The results showed that the lower the density the higher the net photosynthesis was per plant. However, the higher the net photosynthesis per unit area was, the higher was the density. Further, the lower the density, the higher the rate of dark respiration per plant. Due to this evidence the differences of gross photosynthetic rate per unit area reached 9.24, 7.70 and 6.04 g CO2 m-2h-1for high, medium and low density, respectively. As affected by different photosynthetic rate, the higher density the higher the dry matter production per unit area. Moreover, different plant population densities are characterized by different vertical distributions of dry matter production. The vertical distribution of 13C-labeled amounts in leaves indicated the difference of assimilatory capacity within the canopy. Based on distribution of 13C labeled amounts, the photosynthetic rate by layers were estimated and the results showed that the upper-most layer was the highest. The present experiment suggested that the different leaf distributions and light attenuation within the canopy have limited the photosynthetic capacity of leaves in respective layers. © 1997, The Society of Agricultural Meteorology of Japan. All rights reserved.