Size Distribution and Mineral Nutrients of Soybean Seeds in Response to Drought Stress

Accumulation of mineral nutrients in soybean seeds grown under drought stress may have a role in drought tolerance. Because drought stress reduces dry matter accumulation and seed size, drought stress may increase the concentration of mineral nutrients in soybean seeds and may decrease the content of nutrient per seed. The objective was to study the effect of drought on seed size distribution and whether different drought-stress patterns increase mineral nutrient concentration in soybean seeds similar in size. Two experiments were conducted, one in the greenhouse and one in the field. In the greenhouse experiment, three-drought stress treatments were imposed on soybean plants at beginning seed fill (R5) for 23–26 days: well-watered (WW), sudden severe stress (SS), and gradual stress (GS) imposed prior to severe stress. In the field experiment, irrigation and nonirrigation (rainfed) conditions were imposed on soybean plants at R5 for the entire seed filling period. Drought stress decreased seed size in the greenhouse experiment, but not in the field experiment. Within similar seed sizes, drought-stress treatments increased concentrations of phosphorus (P), potassium (K), calcium (Ca), molybdenum (Mo), manganese (Mn), copper (Cu), and zinc (Zn) in seeds above well-watered treatment, but this increase varied between the two experiments. This increase in nutrient concentrations in seeds from drought-stressed plants compared with well-watered plants for seeds similar in sizes indicates that the increase in nutrient concentration in seeds from drought-stressed plants is not necessarily due to a reduction in dry matter accumulation. Accumulation of minerals in seeds might be an important response in drought stress tolerance.