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  • 1
    Electronic Resource
    Electronic Resource
    Influence of nutrient versus water supply on hydraulic architecture and water balance in Pinus taeda (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We investigated the hydraulic consequences of a major decrease in root-to-leaf area ratio (AR:AL) caused by nutrient amendments to 15-year-old Pinus taeda L. stands on sandy soil. In theory, such a reduction in AR:AL should compromise the trees’ ability to extract water from drying sand. Under equally high soil moisture, canopy stomatal conductance (GS) of fertilized trees (F) was 50% that of irrigated/fertilized trees (IF), irrigated trees (I), and untreated control trees (C). As predicted from theory, F trees also decreased their stomatal sensitivity to vapour pressure deficit by 50%. The lower GS in F was associated with 50% reduction in leaf-specific hydraulic conductance (KL) compared with other treatments. The lower KL in F was in turn a result of a higher leaf area per sapwood area and a lower specific conductivity (conducting efficiency) of the plant and its root xylem. The root xylem of F trees was also 50% more resistant to cavitation than the other treatments. A transport model predicted that the lower AR:AL in IF trees resulted in a considerably restricted ability to extract water during drought. However, this deficiency was not exposed because irrigation minimized drought. In contrast, the lower AR:AL in F trees caused only a limited restriction in water extraction during drought owing to the more cavitation resistant root xylem in this treatment. In both fertilized treatments, approximate safety margins from predicted hydraulic failure were minimal suggesting increased vulnerability to drought-induced dieback compared with non-fertilized trees. However, IF trees are likely to be so affected even under a mild drought if irrigation is withheld.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00625.x
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of tree height on crown level stomatal conductance (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Variation in stomatal conductance is typically explained in relation to environmental conditions. However, tree height may also contribute to the variability in mean stomatal conductance. Mean canopy stomatal conductance of individual tree crowns (GSi) was estimated using sap flux measurements in Fagus sylvatica L., and the hypothesis that GSi decreases with tree height was tested. Over 13 d of the growing season during which soil moisture was not limiting, GSi decreased linearly with the natural logarithm of vapour pressure deficit (D), and increased exponentially to saturation with photosynthetic photon flux density (Qo). Under conditions of D= 1 kPa and saturating Qo, GSi decreased by approximately 60% with 30 m increase in tree height. Over the same range in height, sapwood-to-leaf area ratio (AS:AL) doubled. A simple hydraulic model explained the variation in GSi based on an inverse relationship with height, and a linear relationship with AS:AL. Thus, in F. sylvatica, adjustments in AS:AL partially compensate for the negative effect of increased flow-path length on leaf conductance. Furthermore, because stomata with low conductance are less sensitive to D, gas exchange of tall trees is reduced less by high D. Despite these compensations, decreasing hydraulic conductance with tree height in F. sylvatica reduces carbon uptake through a corresponding decrease in stomatal conductance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00553.x
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature influence on Arctic charr (Salvelinus alpinus L.) antibody response to a cellular antigen (2000)
    Springer
    Polar biology 23 (2000), S. 231-235 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to elucidate the immune responses of Arctic charr in relation to temperature, groups were acclimated to a moderate (9°C) and a cold temperature regime (4°C), as well as subjected to a temperature decrease (from 9 to 4°C) immediately prior to an immunization with sheep red blood cells. The charr kept at 9°C responded with increased primary and secondary antibody titres, as seen by direct haemagglutination, while fish at 4°C, as well as the fish subjected to a temperature reduction, displayed lower and lowest antibody titres, respectively, and only after a second immunization. It is concluded that Arctic charr can respond to a cellular antigen with a humoral immune response typical for other teleosts, but that the immune response is delayed and diminished at low temperatures. This temperature-induced immune suppression is intensified if the fish have not been acclimated to cold water prior to immunization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003000050439
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of soil porosity on water use in Pinus taeda (2000)
    Springer
    Oecologia 124 (2000), S. 495-505 
    Details
    ISSN: 1432-1939
    Keywords: Key words  Pinus taeda ; Xylem cavitation ; Soil water transport ; Root-shoot relations ; Stomatal regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We analyzed the hydraulic constraints imposed on water uptake from soils of different porosities in loblolly pine (Pinus taeda L.) by comparing genetically related and even-aged plantations growing in loam versus sand soil. Water use was evaluated relative to the maximum transpiration rate (E crit) allowed by the soil-leaf continuum. We expected that trees on both soils would approach E crit during drought. Trees in sand, however, should face greater drought limitation because of steeply declining hydraulic conductivity in sand at high soil water potential (Ψ S). Transport considerations suggest that trees in sand should have higher root to leaf area ratios (A R:A L), less negative leaf xylem pressure (Ψ L), and be more vulnerable to xylem cavitation than trees in loam. The A R:A L was greater in sand versus loam (9.8 vs 1.7, respectively). This adjustment maintained about 86% of the water extraction potential for both soils. Trees in sand were more deeply rooted (〉1.9 m) than in loam (95% of roots 〈0.2 m), allowing them to shift water uptake to deeper layers during drought and avoid hydraulic failure. Midday Ψ L was constant for days of high evaporative demand, but was less negative in sand (–1.6 MPa) versus loam (–2.1 MPa). Xylem was more vulnerable to cavitation in sand versus loam trees. Roots in both soils were more vulnerable than stems, and experienced the greatest predicted loss of conductivity during drought. Trees on both soils approached E crit during drought, but at much higher Ψ S in sand (〈–0.4 MPa) than in loam (〈–1.0 MPa). Results suggest considerable phenotypic plasticity in water use traits for P. taeda which are adaptive to differences in soil porosity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008875
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  • 5
    Electronic Resource
    Electronic Resource
    Pyrazinamide inhibits the eukaryotic-like fatty acid synthetase I (FASI) of Mycobacterium tuberculosis (2000)
    [s.l.] : Nature America Inc.
