The mechanism of stomatal closing in response to O_3 was indirectly investigated by using H_2O_2 which is the intermediate product of O_3 metabolites. Stomata in epidermal strips close in response to H_2O_2. The effect of H_2O_2 on stomatal closing was dependent on the concentration of H_2O_2. 10 ppm H_2O_2 showed a clear effect on stomatal closing and 1000 ppm H_2O_2 induced complete stomatal closing after the treatment of 3 hours. Stomatal closing by H_2O_2 in intact leaf was also observed by measuring the diffusion resistance with porometer. It was found that the stomatal closing by H_2O_2 was not mediated by Ca^2+, and that was a different result observed in stomatal closing by water stress. Reversely, Ca^2+, showed a great inhibition on stomatal closing. The leakage of K^+ in epidermal strips was doubled in response to H_2O_2 when it was campared to the control. 10 ppm H_2O_2 decreased photosynthetic activity. Fv/Fm representing the activity of Photosystem Ⅱ was reduced about 4 % in 10 ppm H_20_2 and 8 % in 100 ppm H_2O_2 in the treatment of 1.5 hour. However, stomatal closing by 10 ppm H_2O_2 was reduced about 56 %. Accordingly, it can be suggetsted that stomatal closing by H_2O_2 is related with the decrease of photosynthetic activity, but it was chiefly induced by the change of the membrane permeability.

At the close of the year 1990, tombs in south Korea will cover the area of 940 ㎢, which is 0.9% of the entire landspace. Annual increase of 200,000 tombs is encroaching on landspace by 10 ㎢. It is estimated that the decrease in the forest area caused by tombs results a decrease both in the production of O_2 by 912,000 tons and in the absorption of CO_2 by 1,254,800tons per year. As a result, there will be an increase in the amount of CO_2, which is one of the factors that cause the greenhouse effect.