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Gases can escape the xylem during freezing

Winter embolism is a major stress for trees of cold climates. While freezing occurs, gas bubbles are formed in the water-conducting structures (conduits), as gases are not soluble in ice. During thawing, the bubbles may expand and fill the conduits with air, causing decreased water conductance.

Lintunen et al. hypothesized that some of the gas might leak out from the conduits, decreasing the probability of embolism. They conducted CO2 efflux measurements for conifers in laboratory experiments and in field conditions and found substantial freezing-related CO2 bursts from the stem. It seems that all gases dissolved in the xylem sap are not trapped within the ice during freezing, as previously assumed. This study adds a new dimension to the understanding of winter embolism formation.

The article:
A. Lintunen, L. Lindfors, P. Kolari, E. Juurola, E. Nikinmaa & T. Hölttä:
Bursts of CO2 released during freezing offer a new perspective on avoidance of winter embolism in trees
Annals of Botany 2014
doi: 10.1093/aob/mcu190

More information:
Postdoctoral researcher, D.Sc. (Agriculture and Forestry) Anna Lintunen (name.surname[at]helsinki.fi).

Text: Anna Lintunen