Some negative results of simulative acid mist and ozone treatments to Cryptomeria japonica D. Don seedlings in explanation of mature : C. japonica decline in the Kanto plains in Japan

Abstract

On experiment 1, simulated acid rain of sulfuric acid at pH 2.0, 3.0, 4.0, and 7.5 were sprinkled to two-year-old potted Cryptomeria japonica D. Don seedlings during four months. On experiment 2, simulated acid mist of sulfuric, hydrochloric, and nitric acids at pH 2.5, 3.5, and 7.5 were sprayed to two-year-old potted clone seedlings for three to five times a week during six weeks. On experiment 3, same mixed acids in experiment 2 at pH 2.5, 3.5, 4.5, and 7.5 were sprayed for three times a week with 0.1ppm O_3 exposure for five hours a day to two-year-old potted seedlings during 12 weeks. On experiment 4, high concentration of O_3 (0.5, 1/0, 2.0, and 3.2ppm) exposed to one-year-old potted clone seedlings for three hours after treatment of same simulated mixed acids mist in experiment 2 during five weeks. Visible injuries did not occer on pH 3.5 and 4.5 mist treatments, and on conbination of pH 2.0 mist and ozone treatments in experiment 2, 3, and 4. Dry matter production and fine root growth were decreased with decreasing pH of simulated acid rain and the effect of pH was markedly in pH 2.0 in experiment 1. Net photosynthesis and stomatal conductance were slightly increased in pH 3.5 and 4.5 mist treatments and these increases were accelerated markedly by the conbination of pH 2.5 mist and ozone treatments. Annual reports from air pollution obervatories in Japan suggests that NO_2 was almost constant leval (0.020-0.028ppm) from 1970 to 1990, and SO_2 was decreasing gradually from 0.057ppm to 0.010ppm for the period of 25 years before 1990 around Tokyo bay, one of the highly polluted area in Japan. The highest concentration of O_3 in a year was 0.39ppm in 1975, however, less than 0.23ppm in 1990 in Japan. These tendencies in decreasing air pollutions were allmost the same in the Kanto plains. Annual mean pH of wet deposition was 4.3-5.6 in Japan, and the mean values of pH were constant in resent year. From our experiments and the status of air pollution and wet deposition on the Kanto plains in Japan, we can not elucidate the causes of C. japonica tree decline in wet deposition and air pollution.