The response of plants to carbon dioxide (CO 2 ) enrichment is an important aspect to be thoroughly investigated in order to accurately predict the impact on resource use as well ecosystem level responses. But the extent of response of individual plant species is dependent on the underlying biotic and abiotic stresses. In the current project, the response of Cenchrus ciliaris, a C4 grass, was investigated under CO 2 enrichment conditions under nutrient stress. Eco-physiological growth parameters were assessed within two plastic chambers with one chamber kept at ambient CO 2 conditions (500ppm) and the second enriched with CO 2 (1000ppm). Three treatments were studied: ambient (ACO2), enriched (ECO2) and alternating (alternating two weeks in each chamber; ALCO2). High atmospheric CO 2 concentrations did increase shoot and inflorescence production under nutrient stress. The blade area of ECO2 plants was significantly larger than that of ALCO2 plants on the 31st of March 2010 at P=0.06 and on the 7th of April 2010 (P=0.074). Stomatal density of C.ciliaris, however, did decrease for ECO2 and ALCO2. Under ACO2, average sheath biomass was signcantly higher under nutrient stressed condition than under non-stressed condition (65.81% vs. 52.96%; respectively). Growth allocations results revealed a rush toward reproductive production for ECO2 under nutrient stress conditions.