Evaluation of N2 fixation by stem and root nodules in sesbania rostrata during rainy and dry months

Abstract

Sesbania rostrata is the most popular green manure legumes in Tamilnadu, India.S. rostrata produces both stem and root nodules. Until this time, no experiments had been performed to assess the superiority of one kind of nodule over the other. The levels of nitrogenous compounds, like nitrite, nitrate, total nitrogen, free amino acids, total soluble proteins, total allantoin, total allantoic acid, and total ureides, were determined in both the stem and root nodules during rainy and dry seasons. During the rainy season, the stem nodules possessed heavy deposition of these N-containing compounds than the root nodules. On the other hand, during the dry season, the root nodules accumulated substantial levels of these nitrogenous compounds. In a similar way, the activities of nitrogenase and nitrate reductase were higher in stem nodules during the rainy season, and the trend was reversed during the dry season, the root nodules having more nitrogenase and nitrate reductase. In consonance with the higher activities of enzymes and gorging of nitrogenous compounds, calorific values were more in the stem nodules during the rainy season. The activities of oxygen scavenging enzymes were higher in stem nodules during the dry season, possibly indicating their role in alleviation of H2O2 and O 2 - city to the nodules. As regards rhizobial population, the root nodules always contained moreRhizobia than that of the stem nodules. The efficiency of the stem and root nodules to fix more nitrogen and synthesize nitrogenous compounds is seasonal. In the dry season, the entire role of N2-fixation seemed to be borne by root noduleRhizobia only, since stem nodules during this period are hardly formed and sparsely distributed.