Investigation of Physiological Responses of Different Soybean Cultivars Under Drought Stress

Soybeans with modified fatty acid compositions are widely used to improve oil quality and develop functional food products; however, physiological responses to drought stress during early growth stages remain insufficiently understood. This study compared shoot and root responses of three soybean cultivars with contrasting fatty acid profiles: Osoy (elevated linolenic acid; OS), PE529 (elevated oleic acid; PE), and Pungsannamul (PS) under drought stress conditions. Drought significantly reduced plant height, shoot biomass, and leaf area in all cultivars, although the magnitude of reduction differed among genotypes. PS exhibited the greatest decreases in plant height (39%), shoot dry weight (47%), and leaf area (78%) compared with well-watered conditions. In addition, PS showed relatively higher net carbon assimilation rate and stomatal conductance during the early phase of drought, but significantly lower values than OS and PE after 7-8 days of treatment, indicating a relatively higher sensitivity to drought stress. Root trait responses varied among cultivars. Total root length was largely maintained under drought conditions; however, all cultivars exhibited increased root distribution in deeper soil layers. Notably, PE showed a relatively higher proportion of roots at 40 cm depth. Whole-plant water use efficiency (wWUE) did not differ among cultivars under drought conditions; however, Pearson correlation analysis revealed strong associations between wWUE and root traits in PE, including total root length (r = 0.72), average root diameter (r = -0.77), and root volume (r = 0.65). Overall, PE exhibited relatively stable morphological and physiological responses under drought stress, suggesting a comparatively higher adaptive potential during early growth stages.