Physiological Variance of Soybean Under High Night Temperature Stress.

Projections showed that global warming is likely to increase 1.5-2 between 2030 and 2050 under current emission scenarios. At the same time that day temperatures increase, high night temperatures (nights with temperatures higher than 22will increase. Models predict that days with high night temperature will increase 40% by 2100. Studies have demonstrated the negative impacts of high temperature on soybean including reduced yield and seed size. However, no research has been done to demonstrate cultivar variability to high night temperatures in soybean. This experiment determined the physiological response of four soybean cultivars grown under high night temperature treatment of 30ºC by measuring photosynthesis, respiration, stomatal conductance, chlorophyll fluorescence, Vcmax. Jmax, seed yield, pod number, harvest index. Two cultivars were selected for their tolerance to high day temperature, and the other two for being sensitive to high day temperatures. A complete randomized block design with three replications was used in this experiment. Four cultivars of soybean were planted in the greenhouse at 26/22 day/night) until flowering stage (R2), then move the plants to the growth chamber with different temperature, high night temperature (32.3/32.3 day/night), and regular night temperature (32/21.6 day/night) for 14 days at Auburn University Plant Science Research Center from May to September 2019. Analysis of data showed that high temperature tolerant cultivar PI360846 and commercial cultivar AG48x9 have subtle influences from high night temperature. Yield decrease is not distinct in these two cultivars. High night temperature increased midday photosynthesis only in one of the tolerant cultivars. Seed yield decrease about 40% due to less pods and smaller pods in the sensitive cultivars. Vcmax, photosynthesis and respiration were lower in regular temperature.