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Freezing of Conifer Xylem and the Cohesion‐Tension Theory

1969; Wiley; Volume: 22; Issue: 2 Linguagem: Inglês

10.1111/j.1399-3054.1969.tb07394.x

1399-3054

Edward Sucoff,

Biocrusts and Microbial Ecology

Abstract The research explored the apparent contradiction between the cohesion‐tension theory and the lack of blockage following freezing in conifers. Five to ten cm lengths of the main stem of actively transpiring Thuja occidentalis, Picea glauca and Pinus sylvestris were frozen. On thaw, there was no evidence of blockage in the formerly frozen xylem. Microscopic examination of frozen wood and hydrodynamic considerations showed that air was present in the xylem water and that bubbles were probably present upon freezing. On freezing about 9 per cent of the water irreversibly migrated into the unfrozen plant parts. Lack of blockage in the presence of air bubbles was reconciled to the cohesion‐tension theory by a model in which only the largest bubble in a number of interconnected cells expands. As this bubble expands tension is released allowing all bubbles in adjoining tracheids to redissolve. Potential rate of resolution of unexpanded bubbles following release of tension was calculated to be less than 0. 1 second.