Slow Leaf Development of Evergreen Broad-leaved Tree Species in Japanese Warm Temperate Forests

Abstract

Rates of light-saturated net photosynthesis (PNmax) 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 efficiency (NUE=PNmax/LNa) were followed during leaf development in six evergreen broad-leaved tree species typical of warm-temperate forests in Japan. These species wereCastanopsis sieboldii, Quercus myrsinaefolia, Quercus glauca, Machilus thunbergii, Cinnamomum japonicumandNeolitsea sericea.When expansion of leaf area was complete, PNmax was about one third of its peak value and increased for another 15 to 44 d. Rd at full leaf expansion was about 1.5 to 3.5-times greater than steady-state rates. These facts suggest that leaf development was still underway at the time of full leaf area expansion. Low PNmax at full leaf expansion was caused both by low leaf nitrogen content and low NUE. PNmax increased with the increase in LMA during leaf development in all six species; data from the literature for other species with different 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 PNmax, 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.