open access

https://hdl.handle.net/2115/82278

Growth and Photosynthetic Responses of Seedlings of Japanese White Birch, a Fast-Growing Pioneer Species, to Free-Air Elevated O-3 and CO2

英語

biomass allocation

2021-06

MDPI

Forests

12(6)

675

Plant growth is not solely determined by the net photosynthetic rate (A), but also influenced by the amount of leaves as a photosynthetic apparatus. To evaluate growth responses to CO2 and O-3, we investigated the effects of elevated CO2 (550-560 mu mol mol(-1)) and O-3 (52 nmol mol(-1); 1.7 x ambient O-3) on photosynthesis and biomass allocation in seedlings of Japanese white birch (Betula platyphylla var. japonica) grown in a free-air CO2 and O-3 exposure system without any limitation of root growth. Total biomass was enhanced by elevated CO2 but decreased by elevated O-3. The ratio of root to shoot (R:S ratio) showed no difference among the treatment combinations, suggesting that neither elevated CO2 nor elevated O-3 affected biomass allocation in the leaf. Accordingly, photosynthetic responses to CO2 and O-3 might be more important for the growth response of Japanese white birch. Based on A measured under respective growth CO2 conditions, light-saturated A at a light intensity of 1500 mu mol m(-2) s(-1) (A(1500)) in young leaves (ca. 30 days old) exhibited no enhancement by elevated CO2 in August, suggesting photosynthetic acclimation to elevated CO2. However, lower A(1500) was observed in old leaves (ca. 60 days old) of plants grown under elevated O-3 (regulated to be twice ambient O-3). Conversely, light-limited A measured under a light intensity of 200 mu mol m(-2) s(-1) (A(200)) was significantly enhanced by elevated CO2 in young leaves, but suppressed by elevated O-3 in old leaves. Decreases in total biomass under elevated O-3 might be attributed to accelerated leaf senescence by O-3,O- indicated by the reduced A(1500) and A(200) in old leaves. Increases in total biomass under elevated CO2 might be attributed to enhanced A under high light intensities, which possibly occurred before the photosynthetic acclimation observed in August, and/or enhanced A under limiting light intensities.

学術雑誌論文

Version of Record

Creative Commons Attribution 4.0 International