    Nature medicine 6 (2000), S. 1043-1047 
    Details
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Tuberculosis treatment is shortened to six months by the indispensable addition of pyrazinamide (PZA) to the drug regimen that includes isoniazid and rifampin. PZA is a pro-drug of pyrazinoic acid (POA) (ref. 3), whose target of action has never been identified. Although PZA is active only against ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/79558
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  • 6
    Electronic Resource
    Electronic Resource
    Modelling Vegetation-Atmosphere Co2 Exchange By A Coupled Eulerian-Langrangian Approach (2000)
    Springer
    Boundary layer meteorology 95 (2000), S. 91-122 
    Details
    ISSN: 1573-1472
    Keywords: Canopy turbulence ; Lagrangian stochastic model ; Turbulence closure ; Canopy photosynthesis ; Carbon dioxide ; Radiation attenuation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A Eulerian-Lagrangian canopy microclimate model wasdeveloped with the aim of discerning physical frombiophysical controls of CO2 and H2O fluxes. The model couples radiation attenuation with mass,energy, and momentum exchange at different canopylevels. A unique feature of the model is its abilityto combine higher order Eulerian closure approachesthat compute velocity statistics with Lagrangianscalar dispersion approaches within the canopy volume. Explicit accounting for within-canopy CO2,H2O, and heat storage is resolved by consideringnon-steadiness in mean scalar concentration andtemperature. A seven-day experiment was conducted inAugust 1998 to investigate whether the proposedmodel can reproduce temporal evolution of scalar(CO2, H2O and heat) fluxes, sources andsinks, and concentration profiles within and above auniform 15-year old pine forest. The modelreproduced well the measured depth-averaged canopy surfacetemperature, CO2 and H2O concentrationprofiles within the canopy volume, CO2 storageflux, net radiation above the canopy, and heat andmass fluxes above the canopy, as well as the velocitystatistics near the canopy-atmosphere interface. Implications for scaling measured leaf-levelbiophysical functions to ecosystem scale are alsodiscussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002473906184
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  • 7
    Electronic Resource
    Electronic Resource
    Halocins: are they involved in the competition between halobacteria in saltern ponds? (2000)
    Springer
    Extremophiles 4 (2000), S. 35-41 
    Details
    ISSN: 1433-4909
    Keywords: Key words Halocins ; Halobacteria ; Salterns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Many representatives of the family Halobacteriaceae ("halobacteria") excrete halophilic bacteriocins (halocins) that inhibit the growth of other halobacteria. In spite of the fact that halocin production is widespread among the Halobacteriaceae, no information is available on their ecological significance. To test whether halocins may play a role in the interspecies competition between dif-ferent types of halobacteria in saltern crystallizer ponds inhabited by dense communities of these red halophiles, we assayed for halocins active against a variety of halobacteria in salterns from different locations worldwide. Detection of halocin activity was based on the inhibition of growth of indicator organisms on agar plates, the decreased incorporation of radiolabeled substrates, and microscopic examinations. No halocin activity was detected in any of the brines examined, in spite of the fact that halocin production was demonstrated in cultures of most microorganisms isolated from these brines. Thus, the contribution of halocins in the competition between different halobacteria in hypersaline aquatic environments is probably negligible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007920050005
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  • 8
    Electronic Resource
    Electronic Resource
    Comparisons of the polar lipid and pigment profiles of two solar salterns located in Newark, California, U.S.A., and Eilat, Israel (2000)
    Springer
    Extremophiles 4 (2000), S. 259-265 
    Details
    ISSN: 1433-4909
    Keywords: Key words Solar salterns ; Halophilic Archaea ; Halophilic Bacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The whole community pigments and lipids have been examined during a 5-year period in two commercial solar salterns located in the United States and in Israel. There were significant differences in the complexity of the lipid and pigment patterns within the California saltern system, and these differences were not consistent over the sampling period despite examination of ponds with the same salinity. The solar saltern system in Eilat, Israel, showed greater consistency during this sampling period and compared directly with previous studies. The complexity of the saltern in Newark, California, could be explained on the basis of the prevailing weather conditions (cooler and more rainfall) and the nutrient-enriched source water. The Eilat saltern, however, has an oligotrophic water source and has a considerably warmer and drier climate. This difference resulted in more diverse and more complex pigment and lipid patterns and presumably microbial populations in the Newark, California, plant than in the saltern in Eilat, Israel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007920070011
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  • 9
    Electronic Resource
    Electronic Resource
    Testing the new welfare: Lessons from a survey of small business (2000)
    Springer
    Policy sciences 33 (2000), S. 55-71 
    Details
    ISSN: 1573-0891
    Source: Springer Online Journal Archives 1860-2000
    Topics: Political Science , Economics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004642026197
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  • 10
    Electronic Resource
    Electronic Resource
    Solving the Unit Commitment Problem by a Unit Decommitment Method (2000)
    Springer
    Journal of optimization theory and applications 105 (2000), S. 707-730 
    Details
    ISSN: 1573-2878
    Keywords: power system scheduling ; unit commitment ; unit decommitment ; mixed-integer programming ; Lagrangian relaxation ; heuristic procedures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we present a unified decommitment method to solve the unit commitment problem. This method starts with a solution having all available units online at all hours in the planning horizon and determines an optimal strategy for decommitting units one at a time. We show that the proposed method may be viewed as an approximate implementation of the Lagrangian relaxation approach and that the number of iterations is bounded by the number of units. Numerical tests suggest that the proposed method is a reliable, efficient, and robust approach for solving the unit commitment problem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004653526131
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