Growth and Photosynthetic Responses of Seedlings of Japanese White Birch, a Fast-Growing Pioneer Species, to Free-Air Elevated O3 and CO2

Plant growth is not solely determined by the net photosynthetic rate (A), but also influenced amount of leaves as a apparatus. To evaluate responses to CO2 and O3, we investigated effects elevated (550–560 µmol mol?1) O3 (52 nmol mol?1; 1.7 × ambient O3) on photosynthesis biomass allocation in seedlings Japanese white birch (Betula platyphylla var. japonica) grown free-air exposure system without any limitation root growth. Total was enhanced decreased O3. The ratio shoot (R:S ratio) showed no difference among treatment combinations, suggesting that neither nor affected leaf. Accordingly, might be more important for response birch. Based A measured under respective conditions, light-saturated at light intensity 1500 m?2 s?1 (A1500) young (ca. 30 days old) exhibited enhancement August, acclimation CO2. However, lower A1500 observed old 60 plants (regulated twice O3). Conversely, light-limited 200 (A200) significantly leaves, suppressed leaves. Decreases total attributed accelerated leaf senescence indicated reduced A200 Increases high intensities, which possibly occurred before and/or limiting intensities.