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ANALYSIS OF THE RELATIONSHIPS AMONG OZONE UPTAKE, CONDUCTANCE, AND PHOTOSYNTHESIS IN NEEDLES OF PINUS PONDEROSA
Citation:
Weber, J., W. Hogsett, AND C. Clark. ANALYSIS OF THE RELATIONSHIPS AMONG OZONE UPTAKE, CONDUCTANCE, AND PHOTOSYNTHESIS IN NEEDLES OF PINUS PONDEROSA. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-93/441 (NTIS PB94113719).
Description:
Determination of the relationships of conductance and photosynthesis to ozone uptake is important for the prediction of the long-term response of trees to ozone exposure. e studied the effects of O3 uptake on conductance (gwv) and photosynthesis (A) in needles of ponderosa pine (Pinus ponderosa Laws.) seedlings exposed for 70 days to one of three O3 regimes -- Low-O3, High-O3, and Low/High-O3. eedlings exposed to charcoal-filtered air served as controls. otal O3 exposures, expressed as ppm-h (the sum of the average hourly concentration to ppm over the exposure period), were 77, 135, 105, and 4 for the Low-O3, High-O3, Low/High-O3, and control treatments, respectively. onductance declined to about 60% of the value in control seedlings by Day 6 in seedlings in the High-O3 treatment and by Day 37 in seedlings in the Low/High-O3 treatment, but did not decline at all in seedlings in the Low-03 treatment. Our data indicate that O3-induced stomatal closure was a result of reduced A and that decreased gwv reduced O3 uptake to a rate that needles of ponderosa pine could tolerate without exhibiting further reductions in gas exchange capacity.