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  • European Alps  (1)
  • Picea  (1)
  • 1995-1999  (1)
  • 1985-1989  (1)
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  • 1995-1999  (1)
  • 1985-1989  (1)
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  • 1
    ISSN: 1432-1939
    Keywords: Photosynthesis ; Specific leaf weight ; Carbon balance ; Larix ; Picea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Canopy photosynthesis is difficult to measure directly or to predict with complex models demanding knowledge of seasonal variation in environmental and physiological properties of the canopy. Trees in particular offer a challenge with their large, aerodynamically rough and seasonally-changing canopy properties. In this paper we assess the possibility of using specific leaf weight to predict seasonal and annual net photosynthetic rate in deciduous (Larix sp.) and evergreen (Picea abies) conifers. Annual photosynthetic rate and specific leaf weight of different positions of the crown in both species were highly correlated (r 2=0.930). Annual carbon uptake by different segments in a mature P. abies crown was closely related to leaf biomass. The relationship was improved by adjusting the leaf biomass of each segment in regard to its specific leaf weight relative to the maximum found in the canopy. The adjustment accounted for associated differences in photosynthetic activity. This combined structural index (leaf biomassxrelative specific leaf weight) could, when calibrated, predict the total annual carbon uptake by different parts of the crown. If direct measurements of photosynthesis are not available, the combined structural index may still serve as a comparative estimator of annual carbon uptake.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Water, air & soil pollution 116 (1999), S. 199-226 
    ISSN: 1573-2932
    Keywords: Tropospheric ozone ; Forests ; Ecological risk analysis ; Critical levels ; Free-air fumigation ; Visible injury ; European Alps
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Tropospheric ozone (O3) may adversely affect tree growth, with critical levels for O3 being exceeded in many parts of Europe. However, unequivocal evidence for O3-induced foliar injury on woody species under field conditions has only been found in a few places. Visible O3 injury appears to occur mainly in the Mediterranean Basin, which is also the area where the least amount of information is available on O3 exposure as well as the sensitivity of individual species. Overall, the quantitative risk assessment of O3 impacts on mature trees and forests is vague at the European scale, as most knowledge is derived from controlled O3 fumigations of young trees, grown in isolation in exposure chambers. Research suggests that risks exist, but these need to be validated for stand conditions. O3-induced changes in resource allocation rather than productivity appear to be crucial as they affect competitiveness and predisposition to parasite attack and may eventually lead to the loss of genetic diversity. ‘Free-air’ O3 fumigations in forest canopies may reveal processes that are susceptible to O3 stress under field conditions and provide a scientific basis towards quantitative risk assessment and realistic definitions of critical levels for O3 in forest ecosystems.
    Type of Medium: Electronic Resource
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