Effects of ozone on Pinus ponderosa seedlings: comparison of responses in the first and second growing seasons of exposure
1997
Takemoto, B.K. | Bytnerowicz, A. | Dawson, P.J. | Morrison, C.L. | Temple, P.J.
The present study was conducted in 1989 and 1990 at Shirley Meadow, southern Sierra Nevada, California. The objective was to evaluate the effects of ozone (O3) on the physiological and growth responses of Pinus ponderosa Dougl. ex P.& C. Laws.(ponderosa pine) seedlings. Seedlings were exposed to three levels of O3 in open-top chambers (charcoal-filtered air (CF), ambient O3 (1x O3), or twice-ambient O3 (2x O3)); 24-h average concentrations were approximately 20, approximately 60, and approximately 120 ppb, respectively. In the first growing season, current-year needles in plants exposed to 2x O3 exhibited greater needle injury, and periodic decreases in chlorophyll fluorescence and net photosynthesis, but no significant effects on plant growth. In the second growing season, 1-year-old needles of seedlings exposed to 2x O3 exhibited significant reductions in physiological and biochemical responses, and plant growth was decreased relative to plants exposed to CF and 1x O3. These findings indicate the potential for insidious O3-caused growth declines in ponderosa pine seedlings after successive growing seasons.
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