Yield Responses of Field-Grown Crops to Acidic Fog and Ambient Ozone

The yield responses of five commercially important California crops (strawberry Fragaria × ananassa Duch., tomato Lycopersicon esculentum Mill., pepper Capsicum annuum L., alfalfa Medicago sativa L., celery Apium graveolens L.) to acidic fog singly, and in combination with ambient O₃ were examined under field conditions, utilizing open-top chambers and air exclusion systems. Simulated fog at pH 7.24, 2.69, or 1.68 was applied to plants twice weekly for 11 weeks. Only repeated applications of pH 1.68 fog were found to cause significant alterations in crop injury or yield responses compared to exposure to pH 7.24 fog. Necrotic lesions developed on leaves, flowers, and fruits of plants exposed to pH 1.68 fog, but not on plants exposed to pH 2.69 or 7.24 fog, or on unfogged plants. In plants grown in open-top chambers, pH 1.68 fog significantly reduced fruit yield in strawberry, tomato, and pepper by 30 to 58%, and biomass yield in alfalfa by 11% relative to yields measured in crops exposed to pH 7.24 fog. Moreover, significant yield reductions were observed in tomato, pepper, alfalfa, and celery exposed to ambient O₃ compared to crops grown in charcoal-filtered air. The combined effects of highly acidic fog (pH 1.68) and ambient O₃ were additive with respect to growth and yield responses in all five crops grown in open-top chambers. However, since fog at current ambient levels of acidity is typically 10 to 100 times less acidic, yield losses attributable to acidic fog alone, are not likely to occur. Alternatively, yield reductions may result as a consequence exposure to ambient O₃, but no interactive effect would be expected based on the results of the present study. Plant yield, growth, and injury responses to acidic fog and ambient O₃ in air exclusion system plots were not similar to those exhibited by plants grown in open-top chambers. The impacts of the applied stresses were less pronounced in plants grown in air exclusion systems, which may have been partly due to differences in environmental conditions between the exposure methodologies. Contribution of the Statewide Air Pollut. Res. Ctr., Univ. of California, Riverside, CA 92521.