The influence of ozone exposure dynamics on the growth and yield of kidney bean

Abstract

A field experiment was conducted in open-top chambers to assess the importance of peak exposure concentration and exposure frequency on the responses of kidney bean plants to O 3. There were five treatments in the study: charcoal-filtered air, constant exposure to 0·05 ppm O 3 (131 μg m −3) daily. fluctuating exposure to 0·08 ppm O 3 on three alternate days, cluster exposure to 0·08 ppm O 3 on three consecutive days, and peak exposure to 0·12 ppm O 3 on two consecutive days. Exposures lasted 4 h and produced an average weekly exposure-period concentration of approximately 0·05 ppm in the O 3− addition treatments and 0·025 ppm in the charcoal-filtered treatment. Exposures began on June 23 and terminated on September 8. Plants were harvested weekly and assessed for the number, area, and dry mass of leaves; dry mass of stems; dry mass of roots; the number of pods; and the incidence of foliar O 3 injury. Yield was assessed at the end of the study. There were no consistent differences between the plants receiving charcoal-filtered air and those receiving O 3 exposure. Significant differences were detected among the treatments for several of the growth variables assessed at the interim harvests, but in the final two harvests these differences had mostly disappeared. There were no significant effects of the O 3-addition treatments on yield when compared to the plants receiving charcoal-filtered air. This indicates that there were no cumulative impacts on plants exposed to 0·12 ppm O 3 for 4 h on two consecutive days followed by filtered air compared to plants receiving charcoal-filtered air. The seasonal 7-h average concentrations of O 3 in the peak and filtered air treatments were approximately 0·040 and 0·025 ppm, respectively.