EFFECTS OF ELEVATED CO2 AND TEMPERATURE ON COLD-HARDINESS AND SPRING BUD BURST AND GROWTH IN DOUGLAS-FIR (PSEUDOTSUGA-MENZIESII)

We examined effects of elevated CO2 and temperature on cold hardiness and bud burst of Douglas-fir (Pseudotsuga menziesii (Mirb.) France) se edlings. Two-year-old seedlings were grown for 2.5 years in semi-close d, sunlit chambers at either ambient or elevated (ambient + approximat e to 4 degrees C) air temperature in the presence of an ambient or ele vated (ambient + approximate to 200 ppm) CO2 concentration. The elevat ed temperature treatment delayed needle cold hardening in the autumn a nd slowed dehardening in the spring. At maximum hardiness, trees in th e elevated temperature treatment were less hardy by about 7 degrees C than trees in the ambient temperature treatment. In general, trees exp osed to elevated CO2 were slightly less hardy during hardening and deh ardening than trees exposed to ambient CO2. For trees in the elevated temperature treatments, date to 30% burst of branch terminal buds was advanced by about 6 and 15 days in the presence of elevated CO2 and am bient CO2, respectively. After bud burst started, however, the rate of increase in % bud burst was slower in the elevated temperature treatm ents than in the ambient temperature treatments. Time of bud burst was more synchronous and bud burst was completed within a shorter period in trees at ambient temperature (with and without elevated CO2) than i n trees at elevated temperature. Exposure to elevated temperature redu ced final % bud burst of both leader and branch terminal buds and redu ced growth of the leader shoot. We conclude that climatic warming will influence the physiological processes of dormancy and cold hardiness development in Douglas-fir growing in the relatively mild temperate re gion of western Oregon, reducing bud burst and shoot growth.