Water Stress in Conifers During Winter

Abstract

In a northern continental climate the water supply to evergreen conifer needles is apparently cut off in the late autumn by the onset of frost. Transpiration still proceeds, however, even if the rate is reduced to a minimum. Consequently the needles must be exposed to a slowly increasing water stress. This results in a gradual reduction of the leaf water content during winter, and a corresponding increase hi the osmotic potential of the cell sap. If these changes should exceed a comparatively moderate range, the needles would die. Since most of them do survive after all, we are faced with the problem of how they may avoid excessive water loss.