Effect of Photoperiod on Development and Metabolism of the Biloxi Soy Bean

1. Biloxi soy bean plants with flower primordia initiated upon them were transferred to photoperiods of 8, 10, 12, 13, 14, 15, 16, and 18 hours. The development of these primordia and the flowering and fruiting responses of the plants were determined. 2. The plants transferred to photoperiods of 8 to 13 hours bloomed nearly simultaneously and all produced fruits. The yield of fruits on the 8 hour lot was somewhat less than on the 10, 12, and 13 hour lots. 3. Flowering on the 14 and 15 hour plants was later than on those of shorter photoperiod, the flowers were less numerous, and no fruits were formed. 4. No flowers opened on the 16 and 18 hour plants during the experiment. 5. When plants were transferred to a range of photoperiods after flower primordia were initiated it was found that the longest photoperiod on which fruit formation occurred was 13 hours and the shortest one on which no flowering took place was 16 hours. 6. Plants were grown for biochemical studies on 8, 13, and 16 hour photoperiods after initiation of flower primordia. A control lot was grown continuously on 16 hour photoperiods. The carbohydrate and nitrogen metabolism of these plants was determined at frequent intervals throughout the season. 7. At the end of the week's induction period the total nitrogen and soluble non-protein nitrogen were higher in the plants receiving 8 hour photoperiods than in the controls. Carbohydrates were lower than in the controls, with the exception of starch in the leaves which was higher. 8. The total nitrogen in both leaves and stems of the 16 hour transfers became similar to that of the controls and the 13 hour transfers approached the 8 hour ones as the season advanced. The soluble non-protein nitrogen showed the same relationship in the stems. There was an abrupt rise in the amount of ammonia in the leaves and stems of the 8 and 13 hour transfer plants when pods were just beginning to form. 9. The amount of soluble carbohydrates in the transfer groups seems to be correlated with the length of photoperiod. Starch accumulated in the leaves and stems of the 8 and 13 hour transfers when pods were beginning to form. 10. Two groups of plants with flower buds initiated upon them and subsequently grown at photoperiods just above and just below the critical showed progressive deviation from each other in their carbohydrate and nitrogen metabolism. Those grown below the critical became similar to plants grown on 8 hour photoperiod, while those above the critical became similar to plants that had been kept vegetative by growing them continuously on 16 hour photoperiod.