Cold Tolerance and Photosystem Function in a Montane Red Spruce Population

Red spruce (Picea rubens Sarg.) growing in northern montane forests of eastern North America appears to be distinctive with respect to at least two aspects of winter physiology. First, red spruce attains only a modest level of midwinter cold tolerance compared to other north temperate conifers and appears barely capable of avoiding freezing injury at commonly occurring ambient winter temperatures (DeHayes, 1992). Second, red spruce is capable of net photosynthesis during winter in response to relatively brief exposure to mild temperatures (Schaberg et al., 1995). Despite considerable study, most of our understanding of red spruce cold tolerance and winter photosynthesis is derived from seedling studies in modified environments or examination of only a few mature trees in forests. As such, actual levels of attainment and the range among native trees are not well understood.