The Growth Responses of Soybean Plant to Photoperiod and Temperature : I. Responses in vegetative growth

Abstract

An early cultivar "Wase-Furisode" was used as a material plant. Characters of vegetative growth under the combinations of two photoperiods (LD: 14 hr, SD: 9 hr) and five temperature regimes (day-night, 35/30, 30/25, 25/20, 20/15, and 15/10°C) were compared both at the same chronicle date (the 16th day of treatments, A-plot) and at the same growth stage (6.5 trifoliate stage, B-plot). The results are summarized as follows: 1) Both shedding of cotyledons and flowering were hastened as the temperature increased, but the former occurred at the two trifoliate leaf stage and the latter at the stage of five trifoliate, in spite of the different earliness under different conditions. 2) At A-plot, stem height, leaf area, and total dry weight per plant increased with increasing temperatures and under LD condition. Nodule weight was greatest at 30/25° and decreased with decreasing temperatures. Leaf appearance rates increased with increasing temperatures and were greater under LD than under SD at lower temperatures. Water content (%) and SLW of lamina increased with decreased temperatures, the former being higher under SD and the latter under LD than under the respective opposed day-lengths. Lamina to stem ratio had a tendency to increase at lower temperatures and was greater under SD. Top to root ratio increased with increased temperature, being little affected by photoperiod. 3) At B-plot, the qualitative characters such as SLW, lamina to stem ratio, top to root ratio changed similarly as at A-plot, but water content of lamina decreased with decreasing temperatures. Stem height and mean internode length reached a maximum at 25/20° under LD, but increased with increasing temperatures under SD. Leaf area reached a maximum at 30/25°, while total dry weight, stem weight per 1 cm length tended to increase with decreasing temperatures, being very small at 35/30°. Nodule weight per plant and nodule size became greater as the temperature decreased. In general, branching occurred more abundantly and at lower nodes as the temperature decreased. 4) At A-plot, RGR had the keen correlations with both RLGR and NAR (r=0.978 and r=0.960, respectively), but at B-plot it correlated strongly only with RLGR (r=0.967). Correlations between total dry weight and nodule weight (r=0.920), roots weight and nodule weight (r=0.921) were also very strong at B-plot. 5) From the results obtained, it may be concluded that the optimum temperatures for vegetative growth of soybean plant are 30-35° day temperature or 32-33° mean daily temperature.