In P. maximum the cumulative dry biomass production in two cuttings showed an increase of 59.24% and 43.17% in open top chambers (OTC) with elevated CO₂ (600±50 ppm) (C₆₀₀) and without elevated CO₂ (C_OTC) respectively over the open field grown corps (Ca). In S. hamata the dry matter increased by 39.79% under C₆₀₀ and 31.02% in C_OTC over Ca. The canopy photosynthesis (P_N x LAI) increased significantly in both the crop species with elevated CO_2. The increased rate of canopy photosynthesis indicated that there was higher assimilation of CO₂, which has intern maximum biomass production. The increase in fresh and dry matter accumulation in C₆₀₀ indicating that these crop species should be promoted for higher biomass production and carbon sequestration in the semi arid tropical environmental conditions.