PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Optimal leaf nitrogen content of an evergreen understorey plant in a temperate climate. Onno Muller^{*,1, 2}, Kouki Hikosaka², Niels Anten¹, Marinus Werger¹, Tadaki Hirose², ¹ Utrecht University, dept. of Plant Ecology, Utrecht, Utrecht, The Netherlands² Tohoku University, Sendai, Miyagi, Japan

ABSTRACT- In a temperate climate, evergreen species in the understorey are exposed to large seasonal changes in light and temperature. We determined for one year every month the photosynthetic traits of an evergreen understorey shrub Aucuba japonica in three different light regimes: understories of temperate and evergreen forests, and in a gap. Low temperature and high PFD had similar effects on photosynthetic acclimation: higher nitrogen and rubisco contents per leaf area, higher chlorophyll a/b and rubisco/chlorophyll ratios and a lower chlorophyll/nitrogen ratio. Multiple regression analyses indicated that PFD has a stronger effect on photosynthetic traits when the leaf is developing, while temperature has a stronger effect after leaf development. The leaf nitrogen content was closely correlated with photosynthetic capacity, as was the amount of the photosynthetic enzyme rubisco in the leaf. The relationship between leaf nitrogen content and photosynthesis changed per month dependent on PFD and temperature. The optimal leaf nitrogen content for maximum photosynthesis per unit nitrogen was calculated. There was a strong correlation (r²=0.51) between the measured leaf nitrogen contents and the predicted optima. This research shows that the photosynthetic apparatus acclimates to both PFD and temperature and that the increase of leaf nitrogen content in the winter has not only a storage function but also increases photosynthesis both per unit leaf area and per unit nitrogen.

KEY WORDS: photosynthetic acclimation, evergreen, optinal leaf nitrogen content, seasonality