Chemo-ecological Studies on Plant Indicators for Low Level Air Pollution

Abstract

The effects of low level air pollution on Japanese Cedar (Cryptomeria japonica) have been studied in the surrounding area of two thermoelectric power stations newly constructed in a rural area, Fukui Prefecture, on the Japan Sea side of central Honshu, Japan. The degree of visual injury in Japanese Cedar, scored with six different categories, was examined in 1974and 1977 respectively, covering the entire study area. A more complete monitoring has been conducted at eight permanent sites in Awara-cho since 1974. A dendrochronological study was also carried out to evaluate the effects of air pollution on the increment growth of Japanese Cedars. There were clear correlations between the distance from the power station and tree decline (Figs.3 and 15). Severe damage was observed, in general, within a 7 km radius from the power station. The localized injury of Japanese Cedar, along the flood plain of the two rivers, was also demonstrated (Fig.4). A rapid increase of injury was noted until through the late 1970's (Fig.5). The growth inhibition, during this period, was also revealed by tree ring analysis (Fig.14). Some recovery of tree vigor and increment growth was observed after the introduction of pollution control systems at the power station (Figs.5 and 14). Consistent relationships were demonstrated between the index of increment growth, i. e., standardized ring index, and the levels of SO₂ and NO₂ (Fig.17). Scarcely any correlation was observed between pH of rain water and the standardized ring index (Fig.16). Decreased levels of foliar tannin were observed in the Japanese Cedars growing in the polluted areas. The inhibition of the shikimate pathway, by air pollution, was suggested by biochemical studies. Increased predation damage was observed in the foliage of Japanese Cedars with low tannin levels. The predisposed effects of air pollution were discussed with special reference to the inhibition of the shikimate pathway.