Freezing-related CO₂ bursts reduce winter embolism

Gases are not soluble in ice, so winter freezing of sap can lead to bubble formation in conducting vessels and hence to winter embolism when thawing occurs. Lintunen et al. measure CO₂ efflux from stems of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) saplings and find that substantial freezing-related bursts of CO₂ are released under both laboratory and field conditions. The results indicate that not all gases dissolved in the xylem sap are trapped within the ice in the stem during freezing, as has previously been assumed, and that release of gases can be important in avoiding winter embolism.