Growth and Leaf Gas Exchange in Three Birch Species Exposed to Elevated Ozone and CO₂ in Summer
2012
Hoshika, Yasutomo | Watanabe, Makoto | Inada, Naoki | Koike, Takayoshi
We examined the effects of ozone and elevated CO₂ concentration in summer on the growth and photosynthetic traits of three representative birch species in Japan (mountain birch, Monarch birch, and white birch). Seedlings of the three birch species were grown in 16 open-top chambers and were exposed to two levels of ozone (6 and 60 nmol mol⁻¹ for 7 h per day) in combination with two levels of CO₂ (370–380 and 600 μmol mol⁻¹ for daytime) from July to October. No adverse effects of ozone were found in the Monarch birch or the white birch, but elevated ozone in summer reduced branch biomass and net photosynthesis, and accelerated leaf abscission, in the mountain birch. Elevated CO₂ promoted root development and thereby reduced the ratio of shoot dry mass (stem + branch) to root dry mass (S/R ratio) in the mountain birch and white birch. In contrast, there was no difference in dry mass between ambient and elevated CO₂ for the Monarch birch, due to downregulation of photosynthesis. Studies of the combined effect of CO₂ and ozone revealed that elevated CO₂ did not ameliorate the effect of ozone on mountain birch in late summer. In considering the ameliorating effect of CO₂ on ozone damage, it is necessary to take account of the species and the season.
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