Nitrogenase and N2O Reductase Activities of Detached Nodules and Site Soils of Casuarina cunninghamiana and Alnus trabeculosa

Abstract:

To understand the activities of nitrogenase and N₂O reductase (Nos) for non-legume nitrogen-fixing tree species, the detached nodules, rhizospheric soil in nodule root grown area (RSI) and rhizospheric soil near nodule root grown area (RSN) were collected from Casuarina cunninghamiana and Alnus trabeculosa in Fujian Province, southeastern China, and the nitrogenase and Nos activities were determined by acetylene reduction method and acetylene inhibition technique, respectively. The results showed that the nitrogenase activity of detached nodules could be detected only under anaerobic condition, and the Nos activity only in aerobic condition. The nitrogenase activity in RSI and RSN under aerobic conditions was higher than those under anaerobic condition, and the Nos activities could be detected only under anaerobic condition. In aerobic condition, there was no significant difference in nitrogenase activity between RSI and RSN, while Nos activity of RSI was significantly larger than that of RSN. The nitrogenase activity were greater than Nos activity for the two tree species, except that there were no nitrogenase activity for the detached nodules under aerobic condition. The nitrogenase activity in the RSI under aerobic condition was significantly positively correlated with that in RSN. However, the nitrogenase activity in nodules under anaerobic condition was negatively correlated with that in RSI and RSN under aerobic condition, and the Nos activity in nodules under aerobic condition was also negatively correlated with that in RSI and RSN under anaerobic condition. These would lay a foundation for studying the effect and regulation of symbiotic nitrogen fixation system of tree species nodulated with Frankia on N₂O sink intensity.