Studies on the Damaged Symptoms of Fruit Crops Caused by Acid Rain and Their Sensitivity
Lu Junliang and Li Sanyu (Department of Horticulture, Zhejiang University, Hangzhou 310029 )
The damaged symptoms of 15 kind of fruit crops caused by acid rain and their sensitivity to it were studied. The results indicated: (1)The symptoms were mostly characterized by spots scattered among leaf veins. These spots had a chlorotic and water-soaked appearance with vague boundaries during tieir initial stage of development. Spot color varied with kinds of fruit crops and might be dark brown, reddish brown, gray white, etc. Severe injury could lead to perforation at the spotted areas or even leaf drop. (2) Different kinds of fruit crops showed different sensitivity to acid rain stress. If the cell membrane permeability was used as the injury index when the Eberhart-Russell model was applied, kiwi fruit, plum, mume and peach was rated as the most sensitive trees, and grape and cherry the sub-sensitive ones, while fig, citrus, chestnut, jujube, apple, peach and loquat were comparatively insensitive. (3)The threshold pH value at which acid rain caused barely visible injury to leaves in most kinds of fruit crops was 2.5-3.0, and the pH 3. 5 may be considered the reference value for invisible injury.