Morphological and physiological responses of Siebold's beech (Fagus crenata) seedlings grown under CO2 concentrations ranging from pre-industrial to expected future levels

摘要

Siebold's beech (Fagus crenata) is a common species in the cool temperate forests of Japan. As the natural regeneration of beech forests is expected to contribute to forest conservation in future, we investigated the effects of different CO2 concentration ([CO2]) on the growth of beech seedlings in relation to morphology and physiological changes. Acorns collected from beech forest in Minakami, central Japan were germinated and grown during a first growing season of six months under four [CO2] levels (200, 350, 550, and 750 μL L^[-1]). Stem mass increased with increasing [CO2]; however, root mass did not change significantly among the treatments. With increasing [CO2], net photosynthetic rate (Pn) and leaf area increased, whereas transpiration (Tr), stomatal conductance, leaf chlorophyll content, and leaf longevity decreased. Although water use efficiency (WUE; i.e., Pn/Tr) improved with increasing [CO2], the density of stomata did not significantly change. Increases in the number of bud and the terminal bud length with increasing [CO2] indicated accelerated formation of additional branches and leaves in the next season. At high [CO2] environment in future, improved WUE may be nevertheless advantageous for the survival of beech seedlings preferring mesic conditions.