Temperature Affects Drought Tolerance Mechanisms In Soybean and Its Wild Ancestor Glycine Soja.

During drought, the stomata of soybean plants close in response to low soil water potential. Consequently, they lose their capacity to assimilate carbon and yield is decreased. One way for a plant to avoid severe drought is to conserve soil water by slightly decreasing transpiration when it senses moderate stress in the aerial or soil environment. This mechanism can be triggered in the leaves during times of high vapor pressure deficit (VPD; i.e. afternoons) or also in the roots as the soil dries. Current efforts to improve drought tolerance in soybean have involved exploring genetically diverse germplasm. Glycine soja (soja) is a wild species related to soybean, which is adapted to dry regions of Northern China.  The objectives of this research were to 1) identify possible drought tolerance mechanisms in the leaves and roots of soja and 2) determine whether these mechanisms were influenced by temperature. Experiments measuring transpiration response to vapor pressure deficit (well-watered) and experiments measuring transpiration response to soil drying were conducted on soybean and soja genotypes in controlled environment chambers at 25, 30, and 35 °C. The transpiration response differed significantly between soybean and soja and among genotypes within each species. Some soybean genotypes decreased transpiration with increasing VPD, but it was dependent on temperature. Soja did not decrease transpiration under VPD stress at any temperature. Soja did, however, decrease transpiration in response to soil drying earlier than soybean. While soja does not appear to be a source for leaf-based drought tolerance traits, these results suggest that it may possess root traits that are beneficial in drought environments.