Analyses of ionic compositions of acid rain in the San-in districts and studies on effects of simulated acid rain on growth and physiology of trees.

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The amount of precipitation, pH values of rain water, and ionic compositions were continuously monitored from April, 1990 to December, 1991 in the Hiruzen forest of the Tottori University Forests in the San-in districts. The pHs tended to be lower corresponding with the rise Of SO_4 ion. The amount of nss (not from sea salts) -SO_4^<2-> was comparatively high in early winter and in April.Effects of simulated acid rain solutions (SO_4^<2-> : NO_3^- = 1 : 1) on growth, dry weight increment, and ethylene production in seedlings of woody species were investigated. Application of the pH 1.6 solution to the shoot system of plants for 2 months significantly decreased biomass of Larix leptolepis, Ulmus davidian, and Pinus densiflora seedlings. Treatments with other solutions including pH 2.6, 3.6, and 4.6 had no significant effects on dry weight increment of all of these species.Application of the pH 1.6_solution to the soil surface for 3 months significantly decreased the biomics of potted Cryptomeria japonica and Chamaecyparis obtuse seedlings. Dry weight reduction was more drastic in seedlings planted in sand or decomposed granite than in andisol.Effects of sulfuric acid solutions on growth, dry weight increment, and production of plant growth regulators in seedlings of woody species were also investigated. Application of the 5mM/I solution (PH 2.10) to the shoot system of plants with a hand spray for 2 months significantly decreased growth and biomass of C. japonica, C. obtusa, P. densiflora, Betura Platyphylla, and Ulmus americana seedlings. The 5mM/1 solution also enhanced ethylene production in these species. The IAA content in needles or leaves was significantly reduced in ptomeria, Chamaecyparis, Pinus, and Betura by the application with 5, 0.5, and 0.05 mM/l solutions. The ABA content was not affected by acid application.