39 巻 (1975) 3 号 p. 29-33
In recent years many efforts have been made in the study of the resistance of trees and shrubs against sulphur dioxide. However, the seasonal changes of the resistance have never been given a proper attention, especially on report ever handled this change in the resistance of garden trees and shrubs over a period of one year. The purpose of this study is to investigate the seasonal changes in the resistance of garden trees and shrubs against sulphur dioxide, thus contributing to the problems of protection and maintenance of garden trees and shrubs in big cities, just when the role of plants in improving environmental conditions is beginning to draw wide attention.
The following garden plants (on tree and two shrubs) were used as the test samples;Kamakura-hiba Chamaecyparis obtusa Sieb. et Zucc. var. brevirainea Beiss.
Masaki Euonymus japonicus Thunb.
Satsuki-tsutsuji Rhododendron indicurn Sweet
The author planted these samples and exposed them to 3 ppm of SO2 for 3 hours under a given temperature in a growth cabinet for air-pollution experiments every other month for one year starting from May 1972, and observed the effects of the pollution and the state of growth after the disposure. Also, the author made a section where the plants were given an artificial shower (20mm'3mins.) after the exposure, and tried to observe effects of the watering in reducing the damages made by the pollution.
The general outlines of the results of the experiment are as follows:
1. Resistance of the test plants against sulphur dioxide is strongest during winter (January) and in the month right after winter (March). Resistance is also fairly strong in the month right before winter (November). On the contrary, it is the weakest in summer (July) and also weak in the month of September. In the month right before summer (May) damages appear in different degrees among different samples.
2. The rate of falling leaves which the author took as an indication of the damage showed the same trend seen in other features of damage.
3. Observation of growth of the plants after the disposure disclosed that no plant died: all of them recovered from the damage. As of March, all of Kamakura-hiba were growing normally, and Masakis and Satsuki-tsutsujis had returned to normal except those exposed in July and November. Those exposed in July were late in shooting out new leaves after the old ones had fallen, and those exposed in November shod their leaves toward the beginning of winter and consequently new leaves were not coming out yet.
4. No alleviating effects by watering were recog nized.
5. Generally, resistance against sulphur dioxide was strongest in Kamakura-hiba, next strongest in Masaki, and weakest in Satsuki-tsutsuji.