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.
A commercial variety of pole tomato (Lycopersicon esculentum Mill. H-11) was exposed to 20 and 35 parts per hundred million (pphm) ozone for 2.5 hours, 3 days each week over a period of weeks. Extensive foliar injury, defoliation, and highly significant reductions in plant biomass occurred at both exposure levels. However, fruit yield was significantly reduced only at the higher 35 pphm ozone concentration. This reduction was due to a decrease in the number of fruit and not to a decrease in fruit weight. Fruit yield in the 20 pphm treatment was equal to that of the control despite a 27% reduction in total dry weight of plants. These results indicate the presence of a threshold for the effect of ozone on yield.Additional Index Words: foliar injury, fruit, threshold.
Air pollution injury of the potato plant (Solanum tuberosum L.) has been documented previously, but potato yield losses have not been estimated in replicated experiments having controlled exposures to ozone (O3) and sulfur dioxide (SO2) A controlled‐environment study involving the speckle‐leaf‐sensitive cultivar ‘Centennial Russet’ was conducted to examine the effects of chronic exposure to O3 and SO2 on plant growth and tuber yield and quality.Ozone, at the highest seasonal dose (44.2 ppm‐h), reduced leaf dry weight 48%, root dry weight 58%, tuber number 38%, and total tuber yield 45%. Lower exposures affected these parameters in linear proportion to the O3 dose. Mean stem (minus leaves) dry weight, tuber dry weight, tuber dry matter percentage, partitioning of dry matter to tubers, and tuber sugar concentrations were not affected. Tuber N concentration increased linearly by up to 21% as the O3 dose increased. Plants grown outside of chambers in ambient air showed effects consistent with results obtained within the chambers. The plants grown outside received a total seasonal O3 dose of 50.4 ppm‐h and produced 58% less tuber yield than filtered air control plants.Plant responses to SO2 exposure were much less pronounced than their responses to exposure to O3. However, leaf symptom development in O3‐treated plants was markedly intensified by the presence of SO2. Small reductions in tuber yield and mean tuber size, but not in tuber number, were observed in SO2‐treated plants. Tuber N concentration increased slightly in SO2‐treated plants.A significant O3 × SO2 interaction was observed in the case of tuber N concentration only; SO2 accentuated the O3‐induced increase in N content.
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