Technical Abstract: Carbon sequestration in soils could mitigate atmospheric carbon dioxide (CO2) increases. Studies were conducted on elevated CO2 and temperatures effects on accumulation of soil organic carbon (SOC) and nitrogen (SON) by forages growing on previously cultivated land. Two subtropical species, bahiagrass (BG) and rhizoma perennial peanut (PP), were grown in field plots at baseline-ambient, +1.5, +3.0, and +4.5C in four temperature-gradient greenhouses, two each at 360 and 700 ppm CO2. The top 20 cm of soil was sampled in February 1995 and December 2000 before and after the project. The BG accumulated more SOC than PP across the six years, 1.40 and 0.75 g/kg, respectively. Mean SOC gains of BG at 700 and 360 ppm CO2 were not different (1.45 and 1.34 g/kg, respectively), but mean SOC gains of PP were greater in 700 than 360 ppm (0.95 and 0.54 g/kg, respectively). Temperatures of +3.0 and +4.5C caused SOC gains to decrease. Relative SON increases were similar to SOC. Conversion to forage from cultivation caused SOC to accumulate especially by BG. Elevated CO2 promoted accumulation of SOC in PP but not in BG. Elevated temperature decreased accumulations of SOC. Subtropical forage species gain SOC similarly to reports of other species.