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  • 1
    Electronic Resource
    Electronic Resource
    Continuous measurements of water tensions in the xylem of trees based on the elastic properties of wood (1997)
    Springer
    Planta 202 (1997), S. 455-461 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Cohesion theory ; Linear variable displa cement transducer ; Modulus of elasticity ; Pinus ; Water potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. According to the cohesion theory for the ascent of water in vascular plants, significant tensions should develop in the water columns of transpiring trees. These tensions cause small but detectable changes in the diameter of the xylem as a consequence of adhesive forces between water molecules and the inner xylem walls. The diurnal time course of tension in the water columns in the xylem of the trunk of mature Scots pine (Pinus sylvestris L.) was measured during the summer of 1995 by means of a displacement transducer mounted on a rigid steel frame. The apparent elastic modulus of Scots pine wood in the radial direction (E  ′ r ) was determined in the laboratory and then used to estimate tensions from the measured displacement. Laboratory measurements on logs indicated that only the sapwood contributed to dimensional changes of the xylem. Corrections for thermal expansion of the system were included. Water tensions fell by 0.19 MPa over the course of the day, when needle water potentials fell by 0.50 MPa. Such data are consistent with the cohesion theory, and with the view that the hydraulic resistances to flow in above- and below-ground plant parts are of similar magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050149
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Climate and the meristem temperatures of plant communities near the tree-line (1989)
    Springer
    Oecologia 79 (1989), S. 198-204 
    Details
    ISSN: 1432-1939
    Keywords: Tree-line ; Montane microclimates ; Pinus ; Krummholz ; Energy balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Temperatures of terminal meristems of forest, krummholz and dwarf shrub vegetation were measured at altitudes of 450, 600, 650 and 850 m in the Cairngorm Mountains of Scotland. Simultaneously, the air temperature above the vegetation was recorded, so that it was possible to calculate the difference between meristem and air temperature, sometimes called the excess temperature. This temperature increased linearly with the net radiation absorbed at each station, and the slope was dependent on wind speed and the height of the vegetation. In the extreme cases the slopes were practically zero for forest and 0.028° C W-1 m2 for dwarf shrubs. The latter implies a temperature excess of about 15° C in bright sunshine and low wind speeds. A model is developed to calculate the excess temperature from a knowledge of vegetational height and climatological variables.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388479
    Location Call Number Limitation Availability
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    Paper (German National Licenses)
    Fulltext
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