Distribution of leaf nitrogen within sugi (Cryptomeria japonica D. Don) canopy growing at different positions on a slope

To examine the effect of nitrogen availability on leaf nitrogen distribution within sugi (Cryptomeria japonica D. Don) canopy, we studied the relationship between leaf nitrogen content and light intensity in seven-year old trees that were growing at different positions on a slope (upper, middle and lower slope). Nitrogen availability increased from the upper position to the lower position on the slope. Leaf nitrogen per area (N_A) decreased with increasing depth from the top of the canopy ; this was caused by the decrease in leaf mass per area (LMA). Leaves sampled from the upper, middle and lower positions on the slope had successively higher N_A at any one layer in the canopy. This was because leaf nitrogen per weight increased from the upper position to the lower position on the slope. N_A was linearly related to light intensity within the canopy at every position on the slope. The regression coefficient of the linear relationship between N_A and light intensity was similar for all positions on the slope. However, the y-intercept of the relationship increased with increasing nitrogen availability. This suggested that the distribution of leaf nitrogen within sugi canopy could be predicted from the light intensity within the canopy and the y-intercept by linear regression, and that the y-intercept could be determined by nitrogen availability.