Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài:The effects of summer exposure to ozone on the frost hardiness after the vegetation period of Norway and Sitka spruce seedlings. | 624s Ann. Sci. For. 1989 46 suppl. 624s-627s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA The effects of summer exposure to ozone on the frost hardiness after the vegetation period of Norway and Sitka spruce seedlings . Lucas Institute of Environmental and Biological Sciences Division of Biological Sciences University of Lancaster Lancaster LA1 4YQ . Introduction No single cause has been identified to explain the decline of coniferous trees in some high-elevation forests in Europe and parts of the USA but a consensus view among researchers is that the observed changes are associated with air pollutants. Air pollutants are however only one of a variety of environmental stresses which may affect the physiology of trees and which could predispose or incite damage. In those areas where forest declines are occurring daily mean ozone concentrations are often above 100 pg-nrr3. Exposure to elevated concentrations of ozone is known to damage cell membranes Heath 1980 . Since loss of membrane integrity is thought to be the major cause of frost injury Levitt 1980 there are good physiological reasons to believe that ozone could increase the sensitivity of plants to freezing injury. The objectives of the present study were to investigate whether long-term exposure to ozone during the summer af fected the frost hardening and dehardening of Norway spruce Picea abies L. Karst and Sitka spruce P. sitchensis Bong Carr such that their susceptibility to frost damage was increased. Materials and Methods Ozone fumigation and growth measurements At the beginning of May 1987 25 2 yr old seedlings of each species were assigned randomly to each of 4 large-scale fumigation chambers described previously by Lucas et al. 1987 . Fumigation of the seedlings began on 1 June 1987 and continued until 11 September 1987. In two of the chambers trees were exposed to ozone for 7 h each day 08 00-15 00 for 5 d per wk at an average hourly concentration of 140 w -3 the remaining .
