Effects of elevated carbon dioxide concentration and soil temperature on the growth and biomass responses of mountain maple (Acer spicatum) seedlings to light availability

Some shade-tolerant understory tree species such as mountain maple (Acer spicatum L.) exhibit light-foraging growth habits. Changes in environmental conditions, such as the rise of carbon dioxide concentration ([CO2]) in the atmosphere and soil warming, may affect the performance of these species under different light environments. We investigated how elevated [CO2] and soil warming influence the growth and biomass responses of mountain maple seedlings to light availability. The treatments were two levels of light (100% and 30% of the ambient light in the greenhouse), two [CO2] (392 µmol mol−1 (ambient) and 784 µmol mol−1(elevated)) and two soil temperatures (Tsoil) (17 and 22°C). After one growing season, we measured seedling height, root collar diameter, leaf biomass, stem biomass and root biomass. We found that under the ambient [CO2], the high-light level increased seedlings height by 70% and 56% at the low Tsoil and high Tsoil, respectively. Under the elevated [CO2], however, the high-light level increased seedling height by 52% and 13% at the low Tsoil and high Tsoil, respectively. The responses of biomasses to light generally followed the response patterns of height growth under both [CO2] and Tsoil and the magnitude of biomass response to light was the lowest under the elevated [CO2] and warmer Tsoil. The results suggest that the elevated [CO2] and warmer Tsoil under the projected future climate may have negative impact on the colonization of open sites and forest canopy gaps by mountain maple.