Ozone-induced reduction in the whole-plant dry mass of high-fertilised Fagus crenata seedlings was offset by the increase in leaf area, although the exposure to ozone decreased net photosynthetic rate.
To clarify the effects of ozone (O-3) on the growth of Fagus crenata seedlings under different soil nutrient conditions, seedlings were grown for two growing seasons under nine treatments comprised of a combination of three levels of gas treatments (charcoal-filtered air or O-3 at 1.0 or 1.5 times ambient concentration), with three levels of soil nutrient treatments (non-fertilised or a supply of relatively low or high concentrations of compound fertiliser). Significant interactive effects of O-3 and nutrient supply to soil on net photosynthetic rate, area of first-flush leaves, and the whole-plant dry mass were detected during the second growing season. The O-3-induced reduction in dry mass was observed in the non- and low-fertilised seedlings, but not in the high-fertilised seedlings. However, the extent of O-3-induced reduction in net photosynthetic rate was higher in the low- and high-fertilised seedlings than in the non-fertilised seedlings. Although the O-3-induced reduction in the leaf area was detected in the non- and low-fertilised seedlings, leaf area of the high-fertilised seedlings tended to be increased by the exposure to O-3. Therefore, O-3-induced reduction in the whole-plant dry mass of the high-fertilised seedlings is considered to be offset by the O-3-induced increase in the area of first-flush leaves during the second growing season. To accurately assess the effects of O-3 on dry matter production of F. crenata, the modification of the sensitivity to O-3 due to soil nutrient conditions must be taken into consideration.