Damage and Yellow or Dark Brown Discoloring of Various Garden Plants, Vegetables and Trees Exposed to the Atmosphere Containing Boron Compounds in an Artificial Exposure Chamber

Various species of vegetables, garden plants and trees were exposed to the containing boron compounds in an exposure chamber. The tips of the leaves of all species were damaged and became yellow or dark brown discolored. The situation was the same as the actual plant damage that occurred in previous polluted areas. The damage appeared fastest in mulukhiya followed by lettuce, eggplant, mini-tomato, tomato, green pepper and strawberry among the vegetables, rudbeckia followed by mum, pansy, blue salvia, salvia, lily, hydrangea, cockscomb, angelonia, madagascar periwinkle and balloon flower among the garden plants, and fastest in lauraceae followed by Japanese aucuba, Japanese black pine, coral ardisia, white oak, redrobin and conifer for the trees. The concentration of boron at the tip of the damaged leaf was 900-7, 100 μg/g. The tip levels were 2.0-25 times higher than that in the rest of the damaged leaves, and 11-88 times higher than the concentration of in the non-exposure leaves. The boron compounds seem to be absorbed from the stomata of the leaves and carried by the transpiration stream to the tip. It can be considered that the boron concentration at the tip exceeds the maximum limit, and the leaves become discolored into yellow or dark brown at the tip. The mean accumulation rate of boron was the highest in vegetables followed by garden plants and trees. The mean rates were 290, 208 and 32 μg/g·day, respectively. The damage tended to be more serious in plants with the higher accumulation rate.