Project at a Glance

Title: Effects of air pollutants on photosynthesis, vegetative growth, and development

Principal Investigator / Author(s): Williams, Larry E

Contractor: UC Davis

Contract Number: A6-124-33

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Ecosystem Impacts


Mature Thompson Seedless grapevines were exposed to charcoal filtered or ambient ozone concentrations in open-top chambers near Fresno, California, during the 1987 growing season. In addition, individual leaves were exposed to ozone concetrations of 200, 400 or 600 ppb for five to ten hours. No visual ozone damage was found on leaves exposed to any of the treatments. Chronic exposure to ambient ozone concentrations within the open-top chambers reduced net CO2 assimilation rate between 5 and 14% at various times throughout the season when comparing the ambient treatment to the charcoal filtered treatment. Treatment means averaged over the four dates on which measurements were made indicated that leaf photosynthesis was reduced approximately 9% in the ambient chambers when compared to the filtered grown vines. The initial slope of a photosynthesis / intercellular CO2 concentration response curve (termed the carboxylation efficiency) also was less for the ambient treatment when compared to the filtered treatment. Exposure of leaves to 200 ppb ozone for five hours had no effect on photosynthesis. However, photosynthesis was reduced approximately 50 and 80% after five hours for leaves exposed to 400 and 600 ppb ozone, respectively, when compared to the controls.

Generally, there were no significant decreases in vine growth parameters, bud fruitfulness or yield when comparing vines grown in the open - top chambers exposed to either filtered or ambient air. The lack of significant differences in the growth and yield of these vines probably was due to chamber effects. The amount of fruit produced by the chamber grown vines only was 50% of that produced on vines grown outside the chambers. Vines within the chambers apparently had become alternate bearing, as yields in 1987 were similar to those in 1985. Yields in 1984 and 1986 of chamber grown vines were almost double those harvested in 1985 and 1987.

Net CO2 assimilation rates of four out of six potted grape cultivars exposed to 1.5 times the ambient ozone concentration were approximately 25% less than those grown in the charcoal filtered chambers when measured late in the growing season. The net CO2 assimilation rate of a fifth cultivar, French Colombard, was reduced greater than 50% when making a similar comparison. The cultivar Barbera had greater rates of photosynthesis at the higher ozone concentration.

The data indicate that ambient ozone concentration in teh San Joaquin Valley of California are great enough to decrease grapevine leaf net CO2 assimilation. However, it is uncertain whether the reduction in photosynthesis is directly responsible for the reductions in yield that previously have been measured on vines in this area. The data also indicate that the reductions in photosynthesis due to both ambient and acute concentrations of ozone are a result of reduction in the mesophyll's capacity to fix CO2. Lastly, cultivar may determine, in part, a vine's sensitivity to ozone.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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