Research Plant Physiologist USDA-ARS Raleigh, North Carolina
Body of Abstract: High temperatures can reduce soybean productivity and seed quality, as demonstrated in moderate, long-term temperature elevation as well as short, severe heat stress experiments. However, high temperature response variation among genotypes had yet to be investigated in open-air field conditions. To test the hypothesis that soybean responses to elevated temperature will vary among genotypes, we measured the physiological and agronomic responses of ten soybean genotypes to a 4 °C above ambient air temperature increase during the seed fill period. Plants grew in the ground and in open air conditions, to realistically mimic an agronomic setting. We found that physiological and seed composition responses to elevated temperature varied among genotypes and among the three years of the field study. While daytime photosynthesis and nighttime respiration were increased by elevated temperature under some conditions, both respiration and the maximum velocity of carboxylation by Rubisco acclimated after the first week of exposure to elevated temperatures. Critically, the economically important seed oil concentration was usually reduced by elevated air temperature during the seed fill period, and seed protein responses to temperature were highly variable. This experiment demonstrated variability in soybean germplasm for high temperature responses in a controlled, open-air field experiment, and suggests that soybean seed composition responses to high temperature could be improved through breeding or biotechnology.