This Is AuburnElectronic Theses and Dissertations

Soybean Phenotypic Variation Under High Night Temperature Stress




Shu, Tianchu

Type of Degree

Master's Thesis


Crop Soils and Environmental Sciences


Soybean is the fourth most important commodity crop globally grown on over 83.1 million acres in the United States. Crop yield is required to increase a 50% to satisfy the demand of a growing population that will increase to 10 billion by 2050. However, high day and night temperature could influence plant growth reducing crop yield. High day temperature was proved to negatively affect photosynthetic activity then decrease yield. People have developed soybean cultivars that were tolerant to high day temperature. However, there is no research exploring cultivar tolerance and sensitivity to high night temperature on soybean. Our objectives were: 1) Investigate the effects of different short-term high night temperature applied during the reproductive stage on soybean and study if there is cultivar variation; and 2) Identify physiological effects of long-term high night temperature stress during vegetative stages and determine if there are cultivar variation to high night temperature. To accomplish objective one, four cultivars were exposed to different high night temperatures: extremely high night temperature (EHNT): 32/32 ℃; moderate high night temperature (MHNT): 32/26℃; control night temperature (CNT): 32/20℃ day/night temperature at full flowering (R2) for 14 days to explore short time HNT effects on reproductive stage. To accomplish objective two, 9 soybean cultivars were exposed to high night temperature from the beginning of germination for 50 days to study HNT long-term effect on vegetative stage (Control: 30℃/20℃, EHNT: 30℃/30℃ day/night). In both experiments, measurements included: photosynthesis, respiration, chlorophyll content and fluorescence. We found that short time EHNT (32℃) did not affect photosynthesis and respiration rate in reproductive stage but decreased seed production in one cultivar, therefore finding yield cultivar variation to EHNT. MHNT did not negatively affect plant growth in any of the cultivars. Long-term EHNT (30℃) from vegetative stage decreased photosynthetic rate, stomatal conductance, chlorophyll content and the efficiency of PSII (Fv/Fm) but not changing respiration rate. Some cultivars showed tolerance to EHNT as null effect over the aboveground biomass. In cultivar CM422 and DS25-1, EHNT tolerance may be associated with photochemical efficiency of PSII (Fv/Fm). We concluded from these two experiments that higher light intensity and longer exposure time intensified negative effect of high night temperature stress. These findings open the possibility to breed for high night temperature tolerance, but more research needs to be done to better understand the physiological effects of high night temperature stress and which are the most important traits to acquire tolerance.