%0 Journal Article %1 Lemoineetal_99 %A Lemoine, D. %A Granier, A. %A Cochard, H. %D 1999 %J Trees %K bibtex-import, citeulikeExport diameter, freezebolism, snowgumpapermaybe %P 206--210 %T Mechanism of freeze-induced embolism in Fagus sylvatica L. %U http://www.springerlink.com/index/JH84BCBN1JM6JHKA.pdf %V 13 %X Excised branches were subjected to successive freeze-thaw cycles. Exotherms detected. Loss hydraulic conductivity detected embolism after each freeze. Distal shoots froze 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. The higher vulnerability of shoot apices may protect the rest of the branch from winter damage. 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.

@article{Lemoineetal_99, abstract = {{Excised branches were subjected to successive freeze-thaw cycles. Exotherms detected. Loss hydraulic conductivity detected embolism after each freeze. Distal shoots froze 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. The higher vulnerability of shoot apices may protect the rest of the branch from winter damage. 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.}}, added-at = {2019-03-31T01:14:40.000+0100}, author = {Lemoine, D. and Granier, A. and Cochard, H.}, biburl = {https://www.bibsonomy.org/bibtex/2e5d31eb7147e84bde8c0c04ae9d2a786/dianella}, citeulike-article-id = {1523808}, citeulike-linkout-0 = {http://www.springerlink.com/index/JH84BCBN1JM6JHKA.pdf}, comment = {(private-note)The degree of embolism may influence plant success in colder environments (Tyree et al. 1994, Langan et al. 1997) Current thinking (which I disagree with): When sap freezes, air comes out of solution, becomes bubbles, trapped in the ice. The risk of embolism formation will depend on the stability of these bubbles when released into the liquid phase upon thawing. This stability is mainly determined by the balance between the pressures at the air-water meniscus of the bubble. Correlation between conduit VOLUME and vulnerability" (cochard and Tyree 1990, wang et al 1992, sperry and Sullivan, 1992, Lo Gullo and Salleo 1993). The apical vulnerability seen in this experiment (where the vessels are smaller in volume) contradicts this theory. Cut branches are totally enclosed in a chamber. Reduced from 20 to -10?C over 4 hours (-7.5?Cper hour) (max change in field was -6?C per hour) Thawed under tension (vacuum pump to estimate pressures in field) by removing from freezer, left to warm on bench. Some elegant controls. Water flow through a branch segment during freeze-thaw cycles by sticking the stem in an insulated chamber with the ends protruding out, and water-filled tubes attached to them. Ends feed onto 2 balances, one 90cm above branch, one 130cm below branch/attached to a vacuum pump Pressures used. Freezing caused water expulsion, thawing caused water uptake! Water exudation was probably the main cause of embolism in the apical shoots. When water movement was freely allowed on thawing, little embolism was observed. The exudation of water on freezing probably caused higher tensions on thawing. Alternative means of embolism: Ice sublimation (Sperry et al 1998) Mainly seen in more exposed twigs with higher SA:Vol. Terminal twigs good candidates. But that was in Acer, and Acer is UNUSUAL because it takes up water while freezing (tyree 1983!!!)(So this is UNUSUAL?) Embolism in the younger parts of the branch might protect the older parts from damage *But surely the younger parts are the most useful!* Under field conditions, the observed vulnerability of the terminal twigs would be even more pronounced, because they freeze first, and are the first to receive direct sunlight. *I have my own conclusion: the tips freeze first to protect themselves from supercooling. Embolism is easily fixed.}, interhash = {8c180968386e4e832a7e82d2279de93d}, intrahash = {e5d31eb7147e84bde8c0c04ae9d2a786}, journal = {Trees}, keywords = {bibtex-import, citeulikeExport diameter, freezebolism, snowgumpapermaybe}, pages = {206--210}, posted-at = {2007-07-31 06:37:44}, priority = {2}, timestamp = {2019-03-31T01:16:26.000+0100}, title = {{Mechanism of freeze-induced embolism in Fagus sylvatica L.}}, url = {http://www.springerlink.com/index/JH84BCBN1JM6JHKA.pdf}, volume = 13, year = 1999 }