Effect of different CO2 concentrations on physiological responses of fall-dormant alfalfa

To study the physiological changes process of three types of fall dormancy alfalfa under three CO2 concentration (700 μmol·mol-1, 550 μmol·mol-1 and control 350 μmol·mol-1) in open-top chambers during the whole growth period. The results showed that: the CO2 concentration higher, the chlorophyll content and the content of soluble sugar higher of the whole growth period. The chlorophyll content was increased by an average of about 11.49%, 6.00%; soluble sugar content was increased by an average of 52.01%, 38.82% with 700 and 550 μmol·mol-1 treatment. The MDA content decreased by an average of approximately 18.20%, 17.93% with 700 and 550 μmol·mol-1 treatment. The elevated CO2 concentration had a significant positive effect on the synthesis of proline content at flowering (P<0.05) and the rest of the time was inhibited. In summary, CO2 concentration had a significantly effect on physiological indices of alfalfa at the early flowering (P<0.05). The chlorophyll synthesis cumulative amount of UC-1465 (non-fall dormancy alfalfa) higher than Maverick (fall dormancy alfalfa) and ABI700 (semi fall dormancy alfalfa) under high CO2 concentrations. And high CO2 concentration is more favorable for Maverick (fall dormancy alfalfa), ABI700 (semi fall dormancy alfalfa) to accumulate soluble sugar and reduce MDA content, it is very likely to enhance the capacity of ease stress and osmotic adjustment.