Effect of Ozone and Simulated Acid Rain on Growth, Nitrogen Fixation and Peroxidase Activity in Faba Bean ( Vicia faba L.) Plant

摘要

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.