Distribution of Total non-structural Carbohydrates in Soybean Plants at Stages of Development

Abstract

Five varieties of soybeans were grown in the summer of 1979 and in the spring of 1980. Concentrations of total non-structural carbohydrates (TNC) were determined in different plant fractions harvested at intervals of development. Leaf blade TNC was consistently higher in the spring than in the summer crop, presumably the results of environmental influences. Rapid decline in leaf TNC during pod filling and the low concentrations (2-3%) in the abscised leaves suggested the redistribution of assimilates. Stems, petioles and pod walls were also sites of stored carbohydrates to meet the demands of developing seeds. In some cases, the presence of abundant TNC in pod walls at R4 stage, along with the decrease of TNC in vegetative organs implied possible requirement of stored energy for the differentiation and growth of pod walls. Translocation from pod walls to seeds was more conspicuous in late (R6-R8) than in early (R4-R6) seed-filling period. Changes of root and nodule TNC were correlated with those of dinitrogen-fixing activity as previously reported. Compared with other varieties, Shih-Shih and Kaohsiung No. 3 maintained relatively high TNC concentrations in roots ad nodules during the reproductive phase which coincided with higher activities of dinitrogen fixation. The early-maturing Shih-Shih was characterized by high TNC levels in leaf blades and stems, especially in the spring crop season.