SLOW LEAF DEVELOPMENT OF EVERGREEN BROAD-LEAVED TREE SPECIES IN JAPANESE WARM TEMPERATE FORESTS

Rates of light-saturated net photosynthesis (P N max) and dark respiration (Rd) on a leaf area basis, leaf dry mass per area (LMA), leaf nitrogen content on a leaf area basis (LNa) and instantaneous nitrogen use eciency (NUE fl P N max}LNa) were followed during leaf development in six evergreen broad-leaved tree species typical of warmtemperate forests in Japan. These species were Castanopsis sieboldii, Quercus myrsinaefolia, Quercus glauca, Machilus thunbergii, Cinnamomum japonicum and Neolitsea sericea. When expansion of leaf area was complete, P N max was about one third of its peak value and increased for another 15 to 44 d. Rd at full leaf expansion was about 1‐ 5t o 3‐5times greater than steady-state rates. These facts suggest that leaf development was still underway at the time of full leaf area expansion. Low P N max at full leaf expansion was caused both by low leaf nitrogen content and low NUE. P N max increased with the increase in LMA during leaf development in all six species; data from the literature for other species with dierent life forms also indicated a similar tendency. The steady-state LMA varied markedly among species. Because leaves with larger steady-state LMAs need more resources for their construction, they will also need longer periods for maturation. We hypothesized that the period required for the attainment of peak P N max, the ‘leaf maturation period’, depends on the steady-state LMA. Plotting data from the present study together with those from literature for other plants across several life forms showed a strong positive relationship between leaf maturation period and steady-state LMA, supporting the hypothesis. # 1998 Annals of Botany Company