Acclimation of leaf characteristics of Fagus species to previous-year and current-year solar irradiances

To examine the effects of different solar irradiances on leaf characteristi cs at the leaf primordium and expansion stages, we shaded parts of branches in the upper canopies of two adult beech trees, Fagus crenata Blume and Fa gus japonica Maxim., for 4 years. The treatments during the leaf primordium and leaf expansion stages, respectively, were: (1) high light and high lig ht (H, control), (2) high light and low light (I-IL), (3) low light and low light (LL), and (4) low light and high light (LII). Both number of cell la yers in palisade tissue and individual leaf area were affected by the previ ous-year irradiance, whereas cell length of palisade tissue was larger in L H leaves than in LL leaves, suggesting determination by current-year irradi ance. Lamina chlorophyll/nitrogen ratio was higher in HL and LL leaves than in LI-I leaves, suggesting determination by current-year irradiance. Diurn al minimum values of lear water potential measured under sunlit conditions were lower in H and LH leaves than in HL and LL leaves. Effective osmotic a djustment was found in H and LH leaves, suggesting that leaf water relation s were affected by current-year irradiance. Net photosynthetic rate and sto matal conductance measured under sunlight conditions were higher in H and L H leaves than in I-IL and LL leaves. Thus, effects of current-year irradian ce had a greater effect on leaf-area-based daily carbon gain than previous- year irradiance.