Effect of nodulation with Bradyrhizobium japonicum and Shinorhizobium fredii on xylem sap composition of Peking (Glycine max L. Merr.)

An experiment was conducted to analyze the differences in the nitrogenous compounds originating from symbiotic nitrogen fixation between soybean (Glycine max L. Merr.) cv. Peking inoculated with slow-growing Bradyrhizobium japonicum USDA110 (Hup(+)) and fast-growing Shinorhizobium fredii USDA193 (Hup(-)). The distribution of N in the nitrogenous compounds in the xylem sap showed that ureides accounted for 80, 78, and 85%, followed by asparagine for 4.3, 8.3, and 3.8%, and glutamine for 1.9, 3.5, and 1.3% of the total N in Peking (at the pod-setting stage) inoculated with USDA110 and USDA193, and Akisengoku (at the flowering stage) inoculated with A-1017, respectively. The distribution of asparagine and glutamine in the xylem sap of Peking inoculated with USDA193 was significantly higher than that of both cultivars inoculated with slow-growing rhizobia (p = 0.05) although the distribution of nitrogenous compounds other than amides did not show an appreciate difference among the three kinds of symbiosis. The results obtained in this experiment suggest that the main forms of transport of nitrogenous compounds in the xylem sap of soybean plants were ureides, regardless of the inoculated rhizobial species or genera, S. fredii and B. japonicum. Peking inoculated with fast-growing S. fredii USDA193 produced a relatively large amount of asparagine and glutamine compared to Peking inoculated with slow-growing B. japonicum USDA110.