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  • 1
    ISSN: 1432-2285
    Keywords: Forest decline ; Photosynthetic capacity ; Picea abies ; Stomatal conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Routine field determination of the parameters characterizing the activity of the photosynthetic apparatus is often difficult when attached branches of tall trees have to be used for gas exchange measurement. If severed twigs could be used, determining these parameters would be greatly facilitated. Because stomatal conductance changes when twigs or leaves are detached, CO2 assimilation is usually altered. Thus, measurements made at ambient CO2 concentration fail to accurately assess the activity of the photosynthetic apparatus because photosynthetic rates greatly depend on the supply of carbon dioxide. However, when photosynthetic carboxylation reactions are saturated by increased CO2 partial pressure in the mesophyll, CO2 assimilation rates no longer depend on instantaneous stomatal conductance, as shown by gas exchange measurements of spruce (Picea abies) twigs prior to and following detachment. Because net photosynthesis following detachment at saturating CO2 remains constant for a minimum of 15 min, photosynthetic measurements of severed twigs may be reliable. This length of time is sufficient for detaching and recutting the twig, assembling a portable minicuvette system, re-establishing steady-state conditions with the gas analyser system, and reading the data over a reasonable period of time. The method described measures the maximal photosynthetic CO2 assimilation of spruce needles of a single age-class from detached spruce twigs under the following conditions: saturating light, saturating external CO2-partial pressure, standardized temperature and air humidity in the field. The method is applicable as a routine procedure to characterize the status of the photosynthetic apparatus of spruce trees that may be damaged in the process of forest decline.
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  • 2
    ISSN: 1432-2285
    Keywords: Phyllodes ; Stomatal conductance ; Transpiration ; Water potential ; Acacia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The daily course of stomatal conductance and transpiration was monitored on each separate face of vertical phyllodes of various acacias. The selected phyllodes had a north-south orientation so that one side faced eastwards and the other westwards. The principal measurements were made on Acacia longifolia and A. melanoxylon in Portugal in late summer and autumn, and additional measurements were made on A. ligulata and A. melanoxylon in Australia. In Portugal, irrespective of soil moisture status, conductance showed on early morning maximum with a subsequent gradual decline and sometimes a subsidiary peak in the late afternoon. Maximum conductances appeared to be a function of soil moisture status, whereas the decline in conductance in the late morning and afternoon was correlated with changes in phyllode-to-air vapour pressure deficits rather than changes in phyllode water status. The relationship of transpiration to phyllode water potential did not appear to be influenced by soil moisture status, although transpiration was less in drier soils and in the afternoons, this latter factor contributing to a marked hysteresis in the relationship. The opposing faces of the phyllodes exhibited a high degree of synchrony, showing parallel stomatal opening and closing, despite their large differences in irradiance. Stomatal conductance tended to be higher on the eastern faces in the morning and lower in the afternoon. In A. longifolia the daily average of relative conductance was much the same for both faces, but in A. melanoxylon that of the eastern face was higher and was retained even when the normal orientation of the phyllodes was reversed by turning them through 180°. Synchrony must be achieved by the stomata of both sides responding to common environmental or endogenous signals which are perceived by both surfaces with equal sensitivity.
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  • 3
    ISSN: 1432-2285
    Keywords: Forest decline ; Picea abies ; Mineral deficiency ; Photosynthetic performance ; Air pollution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Damage in the older needles of Norway spruce [Picea abies (L.) Karst.] in the Fichtelgebirge (NE Bavaria, FRG) appears to result primarily from nutrient imbalances rather than from direct effects of air pollutants on the mesophyll of the needles. Support for this conclusion was obtained by altering the nutrition of older needles through the removal of terminal buds on several branches from a damaged and an undamaged spruce tree in spring. Various photosynthetic parameters, as well as the chloroplast pigment and nutrient concentrations, of 1- to 3-year-old needles on manipulated branches were compared with those of branches on which the new flush was allowed to develop during the course of the growing period. Removal of terminal buds affected only the 1-year-old needles. Elimination of the new flush resulted in a higher Ca and Mn content of the needles of the undamaged tree. This treatment also resulted in an increase of the photosynthetic capacity (under saturating light and CO2 conditions), carboxylation and light use efficiency, as well as net photosynthesis under natural conditions of the 1-year-old needles on the yellow chlorotic tree. This was accompanied by higher chlorophyll concentrations and an increase in Mg, Ca, Mn, and Zn content, and no visible signs of chlorosis developed in the experiment. By contrast, the needles of twigs in which the new flush was allowed to develop exhibited reductions in mineral content in the middle of the year. This was especially true for the elements Mg and Ca, and was accompanied by needle chlorosis and a depression of the capacity of photosynthesis. Thus it appears that there is a close relationship between the development of needle damage and nutrient imbalances in spruce. The retranslocation of elements from the 1-year-old needles to the new flush seems to play a major role in the development of needle bleaching. This approach thus supports the hypothesis described above and confirms a preliminary test with a similar experimental design, which had been conducted earlier.
