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  • 1
    Digitale Medien
    Digitale Medien
    Poor stomatal control of water balance and the abscission of green needles from a declining stand of spruce trees [Picea abies (L.) Karst.] from the northern Alps (1995)
    Springer
    Trees 10 (1995), S. 63-73 
    Details
    ISSN: 1432-2285
    Schlagwort(e): Forest decline ; Osmotic potential ; Picea abies ; Stomatal control ; Water potential
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract On a site on the west slope of the Wank in the northern Alps changes in water potential, osmotic potential and transpiration rate were measured in spruce trees during the dry summer months of 1991. The pattern of decrease in water potential and osmotic potential on days of varying evaporative demand from trees of widely different decline conditions was used to describe the relative ability of the trees to withstand drought stress. Stress diagrams served as a tool for interpreting the state of health of each tree. The criterion is independent of the water situation of the tree and the other external conditions of the respective experiment. These diagrams clearly show that the foliage of spruces with high needle losses reaches the limit of endurance relatively early. For equal evaporative demand much lower turgor levels were observed in spruces with high needle loss compared to undamaged trees. Associated with the occurrence of low turgor values was the shedding of green needles. The abscission zone was shown in sections. The accumulation of highly fluorescent substances in the bundle sheath cells of the same material was described. Incomplete to non-existent stomatal control over water loss was attributed to modifications in the cell walls of the stomata which appear to alter the ability of the guard cells to sense changes in either atmospheric or cellular hydration. Our studies point to the following situation: air pollution directly affects stomatal control, the loss of stomatal control changes the drought avoidance abilities of the foliage and, as a consequence, low turgor levels occur and premature needle abscission is induced. As site water balance decreases, either due to a dry year or to poor moisture holding abilities of the soil, these conditions become apparent.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00192185
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  • 2
    Digitale Medien
    Digitale Medien
    Image analysis of the stomatal cell walls of Picea abies (L.) Karst. in pure and ozone-enriched air (1998)
    Springer
    Trees 12 (1998), S. 181-185 
    Details
    ISSN: 0931-1890
    Schlagwort(e): Key words Image analysis ; Ozone ; Picea abies ; Stomata ; UV-absorbance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  The method of image analysis was used to re-investigate previously described structural changes in spruce needles following their exposure to ozone. The changes observed in fumigation experiments were compared with the modifications observed at a site with a similar ozone load. Use was made in each case of needles for which the varying behavioural patterns were known from physiological experiments. In samples with reduced ability to regulate stomatal aperture, the cell walls of the stomatal apparatus showed a reduction in absorptive power at 280 nm. This was interpreted to be a result of delignification of the cell walls in question due to the direct impact of ozone on the surface of the needle.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009708
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  • 3
    Digitale Medien
    Digitale Medien
    Experiments on the water balance of individual attached twigs of Picea abies (L .) Karst. in pure and ozone-enriched air (1997)
    Springer
    Trees 11 (1997), S. 229-239 
    Details
    ISSN: 0931-1890
    Schlagwort(e): Key words Ozone ; Picea abies ; Stomatal control ; Water potential ; Xylem sap flow
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  Rates of transpiration and xylem sap flow were continuously measured in individual twigs in the upper crown of an 18-year-old spruce. Two gas exchange chambers were run simultaneously under identical conditions. One of two equivalent twigs was exposed to pure air whereas the other received the ozone-enriched air of the site. A third gas exchange chamber in mid-crown ran independently with normal outside air and was used for basic experiments. At certain times needles were sampled for water potential measurements. Chamber humidity was reduced step by step and the transpiration and xylem sap flow rates were permanently compared. It turned out that sap flow keeps up with transpiration without lagging as long as chamber humidity is high and the twigs outside the chamber are not subject to substantial evaporative demand. However, in warm summer weather and with high flow rates sap flow is no longer sufficient. As the balance quotient (uptake/release) of 0.8 was reached the stomata began to close and water balance improved. The flux quotient increased far above 1.0 without water potential of the needles, which had decreased before, increasing significantly. The balance quotient of the twig in ozone-enriched air fell to relatively low values and only increased