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Free Content Switching the light off: A break in photosynthesis and sap flow of forest trees under total solar eclipse

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Abstract:

In mature trees of Picea abies, Fagus sylvatica and Quercus robur, photosynthesis and transpiration were assessed in response to the total solar eclipse that occurred in Central Europe during the late morning hours of August 11, 1999, a day with changing cloudiness. Measurements were conducted at three forest sites located in the totality zone and the 99% area of the eclipse within a radius of about 100 km around the city of Munich (southern Germany). The eclipse lasting 164 minutes lowered the photosynthetic photon flux density (PPFD) to about 1 μmol m-2 s-1 during the 2-minute totality period, when the sky was clear. During totality, photosynthesis was reduced to an extent that allowed CO2 release to dominate the gas exchange of leaves. Effects on transpiration were less pronounced as the totality was apparently too short to induce distinct stomatal closure in response to low PPFD. Transpiration was strongly reduced, however, by increased air humidity and wet leaf surfaces during sporadic rain showers which preceded or succeeded the eclipse during the same day, whereas low PPFD through intermittent cloudiness during rain only moderately reduced photosynthesis. Although transpiration was lowered to a minor extent only by the eclipse, the latter affected the water transport through the whole tree, as reflected in a decline in the sap flow rate through the basal stem part with a time delay depending on the species. Nevertheless, trees responded in a synchronous way, regardless of the site, species or the percent degree of the eclipse.

An ausgewachsenen Waldbäumen der Arten Picea abies, Fagus sylvatica und Quercus robur wurde die Reaktion der Photosynthese und Transpiration auf die totale Sonnenfinsternis vom 11.8.1999 untersucht, einem Tag mit wechselnder Bewölkung. Die Messungen fanden an drei Waldstandorten im weiteren Münchner Umland statt, die innerhalb der Zone der Totalität oder in deren 99%-Bereich lagen. Während der Sonnenfinsternis, die insgesamt 164 Minuten dauerte, sank die Photonenflussdichte (PPFD) bei klarem Himmel bis auf 1 μmol m-2 s-1 in der zweiminütigen Totalitätsphase ab. Dabei brach die Photosynthese so stark ein, dass kurzfristig die respiratorische CO2-Freisetzung die photosynthetische CO2-Aufnahme überwog. Die Auswirkung auf die Transpiration war weniger ausgeprägt, da die Totalität offensichtlich von zu kurzer Dauer war, um eine Schließbewegung der Spaltöffnungen hervorzurufen. Die Transpiration wurde jedoch durch erhöhte Luftfeuchtigkeit und benetzte Blattoberflächen bei wiederholten Regenschauern am selben Tag vor und nach der Sonnenfinsternis stark reduziert, während die Photosynthese in diesen Fällen durch die - bewölkungsbedingt - geringere PPFD weniger stark beeinträchtigt war. Obwohl die Transpiration durch die Sonnenfinsternis nicht gravierend eingeschränkt war, senkte letztere den Wasserferntransport innerhalb der Bäume mit artspezifischer Verzögerung, wie Saftflussmessungen an den Stammbasen zeigten. Insgesamt reagierten die Bäume gleichartig, unabhängig von Standort, Baumart und Grad der Sonnenfinsternis.

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Document Type: Research Article

DOI: http://dx.doi.org/10.1127/0941-2948/2001/0010-0201

Publication date: May 1, 2001

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  • Meteorologische Zeitschrift (originally founded in 1866) is the joint periodical of the meteorological societies of Austria, Germany and Switzerland. It accepts high-quality peer-reviewed manuscripts on all aspects of observational, theoretical and computational research out of the entire field of meteorology, including climatology. Meteorologische Zeitschrift represents a natural forum for the meteorological community of Central Europe and worldwide.
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