Mechanism of freeze-induced embolism in Fagus sylvatica L. |
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Authors: | Damien Lemoine André Granier H Cochard |
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Institution: | (1) Unité d’Ecophysiologie Forestière, INRA Nancy, F-54280 Champenoux, France, FR |
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Abstract: | The mechanism of freeze stress-induced embolism in Fagus sylvatica L. branches was analyzed under controlled conditions. Excised branches were exposed to successive freeze-thaw cycles in temperature
controlled chambers. Thermocouples were placed on the bark to detect sap freezing exotherms. The degree of xylem embolism
was estimated after each cycle by the loss of hydraulic conductivity. After one freeze-thaw cycle the degree of embolism was
found to decrease with xylem specific hydraulic conductivity, small apical shoots being more susceptible to embolism. Exotherms
revealed that distal shoots were freezing first and exuded sap as a result of water expansion. The lower water content in
apical shoots upon freezing probably induced higher sap tensions which promoted air bubble expansion and vessel cavitation
preferentially near the apices. When the decrease in water content was experimentally prevented, embolism developed to a lesser
extent. The higher vulnerability of shoot apices may protect the rest of the branch from winter damage.
Received: 29 May 1998 / Accepted: 15 August 1998 |
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Keywords: | Beech (Fagus sylvatica L ) Cavitation Conductivity Xylem embolism Freeze-thaw |
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