Photosynthesis-nitrogen relationship in a Hinoki cypress (Chamaecyparis obtusa) canopy: A comparison with Japanese cedar (Cryptomeria japonica)

The relationship between light-saturated photosynthetic capacity (P _max) and leaf nitrogen (N) content was investigated for one year in a 15-year-old Chamaecyparis obtusa canopy and was compared with a Cryptomeria japonica canopy previously described. The linear regression between P _max and leaf N content tended to converge toward a single line segment from July to January and in May for C. obtusa. The slope of the linear regression between P _max and leaf N content of C. obtusa was gentler than that of C. japonica. The smaller regression coefficient of C. obtusa may reflect species differences in nitrogen nutrition requirements between C. obtusa and C. japonica. A pronounced decrease in the slope of the linear regression lines due to low temperature was observed in February and March. During this period, P _max of C. obtusa declined more than that of C. japonica suggesting that C. obtusa is less tolerant to low temperatures than C. japonica.