Technical Abstract: Plant species vary in response to atmospheric CO2-enrichment and differences in physiology, structure, and symbiotic relationships do not always reliably predict species responses, especially when grown in communities. Experiments examining effects of CO2-enrichment on plant communities are critical to further our understanding of ecosystem response to global climate change. A model regenerating longleaf pine ecosystem was exposed to two CO2 regimes (ambient, 365 'mol/mol and elevated, 720 'mol/mol) for three years using open-topped chambers. Total above- and belowground biomass was 70% and 49% greater, respectively, in CO2-enriched chambers; carbon (C) content followed a similar response pattern, resulting in a significant increase of 13.8 Mg C per ha under elevated CO2. Responses of individual species, however, varied. Longleaf pine (Pinus palustris) was primarily responsible for the positive response to CO2 enrichment. Wiregrass (Aristida stricta), rattlebox (Crotalaria rotundifolia), and butterfly weed (Asclepias tuberosa) exhibited negative above- and belowground biomass responses to elevated CO2, while sand post oak (Quercus margaretta) did not differ significantly between CO2 treatments; C content again followed patterns similar to biomass. Elevated CO2 resulted in alterations in community structure; 88% of total biomass in CO2-enriched plots was allocated to longleaf pine with only 8% allocated to wiregrass, rattlebox, and butterfly weed. In comparison, ambient CO2 plots allocated 76% of total biomass to longleaf pine but had 19% allocated to wiregrass, rattlebox, and butterfly weed. Therefore, while longleaf pine may perform well in a high CO2 world, other members of this community may not compete as well as atmospheric CO2 continues to rise. Despite variable species responses, the system gained 11.4 Mg C per ha under high CO2 suggesting that this ecosystem should be a sink for atmospheric CO2.