Tadahiko Furuya

Influences of high night temperature on flowering and pod setting in soybean

Abstract Soybean (Glycine max (L.) Merr. cv. Enrei) plants were grown in pots (15-L volume) placed in a greenhouse with ventilation. At the time when the first flower opened, pots were transferred to growth chambers with natural lighting under day temperature of 30°C and night temperatures of 20, 25 or 30°C. The numbers of flowers opened and pods set each day were recorded and the seed yield and yield components were investigated after harvest. The increase in night temperature decreased the seed size and increased the number of flowers and pods. As a result, the seed weight per plant was unaffected by night temperature. However, high night temperatures increased the number of flowers on the secondary and tertiary racemes. These flowers opened after the 18th day of the flowering period and showed a high rate of pod setting. These results suggest that a high night temperature stimulated flower opening and pod setting in the secondary and tertiary racemes. The increases in the numbers of flowers and pods could serve to moderate the reduction of seed yield caused by a high night temperature.

Effects of carbon dioxide enrichment during different growth periods on flowering, pod set and seed yield in soybean

Abstract The objective of this study is to elucidate the effects of CO2 enrichment during different growth periods on flowering, pod set and seed yield in soybean (Glycine max (L.) Merr.). Soybean cultivar‘Fukuyutaka’was grown in a growth chamber of the Institute of Bioresources Research Center of Kyushu Electric Power Co., Inc. at Saga, Japan (33°17’-N, 130°18’-E) under natural light. The CO2 concentrations were maintained at 350 µmol mol−1 for ambient CO2 and at 700 µmol mol−1 for CO2 enrichment. CO2 concentration was elevated during the whole growth period (WP), vegetative growth period (VP) or reproductive period (RP). Seed yield was increased by CO2 enrichment during RP or WP due to the increase of pod number, but not by CO2 enrichment during VP.Although CO2 enrichment had no effect on the number of flowers, CO2 enrichment during RP increased the pod number on all raceme orders and that during WP increased the pod number in the secondary and tertiary racemes. It is suggested that an increase of seed yield by CO2 enrichment is mostly brought by the improvement of pod set, mainly on the high-order racemes that opened later during flowering period, and that the response of seed yield to CO2 enrichment is mainly attributed to the response during RP.