Departmental Bulletin Paper ミズナラ実生の初期成長における生育条件の影響と葉の生理的応答

津田, 元  ,  小野, 清美  ,  隅田, 明洋  ,  原, 登志彦

0073pp.57 - 64 , 2015-03-31 , 北海道大学低温科学研究所 = Institute of Low Temperature Science, Hokkaido University
落葉広葉樹ミズナラは冷温帯林を構成する樹種の一つである. 林床のミズナラ実生の葉の展開時期には低温になることがあり, 未成熟葉は低温による光ストレスや, さらに上層木が落葉樹である場合には強光ストレスにさらされる可能性がある. 生育環境に応じた実生の初期成長や葉のストレス応答を明らかにするために, 光条件と温度条件を組み合わせてミズナラ実生を栽培した. 弱光高温では実生の相対成長速度が大きく, ストレス応答が少なかった. 弱光低温では葉の展開が遅く, 展開完了した葉の光合成速度が低かったが, 強光低温下のような実生の著しい成長阻害は見られなかった. また, 未成熟葉の光合成能力は低いが, ストレス応答系が働いて極端な光ストレスを防いでいることが示された.
Quercus crispula Blume is a deciduous species that is typically found in cool temperate forests. Its leaves expand in early spring, when plants in cool temperate forests are sometimes exposed to low temperatures of approximately 10℃. Immature leaves of Q. crispula could suffer from photo-oxidative stress under such low temperatures, even under low light intensity. Under deciduous canopy trees, it is likely that immature leaves of Q. crispula seedlings will receive high light and suffer from strong photo-oxidative stress. In this study,we grew Q. crispula seedlings from seeds in environmentally controlled chambers to investigate how the initial growth of seedlings is affected by different combinations of light and temperature,and how expanding immature leaves and expanded leaves respond to environmental stresses. Seedlings grown under low light with a high temperature had higher relative growth rates than those grown under the other conditions,and showed smaller stress responses. Our results suggested that this growth condition is favorable for Q. crispula seedlings. Under low light and low temperature, leaves expanded slowly and showed low photosynthetic rates and low F v/F m even after they had fully expanded. Seedling growth was strongly inhibited under high light and low temperature. Immature expanding leaves with low photosynthetic rates avoided photo-oxidative stress by various mechanisms including the water-water cycle, and maintained a relatively high F v/F m.

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