Abstract: In the symbiotic system of actinorhizal plants and Frankia, nitrogenase activity is closely relied on the photosynthetic products of plants. To approach this physiological relativity, we have synchronously examined the photosynthetic rate, N₂ase activity, NH₄⁺, reducing sugar and total nitrogen contents in the nodules of the same plant of Alnus tinctoria Sarg at different time during the day. The results indicated that the maximum of N₂ase activity appeared behind the maximum of photosynthetic rate. This suggested that it was photosynthetic products that influenced the N₂ase activity, and the transport of the products from leaves to nodules took a certain time. In the nodules, when NH₄⁺ and redu cing sugar contents decreased, the N₂ase activity increased and at the meanwhile, the total nitrogen content increased too. These phenomena had been discussed. It can be con cluded that reducing sugar as the derivatives of photosynthetic products influences immediately on nitrogen fixation and can provides not only the energy for nitrogen fixation, but also the carriers for NH₄⁺ which was the first product of nitrogen fixation.

Key words: Photosynthesis, Nitrogen fixation, Alnus tinctoria