| Summary: | 碩士 === 國立屏東科技大學 === 森林系 === 92 === Cinnamomum brevipedunculatum, Symplocos shilanensis, Anneslea fragrans and Magnolia kachirachirai are all rare and endemic tree species in Taiwan. In order to understand their ranges of physiological tolerance to temperature and light, the photosynthetic light responses and temperature responses of both sun and shade leaves of these species were determined in summer and winter at Nanjenshan forest.
Results showed that the optimum temperature for photosynthesis (T-opt) in both sun and shade leaves of all 4 species had significant seasonal acclimation abilities. Optimum temperatures were higher in the summer (27.5-30.4℃) and declined in the winter (22.2-24.6℃) for all species. T-opt in sun and shade leaves decreased 5-6℃ and 2-3℃, respectively. In addition, sun leaves showed higher T-opt than shade leaves in the summer but the reverse occurred in the winter. Among the 4 species, T-opt of S. shilanensis was 2-3℃ lower than those of the other 3 species in both seasons. Furthermore, S. shilanensis also showed wider range of temperature for optimum photosynthesis than the other 3 species. Sun leaves of all the species had higher net photosynthetic rate at optimum temperature (A-opt) than shade leaves when they were compared in the same season. However, there were no seasonal differences for A-opt either in sun leaves or in shade leaves of each species.
Results for photosynthetic light responses showed that sun leaves of the 4 species had higher net photosynthetic rates than shade leaves when light intensities were higher than 100 µmol m-2s-1. On the contrary, shade leaves showed higher photosynthetic rates than sun leaves at lower light conditions. There were no significant differences in photosynthetic light saturation points (LSP) between sun and shade leaves of each species. In addition, there were no significant seasonal differences in LSP of sun leaves of each species either. Sun leaves of all species but M. kachirachirai had higher dark respiration rates than shade leaves. A. fragrans showed distinctively higher light compensation point (LCP) in sun leaves (26.1 µmol m-2s-1) than in shade leaves (4.8 µmol m-2s-1). From the light responses measured in the summer, light saturated photosynthetic rates (A-sat) in sun leaves of all 4 species were not high, ranging only from 5.73 to 7.24 µmol m-2s-1 and no significant differences among them. In addition, A-sat of sun leaves in the 4 species showed no seasonal differences. As for morphological characteristics, single leaf areas in shade leaves of the 4 species were significantly larger than those in sun leaves, while leaf mass per area was higher in sun leaves than in shade leaves.
In conclusion, the 4 species in this study showed seasonal acclimation abilities in optimum temperature for photosynthesis. S. shilanensis had lower optimum temperature (22℃) during winter season, indicating that it can be rehabilitated in areas of lower temperature conditions than the other 3 species. In addition, the A-sat values of all the 4 species were relatively low, indicating that they are all shade-tolerant species.
|
|---|
