Effects of light and nitrogen fertilization on photosynthesis and leaf nitrogen content in cryptomeria japonica sapling

Relationship between light-saturated photosynthesis and leaf nitrogen content was studied in Cryptomeria japonica D. Don saplings growing under different light and nitrogen supply. Both light-saturated photosynthesis per area (P_max-area) and leaf nitrogen per area (N_area) increased with increasing light and nitrogen supply. P_max-area was highly positively correlated with N_area. The slope of the linear regression between P_max-area and N_area was 1.67 μmol CO₂ g N^-1 s^-1, which was low compared to that for other conifer trees previously described. Light-saturated photosynthesis per mass (P_max-mass) did not increase with increased light, but increased with increasing nitrogen supply. P_max-mass was also positively correlated with leaf nitrogen per mass (N_mass), but the correlation coefficient was low. Since P_max-area was highly correlated with N_area regardless of whether variation in N_area was due to light or nitrogen supply, this suggested that N_area would be a good index of photosynthesis in Cryptomeria japonica.