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

Rates of light-saturated net photosynthesis (P_Nmax) and darkrespiration (Rd) on a leaf area basis, leaf dry mass per area(LMA), leaf nitrogen content on a leaf area basis (LNa) andinstantaneous nitrogen use efficiency (NUE=P_Nmax/LNa) were followedduring leaf development in six evergreen broad-leaved tree speciestypical of warm-temperate forests in Japan. These species wereCastanopsissieboldii, Quercus myrsinaefolia, Quercus glauca, Machilus thunbergii,Cinnamomum japonicumandNeolitsea sericea.When expansion of leafarea was complete, P_Nmax was about one third of its peak valueand increased for another 15 to 44 d. Rd at full leaf expansionwas about 1.5 to 3.5-times greater than steady-state rates.These facts suggest that leaf development was still underwayat the time of full leaf area expansion. Low P_Nmax at full leafexpansion was caused both by low leaf nitrogen content and lowNUE. P_Nmax increased with the increase in LMA during leaf developmentin all six species; data from the literature for other specieswith different life forms also indicated a similar tendency.The steady-state LMA varied markedly among species. Becauseleaves with larger steady-state LMAs need more resources fortheir construction, they will also need longer periods for maturation.We hypothesized that the period required for the attainmentof peak P_Nmax, the ‘leaf maturation period’, dependson the steady-state LMA. Plotting data from the present studytogether with those from literature for other plants acrossseveral life forms showed a strong positive relationship betweenleaf maturation period and steady-state LMA, supporting thehypothesis.Copyright 1998 Annals of Botany Company. Castanopsis sieboldii, Cinnamomum japonicum,delayed period, expansion period, full leaf expansion,Machilus thunbergii,maturation period,Neolitsea sericea, Quercus glauca, Quercus myrsinaefolia,steady-state LMA.     

Changes in mesophyll anatomy and sink–source relationships during leaf development in Quercus glauca, an evergreen tree showing delayed leaf greening

Changes in mesophyll anatomy, gas exchange, and the amounts of nitrogen and cell wall constituents including cellulose, hemicellulose and lignin during leaf development were studied in an evergreen broad‐leaved tree, Quercus glauca, and in an annual herb, Phaseolus vulgaris. The number of chloroplasts per whole leaf in P. vulgaris increased and attained the maximal level around 10 d before full leaf area expansion (FLE), whereas it continued to increase even after FLE in Q. glauca. The increase in the number of palisade tissue cells per whole leaf continued until a few days before FLE in Q. glauca, but it had almost ceased by 10 d before FLE in P. vulgaris. The radius and height of palisade tissue cells in Q. glauca, attained their maximal levels at around FLE whereas the thickness of the mesophyll cell wall and concentrations of the cell wall constituents increased markedly after FLE. These results clearly indicated that, in Q. glauca, chloroplast development proceeded in parallel with the cell wall thickening well after completion of the mesophyll cell division and cell enlargement. The sink–source transition, defined to be the time when the increase in daily carbon exchange rate exceeds the daily increase in leaf carbon content, occurred before FLE in P. vulgaris but after FLE in Q. glauca. During leaf area expansion, the maximum daily increase in nitrogen content on a whole leaf basis (the maximum leaf areas were corrected to be identical for these species) in Q. glauca was similar to that in P. vulgaris. In Q. glauca, however, more than 70% of nitrogen in the mature leaf was invested during its sink phase, whereas in P. vulgaris it was 50%. These results suggest that Q. glauca invests nitrogen for cell division for a considerable period and for chloroplast development during the later stages. We conclude that the competition for nitrogen between cell division and chloroplast development in the area of expanding leaves can explain different greening patterns among plant species.