RESPONSE OF PHASEOLUS-VULGARIS L TO DIFFERING OZONE REGIMES HAVING IDENTICAL TOTAL EXPOSURE

Protocols were designed to test For differences in response of plants to ozone treatments having equal total exposure (concentration x time) but different exposure profiles. Kidney beans (Phaseolus vulgaris L., cv. California Dark Red) were exposed to ozone in controlled fumigation chambers within a greenhouse. Four different ozone exposure profiles were used, each having the same total cumulative exposure (SUMOO) and the same 7, 12 and 24 h seasonal means. The three exposure profiles which incorporated peak concentrations more severely impacted response parameters compared to a steady-state profile which did not exceed the National Ambient Air Quality Standard. Significant differences were found in percent necrotic leaf area, number of pods and top dry weight between exposure profiles. In additional analyses, the response parameters were regressed against seasonal cumulative ozone concentrations raised to powers of 0.33 and from 0.5 to 4 in steps of 0.5 in order to increase effective weighting of the higher concentrations. Total dry weight and leaf necrosis were best fit with the sum of the squared concentrations (n=2) while number of pods was best fit by the summed concentrations to the 3,5 power (n = 3.5). These analyses suggest the peak ozone concentrations are important in determining plant response.