2005 年 60 巻 6 号 p. 1105-1108
The effects of O3 and /or chronic mild water stress on photosynthetic characteristics and leaf antioxidative systems of Fagus crenata seedlings were investigated. The seedlings were exposed to charcoal-filtered air or 60 nmol mol-1 O3 for two growing seasons. In each gas treatment, the seedlings were received 250 ml (well-watered) or 175 ml (water-stressed) of water at 3-day intervals during the growth period. The O3 significantly reduced net photosynthetic rate, Rubisco concentration and chlorophyll concentration without stomatal closure, and significantly increased ascorbate concentration in the leaves of the seedlings. On the other hand, the water stress significantly reduced net photosynthetic rate and stomatal diffusive conductance to water vapor without significant reductions in the concentrations of Rubisco and chlorophyll, and significantly increased glutathione concentration in the leaves of the seedlings. Significant antagonistic effects of O3 and water stress were detected on net photosynthetic rate of the seedlings in September and October. In conclusion, because chronic mild water stress induces not only stomatal closure, but also increase of leaf glutathione concentration, the extent of the negative effects of O3 on net photosynthesis of Fagus crenata is less under the water-stressed condition than under the well-watered condition.
