In long-term exposure to elevated CO2, adaptive responses may include changed phenological development that may or may not affect final size and reproduction. To elucidate if phenological development and final size of annual species is affected by selection at different [CO2], we grew Arabidopsis thaliana at pre-industrial, ambient, and elevated atmospheric CO2; 800 µE m-2 s-1 PAR in controlled environmental chambers. We used seeds from a previous selection experiment where Arabidopsis plants were selected for high seed yield at different [CO2] over 5 generations. The plants were grown at 22˚ C day: 18˚ C night. Phenological stages were recorded thought the plant life as well as rosette diameter, leaf numbers, and length of the inflorescence during reproduction and yield.
Plants grown in low CO2 developed more slowly than plants grown at ambient or elevated CO2 although plants that had previously selected at pre-industrial CO2 grew faster than plants pre-selected at elevated CO2. This impact of selection under CO2 and growth CO2 on phenological pattern was consistent with observed trends of rosette diameter and leaf number. As expected, rosette diameter in pre-industrial CO2 was significantly depressed compared to growth in ambient or elevated CO2, which were similar. These data suggest that plants have already adapted to increasing atmospheric CO2 and little adaptation is expected in the future.