Photosynthetic response of seedlings of the sub-tropical tree Schima superba with exposure to elevated carbon dioxide and temperature

Seedlings of Schima superba were exposed to both ambient (375 ppm) and 720 ppm levels of CO2 in combination with two incubation temperatures (25/20, 30/25 degrees C, day/night) for a six-month period. Net height growth of seedlings was enhanced in the early period of exposure to high levels of CO2. However, when seedlings were exposed for a longer period of time to this high concentration, net height growth was inhibited. Decreased photosynthetic rate with elevated CO2 was observed when measured in the ambient CO2 over a long-term exposure of 6 months. In contrast, a significant increase in photosynthesis was noted for seedlings exposed to higher incubation temperature in either ambient or 720 ppm CO2 concentrations. The response of CO2 assimilation to internal Ci was indicated by the lower sensitivity in seedlings grown in elevated CO2 concentration. Though this response could also be found in a higher sensitivity in seedlings grown at higher temperature, the seedlings grown in normal conditions (ambient CO2 and temperature) were still more sensitive to CO2 assimilation response to internal Ci. This experiment suggests that: (1) exposure of seedlings to higher CO2 levels for longer periods may lead to a decrease in seedling height growth and photosynthetic rate, as well as decreasing sensitivity to changing internal CO2 concentrations; (2) the optimum temperature for photosynthesis of seedlings grown in an elevated CO2 concentration was higher than that for seedlings grown in ambient concentration. (C) 1999 Elsevier Science B.V. All rights reserved.