Soybean seed composition under high day and night growth temperatures

High diurnal temperatures often affect development of soybean [Glycine max (L.) Merr.], but little is known about the relative influence of high day and night temperatures on the chemical composition of the seed. This study was conducted to determine the effects of combinations of high day and night temperatures during flowering and pod set (R1–R5), seed fill and maturation (R5–R8), and continuously during the reproductive period (R1–R8) on soybean seed oil, protein, and fatty acid composition. Day/night temperatures of 30/20, 30/30, 35/20, and 35/30°C were imposed on the soybean cultivar Gnome 85 in growth chambers. The day/night temperature combinations during R1–R5 had little effect on the oil and protein concentration and the fatty acid composition of seed produced. As mean daily temperature increased from 25 (30/20) to 33 (35/30)°C during R5–R8 and 25 (30/20) to 33 (35/30)°C during R1–R8, and oil concentration decreased and protein concentration increased. Increased day temperature during R5–R8 and R1–R8, averaged across the two night temperatures, increased oleic acid and decreased linoleic and linolenic acids. When night temperature was increased at 30°C day temperature during R5–R8 and R1–R8, oleic acid decreased and linoleic acid increased. When night temperature was increased at 35°C day temperature during R1–R8, oleic acid increased, and linoleic and linolenic acids decreased. These results indicate the importance of high day and night temperatures during seed fill and maturation in the oil, protein, and fatty acid composition of soybean seed.