Interaction of age and competition under CO2 enrichment

Typically, Andropogon virginicus L. (broomsedge, C-4) replaces Aster pilosus Willdenow (aster, C-3) in old-field succession in the North Carolina Piedmont, USA. The current work was designed to see how this situation may change under elevated CO2 concentrations in the future. Aster and broomsedge were grown in a modified deWit Replacement Series under 350, 500 and 650 mu l 1(-1) CO2. Aster was added to the pots 6 weeks after broomsedge emerged and all plants were harvested 6 weeks after aster emerged. The C-4 species, broomsedge, did not respond to CO2 enrichment, but leaf area and dry weight of the C-3 aster were greater at 650 than at 350 mu l 1(-1) CO2. Aster did not suppress established broomsedge plants at any CO2 level. After 6 weeks broomsedge reached a size where competition with aster seedlings did not delay its growth in controlled environments. Future increases in atmospheric CO2 concentrations may slow the rate of succession in old fields, but will not necessarily eliminate broomsedge from the composition of the perennial herbaceous community.