Response of C4 (maize) and C3 (sunflower) crop plants to drought stress and enhanced carbon dioxide concentration

Sunflower (Helianthus annuus L.) and maize (Zea mays L.) were chosen as C3 and C4 crop plants and assessed for the impact of enhanced CO2 (700 ppm) and its interaction with drought stress in open top chambers (OTCs). The ameliorative effect of higher CO2 concentration (eCO2) under drought stress was quantified. It is interesting to note that the C3 crop responded significantly and positively with eCO2 under both well-watered and drought stress treatments for root: shoot ratio while C4 crop showed a better response only with the drought stress environment. Root volume showed a positive significant response with CO2 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 eCO2 showed an ameliorative effect leading to higher Pn 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 eCO2 and drought stress environments. The study confirmed the beneficial effect of eCO2 in maize and sunflower by ameliorating the adverse affects of drought stress.