DINITROGEN FIXATION, UREIDE CONCENTRATION IN XYLEM EXUDATE AND TRANSLOCATION OF PHOTOSYNTHATES IN SOYBEAN AS INFLUENCED BY POD REMOVAL AND DEFOLIATION

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Effects of pod removal and defoliation on the growth, dinitrogen-fixing activity, ureide concentration in xylem exudate and nodules, and translocation of photosynthates in soybean (Glycine max (L.) Merr. cv. Tamahomare) were examined and the following results were obtained. 1) Dinitrogen-fixing activity decreased significantly by both pod removal and defoliation. 2) The concentration of sugars and starch in the nodules increased by pod removal but decreased by complete defoliation, while it did not change by partial defoliation. 3) The ureide concentration in the xylem exudate and nodules increased by pod removal, especially by complete defoliation. 4) Pod removal led to a decrease in the export rate of ^<14>C from leaf but had no effect on ^<14>C distribution percentage in the nodules. 5) Exudation rate of ureide-^<14>C in the xylem sap was lower during the first hour after the exposure to ^<14>CO_2 and thereafter it was higher in depodded than in control plants. From these results, it is suggested that the factor controlling of the dinitrogen-fixing activity of soybean under ordinary field conditions is presumably not the status of the photosynthate supply to the nodules but, the export rate of the fixed-N from nodules.
社団法人日本土壌肥料学会の論文