Effects of carbon dioxide, oxygen, and light on nitrogen-fixing activities in Japan clover (Kummerowia StriataS.)

The effects of carbon dioxide, oxygen, and light on nitrogen fixation in Japan clover (Kummerowia striata S.) were examined by the acetylene-reduction method. Oxygen was essential for nitrogen fixation in this plant, and the supplementation of carbon dioxide or exposure to light during this time did not alter the rate of nitrogen fixation. Japan clover did not show nitrogen fixation under anaerobic conditions, but the fixation activity appeared when CO2 and light were simultaneously supplied to the system. The evolution of oxygen by photosynthesis could be a cause of enhancing the nitrogen fixation activity. Diurnal variation of nitrogen fixation in Japan clover was also investigated. The nitrogen fixation fluctuated in accord with the light intensity of the solar radiation.