Differential Growth Responses of Wheat Seedlings to Elevated CO2

Intraspecific variations in wheat growth responses to elevated CO 2 was evaluated using 20 Iranian bread wheat ( Triticum aestivum L.) cultivars. The plants were grown in the modified Hoagland nutrient solution at a greenhouse until 35 days of age using two levels of CO 2 (~380 and 700 µmol mol –1 ). The shoot and root dry weights of the wheat cultivars exhibited average enhancements of 17% and 36%, respectively, under elevated CO 2 . This increase was associated with higher levels of chlorophyll a (25%), chlorophyll b (21%), carotenoid (30%), leaf area (54%) and plant height (49.9%). The leaf area (r = 0.69 ** ), shoot N content (r = 0.62 ** ), plant height (r = 0.60 ** ) and root volume (r = 0.53 * ) were found to have important roles in dry matter accumulation of tested wheat cultivars under elevated CO 2 concentration. However, responses to elevated CO 2 were considerably cultivar-dependent. Based on the stress susceptibility index (SSI) and stress tolerance index (STI), the wheat cultivars exhibiting the best response to elevated CO 2 content were ‘Sistan’, ‘Navid’, ‘Shiraz’, ‘Sepahan’ and ‘Bahar’, while the ones with poor responses were ‘Omid’, ‘Marun’, ‘Sorkhtokhm’ and ‘Tajan’. The findings from the present experiment showed significant variation among the Iranian wheat cultivars in terms of their responses to elevated air CO 2 , providing the opportunity to select the most efficient ones for breeding purposes.