Response of C 4 (maize) and C 3 (sunflower) crop plants to drought stress and enhanced carbon dioxide concentration

Sunflower ( Helianthus annuus L.) and maize (Zea mays L.) were chosen as C 3 and C 4 crop plants and assessed for the impact of enhanced CO 2 (700 ppm) and its interaction with drought stress in open top chambers (OTCs). The ameliorative effect of higher CO 2 concentration (eCO 2 ) under drought stress was quantified. It is interesting to note that the C 3 crop responded significantly and positively with eCO 2 under both well-watered and drought stress treatments for root: shoot ratio while C 4 crop showed a better response only with the drought stress environment. Root volume showed a positive significant response with CO 2 concentration enhanced over ambient level and the increment in root volume was 146% and 340% in sunflower and maize crops, respectively. The leaf water potential, stomatal conductance and transpiration showed a decreasing trend in both the crops with drought stress and eCO 2 showed an ameliorative effect leading to higher P n rates in sunflower crop under drought stress treatment. The findings reveal that improvement of root traits is worth attempting for the future crop behavioral responses under eCO 2 and drought stress environments. The study confirmed the beneficial effect of eCO 2 in maize and sunflower by ameliorating the adverse affects of drought stress.