Some growth-related parameters, such as specific leaf mass (SLM) (referred to as dry weight (DW)), leaf area and soluble protein content, were determined in primary leaves of sunflower plants grown for 42 days under ambient atmospheric CO2 (400 L L−1) or elevated CO2 (800 L L−1) concentrations (Fig. 1). In both treat- ments, leaf area increased up to 32 days, especially in the plants grown under elevated CO2 concentrations. SLM referred to as DW peaked at 22 days in the plants grown under ambient atmospheric CO2 concentrations, but at 16 days in the plants grown under elevated CO2 concentrations, decreasing later during leaf develop- ment in both treatments (Fig. 1A and B). A significant decrease in the soluble protein content was observed during aging of sunflower primary leaves at both CO2 levels (Fig. 1C).
The plants grown in the presence of elevated CO2 concentra- tions exhibited lower chlorophyll a and b contents and carotenoids than those grown under ambient atmospheric CO2 conditions (Fig. 2). Leaf aging reduced the photosynthetic pigment content under both treatments of CO2. Thus, total chlorophyll content decreased by about 65% between 22 and 42 days in plants grown at elevated CO2 concentrations, but only by 46% in those grown under