© 1994 Heron Publishing—Victoria, Canada
Changes in gas exchange characteristics during the life span of giant sequoia: implications for response to current and future
concentrations of atmospheric ozone
N. E. Grulke (1, 2) and P. R. Miller (1)
1. USDA Forest Service, Pacific Southwest Forest Research Station, 4955 Canyon Crest Drive, Riverside, CA 92507, USA / 2. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA / Received August 16, 1993
Summary
Native stands of giant sequoia (Sequoiadendron giganteum Bucholz) are being exposed to relatively high concentrations of atmospheric ozone produced in urban and agricultural areas
upwind. The expected change in environmental conditions over the next 100 years is likely to be unprecedented in the life
span (about 2,500 years) of giant sequoia. We determined changes in physiological responses of three age classes of giant
sequoia (current-year, 12-, and 125-year-old) to differing concentrations of ozone, and assessed age-related differences in
sensitivity to pollutants by examining physiological changes (gas exchange, water use efficiency) across the life span of
giant sequoia (current-year, 2-, 5-, 20-, 125-, and > 2,000-year-old trees). The CO2 exchange rate (CER) was greater in current-year (12.1 µmol CO2 m–2 s–1) and 2-year-old seedlings (4.8 µmol CO2 m–2 s–1) than in all older trees (3.0 µmol CO2 m–2 s–1, averaged across the four older age classes). Dark respiration was highest for current-year seedlings (–6.5 ± 0.7 µmol CO2 m–2 s–1) and was increased twofold in symptomatic individuals exposed to elevated ozone concentrations. Stomatal conductance (gs) was greater in current-year (355 mmol H2O m–2 s–1) and 2-year-old seedlings (200 mmol H2O m–2 s–1) than in all older trees (50 mmol H2O m–2 s–1), indicating that the ozone concentration in substomatal cavities is higher in young seedlings than in trees. Significant
changes in water use efficiency, as indicated by Ci/Ca, occurred in trees between ages 5 and 20 years. We conclude that giant sequoias seedlings are sensitive to atmospheric ozone
until they are about 5 years old. Low conductance, high water use efficiency, and compact mesophyll all contribute to a natural
ozone tolerance, or defense, or both, in foliage of older trees.
Keywords:
carbon dioxide exchange, mesophyll, respiration, Sequoiadendron giganteum, stomatal conductance, water use efficiency.
