Eco-physiological and biochemical traits underpin drought tolerance and yield stability in soybean (Glycine max L.)

Drought stress severely limits soybean productivity by impairing growth, physiological processes, and yield. This study evaluated the morpho-physiological, biochemical, and yield responses of three soybean genotypes (AGS 383, NCS 1, and BU Soybean-1) under control, moderate, severe, and extreme drought conditions to identify drought-tolerant genotypes. Drought significantly reduced plant growth, nodulation, dry matter, leaf area index, photosynthetic traits, chlorophyll content, and grain yield, with greater reductions under increasing drought severity. Among the genotypes, AGS 383 consistently performed best, producing taller plants, greater nodulation, higher biomass, larger leaf area index, higher photosynthetic rate (37.74 µmol m⁻ 2 s⁻ 1 under control), greater chlorophyll content, and the highest grain yield (2.21–1.30 t ha⁻ 1 from control to extreme drought). NCS 1 maintained relatively stable leaf water status, stomatal conductance, transpiration, and accumulated the highest proline under severe drought, indicating effective osmotic adjustment. BU Soybean-1 retained comparatively higher leaf number and relative water content but showed lower biomass, photosynthetic capacity, and grain yield. Grain yield was positively associated with photosynthetic rate, chlorophyll content, plant height, water uptake, seed number, and 100-seed weight. Overall, AGS 383 showed the greatest drought tolerance and yield stability, making it a promising genotype for drought-prone environments and soybean breeding.