Influence of Ozone Stress on Soybean Response to Carbon Dioxide Enrichment: III. Yield and Seed Quality
1998
Ozone in the troposphere can cause plant stress, whereas elevated CO₂ generally causes positive responses. Little is known of how these gases interact to affect plant response. Interactive effects on yield and seed quality of soybean [Glycine max (L.) Merr.] grown in 14-L pots were measured in open-top field chambers. Essex was tested in 1993, and Essex, Holladay, and NK 6955 were tested in 1994. Plants were exposed from emergence to maturity to four CO₂ levels (ambient and 1.3,1.6, and 2.0 times ambient) and three O₃ levels (0.4, 0.9, and 1.5 times ambient) in 12 combinations. Increasing O₃ suppressed growth and yield, whereas CO₂ enrichment stimulated growth and yield. Carbon dioxide-induced stimulation was greater for plants stressed by O₃ than for non stressed plants. For example, CO₂ at 2.0 times ambient increased 2-yr mean seed yield of Essex by 16, 24, and 81% at O₂ levels of 0.4, 0.9, and 1.5 times ambient, respectively. Effects of O₃ and CO₂ on seed oil content were variable with numerous cultivar differences. Seed protein content was never affected. Elevated O₃ suppressed oleic acid content in seeds, whereas CO₂ increased it; the nature of the O₃ × CO₂ interaction for oleic acid was similar to that observed for most yield measures. Carbon dioxide-induced stimulation of plants stressed by O₃ was apparently caused partly by amelioration of O₃ stress. Interactions between O₃ and CO₂ must be considered for proper interpretation of cause-effect relationships in CO₂, enrichment studies. Cooperative investigations of the USDA-ARS Air Quality Research Unit and the North Carolina State University. Funded in part by the North Carolina Agricultural Research Service.
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