Impact of a 4.5-degree C Increase of Temperature and Elevated Carbon Dioxide on MG II, III, and IV Cultivars of Soybean.

Twenty-two cultivars of soybean in maturity groups II, III, and IV were grown in field soil in 2-m rows in four temperature gradient greenhouses at Gainesville Florida in the summers of 2005 and 2006.  Temperatures were either at a baseline (tracking continuously slightly above Gainesville ambient) or 4.5 degrees C above baseline.  Carbon dioxide concentrations were at either ambient concentrations in two of the greenhouses (about 380 ppm) or elevated concentrations in the other pair of greenhouses (700 ppm).  Water was applied 2 to 3 times a week with an automatic sprinkler irrigation system.  At the end of the growing period, plants were harvested as they reached physiological maturity for detailed components analysis of stems, pods (podwalls and seeds).  Percentage seed set and harvest index indicated that soybean was only slightly adversely impacted by this 4.5 degree C temperature increase.  This finding is in line with previous studies in controlled environment chambers of the cultivar ‘Bragg.’  These findings also indicate that most of the cultivars of soybean are much less sensitive to elevated temperatures than are many cultivars of rice, which might have implications for crop selections assuming that significant global warming occurs in the future.