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  • 4
    ISSN: 1432-2285
    Keywords: Forest decline ; Needle yellowing ; Chlorophylls ; Carotenoids ; Picea abies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary In a forest decline area (Fichtelgebirge, N.E. Bavaria, FRG), annual time courses of chloroplast pigments in both healthy and chlorotic Norway spruce were studied. The seasonal time courses of green and apparently healthy trees did not generally differ from those reported in the literature for spruce trees of other regions. Chlorophyll content increased from May to October, remained relatively constant or declined slightly during the fall and early winter, and finally decreased markedly from March to early May when pigment is at its minimum before bud break. The annual maximal chlorophyll content increased with needle age from the current year's needles to 4-yearold needles. While carotene content reached its highest concentration in August, the xanthophylls did not peak until February or March. Pigment dynamics of chlorotic trees with lower concentrations, corresponded to those of undamaged trees. Chlorophyll deficits resulted from less pigment formation as well as pigment loss during the growing period. Even when the content of total chlorophyll was low, the ratio of chlorophyll a/chlorophyll b remained almost unchanged. In conjunction with the chlorophyll reductions, a decrease in the chlorophyll/carotenoid ratio and an increase in the xanthophyll/carotene ratio occurred. The periods of needle-chlorophyll reduction did not correlate with those periods of highest concentrations of atmospheric sulphur dioxide, the main air pollutant at the stand. However, chlorophyll formation ceased in the older needle age classes of chlorotic trees when the new flush was sprouting, indicating that nutritional deficiencies affect needle yellowing more than possible direct needle damage by air pollutants.
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  • 5
    ISSN: 1432-2285
    Keywords: Canopy structure ; Quercus coccifera ; Photosynthesis ; Transpiration ; Simulation model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The structural characteristics of a diverse array of Quercus coccifera canopies were assessed and related to measured and computed light attenuation, proportion of sunlit foliage, foliage temperatures, and photosynthesis and diffusive conductance behavior in different canopy layers. A canopy model incorporating all components of shortwave and longwave radiation, and the energy balance, conductance, and CO2 and H2O exchanges of all leaf layers was developed and compared with measurements of microclimate and gas exchange in canopies in four seasons of the year. In the denser canopies with a leaf area index (LAI) greater than 5, there is little sunlit foliage and the diffuse radiation (400–700 nm) is attenuated to 5% or less of the global radiation (400–700 nm) incident on the top of the canopy. Foliage of this species is nonrandomly distributed with respect to azimuth angle, and within each canopy layer, foliage azimuth and inclination angles are correlated. A detailed version of the model which computed radiation interception and photosynthetic light harvesting according to these nonrandom distributions indicated little difference in whole-canopy gas exchange from calculations of the normal model, which assumes random azimuth orientation. The contributions of different leaf layers to canopy gas exchange are not only a function of the canopy microclimate, but also the degree to which leaves in the lower layers of the canopy exhibit more shade-leaf characteristics, such as low photosynthetic and respiratory capacity and maximal conductance. On cloudless days, the majority of the foliage in a canopy of 5.4 LAI is shaded —70%–90% depending on the time of year. Yet, the shaded foliage under these conditions is calculated to contribute only about one-third of the canopy carbon gain. This contribution is about the same as that of the upper 13% of the canopy foliage. Computed annual whole-canopy carbon gain and water use are, respectively, 60% and 100% greater for a canopy of 5 LAI than for one of 2 LAI. Canopy water-use efficiency is correspondingly less for the canopy of 5 LAI than for that of 2 LAI, but most of this difference is apparent during the cool months of the year, when moisture is more abundant.
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  • 6
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Summary Investigations inCommelina africana were aimed at checking observations, hitherto equivocal, on the ability of mesophytic higher plants to increase heat hardiness of their leaves after moderate drying. We compared the methods for the determination of viability after heat treatment which had led to ambiguous results. With determinations of the lapse of protoplasmic streaming immediately after heat treatment (Alexandrov and co-workers) it was not possible to detect an increase in heat hardiness after moderate drying. When, however, cells of leaves heated for half an hour were observed over a longer period, a faster recovery of protoplasmic streaming could be detected in dried leaves than in those heated in the saturated state. This observation is congruent with results from the estimation of macroscopic injuries during after-cultivation of leaves for a fortnight (comp.Lange and coworkers). Thus, from the ecological point of view (survival under extreme conditions) it could be explained, that not only lower plants and “xerophytic” higher plants, but also mesophytic higher plants are able to increase hardiness after loss of water. — In regard to these results some further informations on temperature hardiness behavior obtained by different methods were discussed: possibilities of adaptation to heat, changes in heat hardiness due to age and development, and also varying results on seasonal changes in frost hardiness ofHepatica nobilis (Till, Alexandrov).
