The relationship between light-saturated photosynthetic capacity
(Pmax) 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 Pmax 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., H. Kobayashi, S. Inoue, and K. Gyokusen., and Obsahuje bibliografii
Spatial and temporal variations in light-saturated photosynthetic capacity and needle nitrogen (N) content were investigated in one
8 m tall Japanese cedar (Cryptomeria japonica D. Don) canopy for a full year. The photosynthetic capacity and needle N content in various layers of the canopy were measured every month. Temporal variations in photosynthetic capacity and needle N content expressed on a projected-area basis (Parea, Narea) were similar. Furthermore, both Parea and Narea decreased with increasing depth from the top of the canopy on each sampling date. As a consequence, a significant correlation was observed between Narea and Parea. Temporal variations in photosynthetic capacity and needle N content expressed on a mass basis (Pmass, Nmass) were also similar. Pmass also decreased with increasing canopy depth. However, in contrast to Narea, there was only a slight decrease in Nmass with increasing canopy depth. Hence, the correlation between Nmass and Pmass was lower than the projected-area value. Because Narea was highly correlated with the needle mass per projected-area (NMA), the spatial variation in Narea (and therefore Parea) in the canopy is attributed to the variation in NMA, which decreases as the depth from the top of the canopy increases. Furthermore, the slope of the linear regression between Narea and NMA differed between sampling dates, indicating that the temporal variations in Narea (and therefore Parea) are strongly influenced by Nmass. For most of the sampling dates, a linear regression between Narea and Parea tends to converge into a single line segment. However, on several sampling dates, there was a pronounced decline in Parea below this line segment. This reduction in Parea, which does not accompany a reduction in Narea, seems to be attributable to stomatal limitations induced by the low soil temperature in winter and early spring. and H. Kobayashi, S. Inoue, K. Gyokusen