© 2007 Heron Publishing—Victoria, Canada
Photosynthetic capacity and nitrogen partitioning in foliage of the evergreen shrub Daphniphyllum humile along a natural light gradient
Shin-Ichiro Katahata (1, 2), Masaaki Naramoto (1), Yoshitaka Kakubari (1) and Yazuru Mukai (1, 3, 4)
1. Department of Forest Resources, Faculty of Agriculture, Shizuoka University, Ohya 836 Shizuoka 422-8529, Japan / 2. Present address: Department of Science of Biological Environment, United Graduate School of Agricultural Science, Gifu University,
Yanagido 1-1, Gifu, 501-1193, Japan / 3. Present address: Department of Environment Science, Faculty of Applied Biological Sciences, Gifu University, Yanagido 1-1,
Gifu, 401-1193, Japan / 4. Corresponding author (ymuka@gifu-u.ac.jp) / Received August 22, 2005; accepted January 20, 2006; published online November 1, 2006
Summary
We examined the effects of leaf age and mutual shading on the morphology, photosynthetic properties and nitrogen (N) allocation
of foliage of an evergreen understory shrub, Daphniphyllum humile Maxim, growing along a natural light gradient in a deciduous Fagus crenata-dominated forest in Japan. Seedlings in high-light environments were subject to greater mutual shading and 1-year-old foliage
survival was lower than in seedlings in low-light environments, indicating that the survival rates of foliage were related
to the degree of mutual shading. Although specific leaf area (SLA) in current- and 1-year-old foliage was curvilinearly related
to daily photosynthetic photon flux (PPF), SLA was unaffected by leaf age, indicating that foliage in D. humile may not acclimate morphologically to annual changes in light caused by mutual shading. Light-saturated net photosynthetic
rates (Pmax) were correlated with daily PPF in current-year foliage. In addition, a strong, positive relationship was found between nitrogen
concentration per unit leaf area and Pmax. In contrast, the relationship among PPF, N and photosynthetic parameters in 1-year old foliage was weak because of the strong
remobilization of N from older leaves to current-year foliage in plants growing in high light. However, the relationship between
daily PPF and both photosynthetic N-use efficiency and the ratio of maximum electron transport rate to maximum carboxylation
rate did not differ between current-year and 1-year-old foliage, suggesting that these responses help maintain a high photosynthetic
efficiency even in older foliage. We conclude that D. humile maximizes whole-plant carbon gain by maintaining a balance among photosynthetic functions across wide ranges of leaf ages
and light environments.
Keywords:
irradiance, nitrogen, photosynthetic acclimation, photosynthetic nitrogen-use efficiency (PNUE), ribulose-1, 5-bisphosphate
carboxylase/oxygenase (Rubisco).
