Experimental Studies on the Effects of Ozone on Growth and Photosynthetic Activity of Japanese Forest Tree Species

Abstract

Ozone (O₃) is a main component of photochemical oxidants, and a phytotoxic anthropogenic air pollutant. In North America and Europe, the current concentration of O₃ has been shown to have significant adverse effects on vegetation. In this review, we summarize the experimental studies on the effects of O₃ on the growth and photosynthetic activity of Japanese forest tree species to understand the present knowledge and provide sound basis for future research toward the assessment of O₃ impacts on Japanese forest ecosystem. Since the 1990s, several Japanese researchers have conducted the experimental studies on the effects of ambient levels of O₃ on growth and physiological functions such as net photosynthesis of Japanese forest tree species. Although the sensitivity to O₃ of whole-plant growth is quite different among the species, it was suggested that the current ambient levels of O₃ in Japan are high enough to adversely affect growth and photosynthetic activity of Japanese forest tree species classified into high O₃ sensitivity group such as Japanese beech. The N load to soil has been shown to reduce the sensitivity to O₃ of Japanese larch and increase that of Japanese beech. To establish the critical level of O₃ for protecting Japanese forest tree species, therefore, it is necessary to take into account the N deposition from the atmosphere. There is little information on the combined effects of O₃ and other environmental factors such as elevated CO₂ and drought on growth and physiological functions of Japanese forest tree species. Therefore, it is necessary to promote the experimental study and accumulate the information on the combined effects of O₃ and any other abiotic environmental factors on Japanese forest tree species.