    Notes: Zusammenfassung Zur Beurteilung der bisher unterschiedlichen Befunde über die Fähigkeit mesophytischer höherer Pflanzen, die Hitzeresistenz ihrer Blätter nach leichter Antrocknung zu erhöhen, wurden Untersuchungen anCommelina africana angestellt. Hierbei verglichen wir die Methoden zur Bestimmung der Vitalität nach der Hitzebehandlung, die zu den widersprüchlichen Ergebnissen geführt hatten. Bei der Bestimmung des Erlöschens der Plasmaströmung unmittelbar im Anschluß an die Hitzebehandlung (Alexandrov u. Mitarb.) war es nicht möglich, eine Erhöhung der Hitzeresistenz durch leichtes Antrocknen festzustellen. Beobachtete man aber die Zellen halbstündig erhitzter Blätter über einen längeren Zeitraum, so konnte man deutlich bei den angetrockneten Blättern eine schnellere Erholung der Plasmaströmung erkennen als bei den gesättigt erhitzten. Dieser Befund deckte sich mit den Ergebnissen, die aus der Beurteilung von makroskopisch erkennbaren Schädigungen an den Blättern während einer vierzehntägigen Nachkultur resultierten (vgl.Lange u. Mitarb.). So konnte unter ökologischen Gesichtspunkten (überleben unter extremen Bedingungen) erklärlich gemacht werden, daß nicht nur niedere Pflanzen und „xerophytische“ höhere Pflanzen, sondern auch mesophytische höhere Pflanzen zu Resistenzerhöhungen nach Wasserverlust befähigt sind. — Im Hinblick auf diese Ergebnisse wurden weitere Angaben über das Temperatur-Resistenz-verhalten bei höheren Pflanzen diskutiert, die unter Anwendung von verschiedenen Methoden gewonnen worden waren: Möglichkeiten der Hitzeresistenz-Adaptation, alters- und entwicklungsbedingte Hitzeresistenz-änderungen und auch die verschiedenen Resultate über den Jahresgang der Frostresistenz vonHepatica nobilis (Till, Alexandrov).
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  • 7
    ISSN: 1612-4677
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 30 (1989), S. 858-866 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: An operator analysis is presented that provides a unified treatment of the Schrödinger (S), Klein–Gordon (KG), and Dirac (D) equations with a Coulomb potential. The analysis uses energy shift operators that factorize an appropriate radial equation. This radial equation is based on standard results and a recent formulation of the Dirac–Coulomb problem [J. Y. Su, Phys. Rev. A 32, 3251 (1985)]. The shift operators yield energy eigenvalues and a formula that contains normalized, radial coordinate-space wave functions for the S, KG, and D equations. Formulas that contain expectation values for the S, KG, and D equations are obtained by applying the hypervirial theorem and the Hellmann–Feynman theorem to the radial equation.
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  • 9
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Measurements of the Nernst effect over a wide range of magnetic field and temperature in a nearly reversible alloy (Nb80Mo20, T c = 4.15 K, κ ∼- 4.1) are reported. Data are presented in the form of vortex transport entropy S d computed from the Nernst effect. At T = 3.5 K, values of S d (Nernst) agree well with values of S d (Ettingshausen) for fields between about 2H c1 and 0.5H c2 ,in spite of the fact that pinning forces for current-induced motion exceed those for thermally induced motion by a factor of ten at this temperature. Our measurements indicate that S d (B ≃- 0, T) 〉 S i (B ≃- 0, T) for T ≲ 0.63T C ,where S i is the entropy of formation per vortex. Values of S d (0, T) are compared with low-field theory. The pinning forces are discussed in terms of surface pinning.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Planta 100 (1971), S. 76-86 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Large areas of the lower epidermis of full-grown leaves of Polypodium vulgare (and Valerianella locusta) are normally separated from the mesophyll by an extensive subepidermal airspace. Epidermal stripes were prepared for experiments to simulate these conditions in order to investigate stomatal reactions. They were placed with their inner surface in contact with an airspace of uniformly high humidity. The outer surface was treated with air of varying degrees of humidity. The stomatal reactions were observed by microscope and the opening of the guard cells determined photographically. Treatment of the outer side of the epidermis with dry air led to a rapid closing of the stomata, whilst moist air caused opening. This induction of opening and closing movements could be repeated up to 15 times with the same stoma by changing the degree of humidity. Neighbouring groups of stomata showed different apertures according to their individual humidity conditions. The degree of aperture of the stomata depended on the water potential of the ambient air and also on the humidity conditions in the subepidermal airspace. The cause of this stomatal behaviour could lie in the “peristomatal transpiration”. In this way, the guard cells are able to function as “humidity sensors” which “measure” the difference in water potential inside and outside the leaf. Their aperture thus is controlled by their individual transpiration conditions. This controlling mechanism could be very important for the water economy of plants. They would appear to be able to reduce their transpiration through an increase in diffusion resistance of the stomata during decreasing humidity in the ambient air, without changing the water status of the whole leaf.
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