Effect of Day and Night Temperatures During Floral Induction on Morphology of Soybeans1

Abstract

AbstractTemperature affects the vegetative and reproductive morphology of soybeans [Glycine max (L.) Merrill]. Descriptive information of the effects of temperature will assist in development of a dynamic simulation model. The purpose of this study was to determine the effects of day and night temperatures on growth and development of the determinate soybean cultivar ‘Ransom’. Seedlings were grown under a long‐day (non‐inductive) photoperiod at 26/22 C day/night temperatures in a temperature controlled greenhouse until the expansion of the first trifoliolate leaf. Plants then were moved into five controlled‐environment chambers programmed for 9‐hour photoperiods with temperature regimes of 14/10, 18/14, 22/18, 26/22, and 30/26 C. At the beginning of each night, groups of plants were moved from the five day temperatures to each of the five night temperatures to obtain a total of 25 day/night temperature combinations. Significant interactions between day and night temperatures for all measured characteristics except branch internode length made general evaluations of simple effects of day and night temperatures difficult. Instead, responses to the specific combinations of day/night temperature were considered. At the conclusion of 50 consecutive short days, area per leaf and vegetative dry weight were greatest at 26/10 C temperatures while pod dry weight was greatest at the higher night temperature combination of 26/22 C. The lowest net carbon dioxide exchange rate was obtained at temperatures of 14/26 C, and the highest rates at 26/14 and 26/18 C. The extent of apical dominance, given as the ratio between main stem height and total branch length, was greatest for plants from either warm day and warm night or cool day and cool night combinations. Warm night temperatures, in conjunction with any of the day temperatures, shortened the time from first exposure to inductive photoperiod to anthesis. At the four coolest day/night temperature combinations (14/10, 14/14, 18/10, and 18/14 C) pods were not formed even though floral initiation had occurred