DefinePK

Abstract

Faba beans (Vicia faba L. CV. Giza 400) were exposed to ozone (100 ppb) and simulated acid rain (SAR) at pH 3, separately and combined over 2-weaks period while grown in climate controlled growth chambers. Ozone fumigation (O3) exposure was for 5 h day -1, whereas acid rain exposure was for 2 h per week. The results showed that exposure to high O3 concentration (100 ppb) decreased the number and weight of root nodules, suppressed nitrogenase activity and strongly induced stomatal closure. Combination between high O3 concentration and acid rain generally caused more closure of the stomata than other treatments. Water content and leaf area were significantly reduced in high O3 treatment. Furthermore, high O3 concentration increased the shoot/root ratio by reducing root growth more than shoot growth In contrast, low O3 concentration had no effect on these parameters. Acid rain, on the other hand, decreased root nodulation and N2-fixation, but it ameliorated O3 induced injury. The reduced O3 injury induced in the presence of acid rain treatment was probably achieved by decreasing O3 uptake through stomatal closure. Furthermore, leaves treated with acid rain became greener than those of control and other treatments due to the increase in chlorophyll concentration. Peroxidase (POD) activity showed a positive response to ozone and acid rain treatments either combined or separately.