8. Watanabe, M. , Yamaguchi, M., Matsumura, H., Kohno, Y. and Izuta, T. (2008) Effects of ozone on growth and photosynthesis of Castanopsis sieboldii seedlings grown in different nitrogen loads. Journal of Agricultural Meteorology, Vol. 24, No. 3. 143-155
Abstract
To obtain basic data for evaluating the critical levels of ozone (O3) for protecting Japanese evergreen broad-leaved tree species, we investigated the effects of O3 on the growth and net photosynthesis of Castanopsis sieboldii seedlings grown under different nitrogen (N) loads. Two-year-old seedlings were grown in 12 experimental treatments, which were comprised of four gas treatments (charcoal-filtered air and three levels of O3 at 1.0, 1.5 and 2.0 times the ambient concentration) in combination with three N treatments (0, 20 and 50 kg ha-1 year-1) in open-top chambers during the two growing seasons. The net photosynthetic rate and the whole-plant dry mass of the seedlings were reduced by exposure to O3, while were increased by N load. No significant interaction between O3 and the N load for the whole-plant dry mass of the seedlings was observed. The N load increased the sensitivity of net photosynthetic rate to O3 during the first and second growing seasons. However, the increase in the area of second-flush leaves during the second growing season compensated for the O3-induced reduction in the net photosynthetic rate of the seedlings grown under relatively high N load. We concluded that the N load to the soil at ≤50 kg ha-1 year-1 has no influence on the sensitivity of the whole-plant dry mass of C. sieboldii seedlings to O3. Based on the relationship between AOT40 (accumulated exposure over a threshold of 40 nmol mol-1) of O3 during the daylight hours from April to September and the whole-plant dry mass increment per one growing season, the critical level of O3 for C. sieboldii, which was expressed as AOT40 for one growing season and corresponding to a 5% reduction in the whole-plant dry mass increment, was evaluated as 22 µmol mol-1 h.
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最終更新：2008年09月28日 08:30
