Effects of Drought and Elevated Atmospheric Carbon Dioxide on Seed Nutrition and 15N and 13C Natural Abundance Isotopes in Soybean Cultivars Under Controlled Environments.

The objective of this research was to evaluate the response of soybean cultivars to the effect of drought and elevated temperature on seed composition and mineral nutrition. In a repeated growth chamber experiment, soybean cultivars Williams 82, maturity group, (MG) III and Hutchesson (MG V) were grown under greenhouse conditions until the beginning of seed-fill stage (R5), then trasferred to growth chambers until full maturity (R8). The plants were subjected to the following four treatments: grown irrigated and subjected to 360 µmol mol^-1 CO₂ concentration (ambient concentration); grown irrigated and subjected to 700 µmol mol^-1 CO₂ concentration; grown under drought and subjected to 360 µmol mol^-1 CO₂ concentration; and grown under drought and subjected to 700 µmol mol^-1 CO₂ concentration. The drought treatment was imposed by growing plants at a soil water potential of about -150 to -199 kPa. For irrigated plants, soil water potential was kept at about -15 to -20 kPa. The results showed that in both cultivars drought alone or drought with elevated CO₂ resulted in an increase in seed protein and oleic acid, but a decrease in total oil, linolenic acid, sucrose, glucose, and fructose concentrations. However, raffinose and stachyose showed an increase under drought and drought with elevated CO₂. Elevated CO₂ alone or drought with elevated CO₂ resulted in a decrease in N, P, K, B, and Zn. No consistent trend for seed Cu, Fe, Mg, and Mn. Seed  𝛿 ¹⁵N (¹⁵N/¹⁴N ratio) and 𝛿 ¹³C (¹³C/¹²C ratio) natural abundance isotopes were altered under drought or drought with ambient or elevated CO₂ concentrations, indicating changes in source of nitrogen and nitrogen and carbon metabolism.  The presentation will highlight further understandings of the effects of drought and elevated CO₂ on seed nutrition and provide breeders with useful information on seed quality selection.