Research Projects

Project at a Glance

Project Status: complete

Title: Investigation of the effects of acid deposition upon California crops

Principal Investigator / Author(s): Olszyk, David M.

Contractor: Statewide Air Pollution Research Center, UC Riverside

Contract Number: A5-087-32

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition, Agriculture, Ecosystem Impacts, Impacts


The Statewide Air Pollution Research Center has a continuing mission to investigate the effects of air pollutants on agricultural crops, native vegetation and forests, and to determine the amount of loss being caused by these pollutants. To further this mission we conducted the comprehensive study: "Investigation of the Effects of Acid Deposition upon California Crops." The study evaluated the relationship between doses of acidic fog at pH 1.8 to 5.5 and responses of important winter crops of the San Joaquin Valley (alfalfa, broccoli, carrot, onion, potato, and wheat), and fog at pH 1.7 to 7.2 on spring South Coast crops (alfalfa, celery, green pepper, strawberry, and tomato). The study also evaluated the interaction between acidic fog and ambient oxidants (primarily 03) on the South Coast crop species.

The spring fog and/or oxidant exposures were conducted in open-top field chambers maintained by the ARB at the University of California, Riverside, California. Ancillary exposures were conducted without chambers using air exclusion ducts in order to aid in interpreting the open-top field chamber results. The winter fog exposures were conducted under temporary covers, which were removed after each fog episode.

Plant response measurements emphasized physiological parameters which will provide data with respect to the metabolic basis for acidic fog and acidic fog/oxidant effects. The measures of leaf response included net photosynthesis, stomatal conductance, transpiration, element content, buffering capacity and chlorophyll concentration. Plant growth and yield measurements were made at the end of exposures.

For the spring study, fog at pH 1.68, 2.69 or 7.24 were applied twice weekly to potted plants grown in open-top field chamber or air exclusion plots for eleven weeks. Injury symptoms (i.e., necrosis) developed on leaves and fruits of all species exposed to pH 1.68 fog, but did not occur in plants exposed to pH 2.69 or 7.24 fog, or in plants that were not fogged. Season-Long exposure to pH 1.68 fog significantly reduced fruit yield in strawberry, tomato, and green pepper by 30 to 58 percent, and biomass yield in alfalfa by 11 percent relative to yields measured in crops exposed to pH 7.24 fog. In contrast, biomass yield in celery was not altered by pH 1.68 fog. Ambient levels of gaseous pollutants reduced yields in tomato, green pepper, alfalfa and celery. Overall, the combined effects of severe acidic fog (pH 1.68) and ambient gaseous pollutants were additive with respect to growth and yield responses in the five crops.

In general, the effects of the acidic fog treatments were less severe in the air exclusion than in the open-top chamber plots. The reduced effects were likely due to dilution of applied fog in ambient dew which occurred on leaves of plants grown in air exclusion systems and outside plots, but not in open-top chambers. Reduced replication in air exclusion chambers also likely played a role in lessened ability to detect statistically significant differences between treatments compared to open-top chambers.

For the winter study, fogs at pH 1.76, 2.23, 2.72, 3.22, and 5.48 were applied twice weekly to potted plants grown in ambient air for eleven weeks. Injury symptoms developed on leaves of all species exposed to pH 1.76 fog, and occasionally at pH 2.23 and 2.72. Season-long exposure to pH 2.23 fog affected leaf and shoot dry weight in broccoli, and pH 1.76 fog affected fresh and dry weights of all species, even though the reductions compared to the no fog or pH 5.5 condition were only statistically significant for broccoli. Whole season leaf transpiration, stomatal conductance, and net photosynthesis rates were reduced at pH 1.76 compared to pH 5.48 or no fog treatments for broccoli, but not potato.

Therefore, repeated application of only highly acidic fogs of pH 1.7-I.8 were generally phytotoxic. Species differed widely in their sensitivity to acidic fog in terms of yield and physiology, with green pepper and broccoli found to be the most sensitive in the spring and fall foggings, respectively. There was no evidence for any acidic fog-smog (ozone) interaction on these crops.


For questions regarding research reports, contact: Heather Choi at (916) 322-3893

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