© 1996 Heron Publishing—Victoria, Canada
Response of giant sequoia canopy foliage to elevated concentrations of atmospheric ozone
N. E. Grulke, P. R. Miller and D. Scioli
USDA Forest Service, Pacific Southwest Research Station, 4955 Canyon Crest Drive, Riverside, CA 92507, USA / Received May 11, 1995
Summary
We examined the physiological response of foliage in the upper third of the canopy of 125-year-old giant sequoia (Sequoiadendron giganteum Buchholz.) trees to a 61-day exposure to 0.25×, 1×, 2× or 3× ambient ozone concentration. Four branch exposure chambers,
one per ozone treatment, were installed on 1-m long secondary branches of each tree at a height of 34 m.
No visible symptoms of foliar ozone damage were apparent throughout the 61-day exposure period and none of the ozone treatments
affected branch growth. Despite the similarity in ozone concentrations in the branch chambers within a treatment, the trees
exhibited different physiological responses to increasing ozone uptake. Differences in diurnal and seasonal patterns of gs among the trees led to a 2-fold greater ozone uptake in tree No. 2 compared with trees Nos. 1 and 3. Tree No. 3 had significantly
higher CER and gs at 0.25× ambient ozone than trees Nos. 1 and 2, and gs and CER of tree No. 3 declined with increasing ozone uptake. The y-intercept of the regression for dark respiration versus ozone uptake was significantly lower for tree No. 2 than for trees
Nos. 1 and 3. In the 0.25× and 1× ozone treatments, the chlorophyll concentration of current-year foliage of trees Nos. 1
and 2 was significantly higher than that of current-year foliage of tree No. 3. Chlorophyll concentration of current-year
foliage on tree No. 1 did not decline with increasing ozone uptake. In all trees, total needle water potential decreased with
increasing ozone uptake, but turgor was constant. Although tree No. 2 had the greatest ozone uptake, gs was highest and foliar chlorophyll concentration was lowest in tree No. 3 in the 0.25× and 1× ambient atmospheric ozone treatments.
Keywords:
chlorophyll, ozone uptake, Sequoiadendron giganteum, stomatal conductance.
