Factors controlling the release of nitrogenous compounds from roots of soybean

Abstract

Abstract The release of nitrogenous (N) compounds from the root systems of legumes supplements the nitrogen requirements of associated cereals under mixed cropping systems. The mechanism of the release of these N compounds is not fully understood. We therefore investigated the factors that may possibly control the release of N compounds from the roots of soybean (Glycine max L. Merr. cv. Bragg). Treatment consisted of shoot detachment at the vegetative growth stage. In addition we compared the release of N compounds from roots of plants with detached shoots and intact plants. Shoot detachment resulted in the increase of the release of N compounds, but decrease in nitrogen fixation, root respiration, sugar and ATP concentrations. The rates of decrease in nitrogen fixation, root respiration, and ATP concentration were rapid within 2 h after treatment, while the rate of decrease in the sugar concentration was slower. Both root ATP concentration and the release of N compounds from plants with detached shoots were the largest around 8 and 24 h after treatment. Shoot detachment resulted in the increase in the amounts of ureides and amino acids in nodules. The release of N compounds was more closely related to the root ATP concentration than to the sugar concentration. It is suggested that the decrease in root ATP concentration may be involved in the release of N compounds from roots of legumes.