© 1998 Heron Publishing—Victoria, Canada
Effects of elevated CO2 and temperature on cold hardiness and spring bud burst and growth in Douglas-fir (Pseudotsuga menziesii)
Sunghee Guak (1), David M. Olsyzk (2), Leslie H. Fuchigami (1, 3) and David T. Tingey (2)
1. Department of Horticulture, Oregon State University, Corvallis, OR 97331, USA / 2. US EPA, National Health and Environmental Effects Research Laboratory, Western Ecology Division, Corvallis, OR 97333, USA / 3. Author to whom correspondence should be addressed (fuchigal@bcc.orst.edu) / Received July 18, 1997
Summary
We examined effects of elevated CO2 and temperature on cold hardiness and bud burst of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Two-year-old seedlings were grown for 2.5 years in semi-closed, sunlit chambers at either ambient
or elevated (ambient + ~ 4 °C) air temperature in the presence of an ambient or elevated (ambient + ~ 200 ppm) CO2 concentration. The elevated temperature treatment delayed needle cold hardening in the autumn and slowed dehardening in the
spring. At maximum hardiness, trees in the elevated temperature treatment were less hardy by about 7 °C than trees in the
ambient temperature treatment. In general, trees exposed to elevated CO2 were slightly less hardy during hardening and dehardening 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 ambient CO2, respectively. After bud burst started, however, the rate of increase in % bud burst was slower in the elevated temperature
treatments 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 in trees at elevated temperature. Exposure to elevated temperature reduced final % bud burst of both leader and branch
terminal buds and reduced 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 region of western Oregon,
reducing bud burst and shoot growth.
Keywords:
chill days, chilling requirements, climate change, climatic warming, cold hardening, dehardening, elevated carbon dioxide,
thermal time, visible injury.
