The Effects of Ozone on the Growth, Yield, and Partitioning of Dry Matter in Cotton

Cotton (Gossypium hirsutum L.) Alcala SJ‐2 was grown in an activated carbon‐filtered greenhouse and exposed to biweekly 6‐hour ozone fumigations at a concentration of 490 µg m−3. Two ozone treatments were used, differing in age at initial exposure and total ozone dose. Sacrificial harvests were taken from all treatments at 14‐day intervals to monitor plant response and to provide the basis for growth analysis techniques. Ozone reduced the vegetative growth and boll production in both ozone treatments. The dry weights of all partitioned plant parts were reduced with the largest reductions occurring in roots and bolls. Fumigated plants initially produced fewer leaves with significantly less leaf area. A period of stimulated leaf and branch production followed the initial growth depression. Boll production was depressed 48% in both ozone treatments. Mean relative growth rates of partitioned plant parts were extremely good predictors of absolute responses. Mean net assimilation rates of ozone‐stressed plants were reduced throughout growth. The ozone‐treated plants were characterized by larger mean leaf area ratios, which accounted for elevated plant mean relative growth rates at 64 days of age.