again correspondingly slowly due to lagging stomatal closure. Despite increased water uptake after the light phase, the ozone-treated twig ran into a water deficit in the daily balance during the course of an uninterrupted drought period. Water deficit increased from day to day and only disappeared with the next rainfall. For providing insight into the ozone effect shown in this study it was thought necessary to discuss comprehensively the controversial views of the stomatal control mechanism. The results show that the stomata react to small scale changes in water status as expected for an effective negative feedback system. The less sensitive reaction of the stomata under the influence of ozone confirms earlier results. Increased severity and duration of the daily drought stress loads were attributed to a lag in adjustment due to poor stomatal control. The demonstrated function mechanism shows that the detrimental effect of ozone is dependent on weather conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009669
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  • 4
    Digitale Medien
    Digitale Medien
    Experiments on the water budget of densely and sparsely needled spruces [Picea abies (L.) Karst.] in a declining stand (1991)
    Springer
    Trees 5 (1991), S. 164-170 
    Details
    ISSN: 1432-2285
    Schlagwort(e): Forest decline ; Osmotic potential ; Picea abies ; Water content ; Water potential
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Summary The osmotic potentials of needles were compared from numerous trees that had been classified according to needle loss along an altitude profile. With the increasing degree of damage of the trees, the maximum and minimum values deviated more strongly above and below the common mean of all samples. The level of water content of the needles unequivocally reflected the vitality of the trees. Experiments covering a whole vegetation period were performed on a tree pair selected from a natural stand. They were designed to demonstrate differences in water balance between the “healthy” and “damaged” state of the trees. For the “damaged” tree, measurements of the water potentials of single needles showed a greater reduction of potential during the course of the day compared to the “healthy” tree. Recovery in the evenings was slower and often incomplete. The osmotic potentials of “damaged” and “healthy” shoots measured in individual needles also differed both predawn and especially after transpiration stress. Depending on weather and soil desiccation, the differences were more or less pronounced. In the “damaged” tree, the rises in potential after saturation of the twigs fell far short of the “healthy” tree. Reduction of water potential, osmotic potential and relative water content under comparable stress conditions suggest a reduced tolerance of drought by damaged trees. In the context of earlier experiments this result was ascribed to a lack of stomatal control, and long-term pollution effects were thus explained as a specific disturbance of hydroregulation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00204339
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  • 5
    Digitale Medien
    Digitale Medien
    Histological examination of spruce needles from a long-term gas exchange experiment in pure and polluted air in the field (1992)
    Springer
    Trees 6 (1992), S. 186-194 
    Details
    ISSN: 1432-2285
    Schlagwort(e): Air pollutants ; Bundle sheath ; Picea abies ; Stomata ; UV absorbance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Summary At the end of a 4-year period of gas exchange measurements in a natural stand in the Lower Bavarian Forest, needles of an adult spruce [Picea abies (L.) Karst.] were harvested from two chambers, one with pure air and the other with ambient air. The needles were examined as to their histological properties in the stomatal apparatus and in the bundle sheath. In needles from the polluted air UV absorbance at 280 nm was decreased in the walls of the stomatal apparatus. Simultaneously, the deposition of compounds with an absorption maximum at 310 nm increased within the encrusted plate-like thickenings of the subsidiary cells. The contents of the lumina of hypodermal cells and of the bundle sheath exhibited a greater degree of autofluorescence in ambient-air material than in pure-air leaf organs. Differences between needles exposed to pure and polluted air are gradual. The “damaged” condition is rare in pure air, common in polluted air. The needles from outside the chambers occupied an intermediate position between pure-air and ambient-air needles. This fact is traced to an unnaturally high pollutant load in the liquid phase of the needle surfaces within the ambient-air chamber because in order to compensate pollutant losses within the system, SO2 and O3 were added even during periods of irrigation. The reduction of absorption capacity at 280 nm in the walls of the stomatal apparatus is attributed to destruction of lignin due to the high reactivity of the pollutants in the liquid phase on the damp needle surface. The importance of delignification with regard to hydroregulation is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00224334
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