypts. This indicated that the major impedance to water uptake was a component of the soil rather than in the roots or in the lignotuber.Some of the individual mallces had only two major stems or branches. One stem or branch was kept covered throughout the experiments to prevent transpiration. The other stem was subjected to a variety of different conditions in order to modify water loss from it. The transpiring branch affected the water status of the non-transpiring plant parts. Hydraulic resistances in the shoot and root/lignotuber were determined from differences in the leaf water potential of covered and uncovered branches, at high water flow rates through the plant. Resistances in branches, including the liquid phase component of the leaf, were significantly larger than in root or lignotuber.The total plant hydraulic resistance of E. behriana was similar to that of other eucalypts, such as E. pauciflora Sieb. ex Spreng. or E. delegatensis R. T. Bak., even though its growth form was different and its natural leaf water potentials were much lower. An osmotic adjustment at the leaf level was observed in the mallee, keeping its bulk leaf turgor in the same range as compared to the other eucalypt species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1987.tb02076.x
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  • 5
    Electronic Resource
    Electronic Resource
    Critical plane approach for the assessment of the fatigue behaviour of welded aluminium under multiaxial loading (2003)
    Oxford, UK : Blackwell Science, Ltd
    Fatigue & fracture of engineering materials & structures 26 (2003), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Multiaxial stress states occur in many welded constructions like chemical plants, railway carriages and frames of trucks. Those stresses can have constant and changing principal stress directions, depending on the loading mode. Latest research results on welded steel joints show a loss of fatigue life for changing principal stress directions simulated by out-of-phase bending and torsion compared to constant directions given by in-phase loading. However, aluminium welds reveal no influence of changing principal directions on fatigue life compared to multiaxial loading with constant principal stress directions. This behaviour is not predictable by any conventional hypothesis. A hypothesis on the basis of local normal and shear stresses in the critical plane has been developed and applied to aluminium weldings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-2695.2003.00674.x
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  • 6
    Electronic Resource
    Electronic Resource
    Multiaxial fatigue of welded joints under constant and variable amplitude loadings (2001)
    Oxford, UK : Blackwell Science Ltd
    Fatigue & fracture of engineering materials & structures 24 (2001), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Flange-tube joints from fine grained steel StE 460 with unmachined welds were investigated under biaxial constant and variable amplitude loading (bending and torsion) in the range of 103 to 5 × 106 cycles to crack initiation and break-through, respectively. In order not to interfere with residual stresses they were relieved by a heat treatment. In-phase loading can be treated fairly well using the conventional hypotheses (von Mises or Tresca) on the basis of nominal, structural or local strains or stresses. But the influence of out-of-phase loading on fatigue life is severely overestimated if conventional hypotheses are used. However, the hypothesis of the effective equivalent stress that is introduced leads to fairly good predictions for constant as well as for random variable amplitude loads. Therefore, the knowledge of local strains or stresses is necessary. They are determined by boundary element analyses that are dependent on weld geometry. This hypothesis considers the fatigue-life-reducing influence of out-of-phase loading by taking into account the interaction of local shear stresses acting in different surface planes of the material. Further, size effects resulting from weld geometry and loading mode were included. Damage accumulation under a Gaussian spectrum can be assessed for in- and out-of-phase combined bending and torsion using an allowable damage sum of 0.35.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-2695.2001.00393.x
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  • 7
    Electronic Resource
    Electronic Resource
    The influence of CO2 enrichment, phosphorus deficiency and water stress on the growth, conductance and water use of Pinus radiata D. Don (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. Seedlings of Pinus radiata D. Don were grown in growth chambers for 22 weeks with two levels of phosphorus, under either well-watered or water-stressed conditions at CO2 concentrations of either 330 or 660mm3 dm−3. Plant growth, water use efficiency and conductance were measured and the relationship between these and needle photosynthetic capacity, water use efficiency and conductance was determined by gas exchange at week 22. Phosphorus deficiency decreased growth and foliar surface area at both CO2concentrations; however, it only reduced the maximum photosynthetic rates of the needles at 660 mm3 CO2 dm−3 (plants grown and measured at the same CO2 concentration). Water stress reduced growth and foliar surface area at both CO2 concentrations. Increases in needle photosynthetic rates appeared to be partly responsible for the increased growth at high CO2 where phosphorus was adequate. This effect was amplified by accompanying increases in needle production. Phosphorus deficiency inhibited these