High Day‐ or Nighttime Temperature Alters Leaf Assimilation, Reproductive Success, and Phosphatidic Acid of Pollen Grain in Soybean [Glycine max (L.) Merr.

Abstract

ABSTRACTSoybean [Glycine max (L.) Merr.] is often exposed to high daytime and nighttime temperatures during critical growth stages. Threshold mean daily temperature for photosynthesis, respiration, and reproductive process in soybean is ≥26°C. In future, the magnitude of increase in nighttime temperatures will be greater than in daytime temperatures. The objectives were to determine effects of high daytime or nighttime temperatures on (i) leaf photosynthetic and respiration rates; (ii) pollen germination, pod‐set, and seed weight; and (iii) pollen phospholipids profile. Soybean plants were exposed to high daytime temperature (39/20°C), high nighttime temperatures (30/23°C, 30/26°C, and 30/29°C), or optimum temperature (30/20°C) for 10 d at flowering stage. High daytime temperature (39/20°C) or nighttime temperatures (30/29°C) increased leaf respiration rates and decreased leaf chlorophyll content, photosynthetic rate, photochemical quenching, and electron transport rate compared to optimum temperature. Likewise, high temperature decreased pollen viability and germination. Lower pollen germination at high temperature may be due to decreased levels of saturated phospholipids and phosphatidic acid in pollen grains compared with optimum temperature. Pod‐set and seed weight were decreased by high daytime or nighttime temperature. In conclusion, high daytime (39/20°C) or nighttime (30/29°C) temperature decreased leaf photosynthetic rate and pollen germination, leading to lower pod‐set and seed weight.