responses because it severely impaired needle photosynthetic function. The relative increase in growth in response to high CO2 was higher in the periodically water-stressed plants. This was not due to the maintenance of cell volume during drought. Plant water use efficiency was increased by CO2 enrichment due to an increase in dry weight rather than a decrease in shoot conductance and, therefore, transpirational water loss. Changes in needle conductance and water use efficiency in response to high CO2 were generally in the same direction as those at the whole plant level. If the atmospheric CO2 level reaches the predicted concentration of 660 mm3 dm−3 by the end of next Century, then the growth of P. radiata will only be increased in areas where phosphorus nutrition is adequate. Growth will be increased in drought-affected regions but total water use is unlikely to be reduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1365-3040.ep11604890
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  • 8
    Electronic Resource
    Electronic Resource
    A field portable system for the measurement of gas exchange of leaves under natural and controlled conditions: examples with field-grown Eucalyptus pauciflora Sieb. ex Spreng. ssp. pauciflora, E. behriana F. Muell. and Pinus radiata R. Don. (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 10 (1987), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A field portable system is described which measures the response of gas exchange of one leaf to changes in environmental parameters under controlled conditions, and which simultaneously measures the gas exchange of another leaf as the climatic parameters vary naturally. The system consists of two independently operating cuvettes. It enables detailed studies of photosynthesis and stomata/transpiration of leaves attached to the plant in their natural position. It provides control of temperature, humidity, CO2 and oxygen concentration (or, alternatively, of other gases) as well as of light. Infrared gas analyzers for CO2 and H2O are used which allow similar time constants for the measurement of the two gases.Examples of a diurnal course of gas exchange of a leaf in its natural exposition and of experiments with steady-state responses of gas exchange are presented. In Eucalyptus pauciflora Sieb. ex Spreng. ssp. pauciflora, a set of response curves of CO, assimilation (A) to CO2, as measured at various leaf temperatures and light levels, shows carboxylation efficiency to be light saturated at the lower photon irradiances the lower the leaf temperature is. Carboxylation efficiency is maximal at 25°C. At ambient CO, partial pressure stomata open in a way that CO2 assimilation occurs at a rate found within the curvature region of the CO2 response function of A. The light-independent CO2 compensation point as a function of temperature is presented.Applying a combined heat/low humidity pulse (15 or 60 min) on leaves of Eucalyptus behriana F. Muell. or Pinus radiata R. Don, respectively, leads to a lower level of intercellular carbon dioxide partial pressure (Ci) during the decline in A and leaf conductance to water vapour (g). A lower Ci level is maintained during recovery of A and g, A almost reaching the pre-pulse level but not g. The existence of an after-effect indicates that the response to the combined high temperature/low humidity pulse is a multi-step process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1365-3040.ep11603690
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of day-to-day changes in root temperature on leaf conductance to water vapour and CO2 assimilation rates of Vigna unguiculata L. Walp. (1982)
    Springer
    Oecologia 52 (1982), S. 116-120 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Leaf gas exchange of Vigna unguiculata was influenced by short-term (day-to-day) changes in soil temperature and the response depended upon the aerial environment. When aerial conditions were constant at 30° C leaf temperature, high air humidity and moderate quantum flux, CO2 assimilation rate and leaf conductance increased with increases in soil temperature from 20 to 35° C, and this response was reversible. Decreases in CO2 assimilation rate and leaf conductance were observed at root temperatures above 30° C when root temperatures were increased from 20° C to 40° C and when air humidity was decreased in steps during the day. In contrast, varying soil temperatures between 20 to 35° C had no influence on gas exchange when shoots were subjected to a wide range of temperatures during each day. The gain ratio ∂A/τE remained constant at different air humidities when root temperature was less than or equal to 30° C indicating optimal gas exchange regulation, but changed with humidity at higher root temperatures. Leaf conductance responded independently from leaf water potential which remained relatively constant during individual experiments. The results indicate that plant responses to high root temperatures may have relevance to plant performance in semi-arid environments. They also illustrate the importance of controlling soil temperatures when studying the responses of potted plants in controlled aerial environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349019
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  • 10
    Electronic Resource
    Electronic Resource
    Diurnal variations of light-saturated CO2 assimilation and intercellular carbon dioxide concentration are not related to leaf water potential (1986)
    Springer
    Oecologia 69 (1986), S. 477-480 
    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/BF00377072
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