| Summary: | 碩士 === 國立嘉義大學 === 森林暨自然資源研究所 === 94 === The purpose of this study was to investigate the effects of different light intensities of understory on the growth of seedlings of Pongamia pinnata, Cerbera manghas, and Terminalia catappa in Shihu coastal Casuarina windbreaks.
After 13-month field test, the results revealed that all of three species seedlings treated with 100 % relative light intensity ( R/FR＝1.25 ) had the highest seedling height and net root diameter growth. The averaged seedling height and net root diameter growth of the seedlings were 62.58 ± 3.29cm and 1.72 ± 0.06cm for Pongamia pinnata; 107.93 ± 3.47 cm and 3.73 ± 0.11cm for Cerbera manghas; and 39.98 ± 2.20 cm and 1.40 ± 0.06 cm for Terminalea catappa, respectively. Seedlings of the three species grown under 100 ％relative light intensity ( R/FR=1.25 ) attained the highest biomass. The biomass seedlings of Pongamia pinnata, Cerbera manghas, and Terminalia catappa were 475.50 ± 42.26 g, 1532.00 ± 106.49 g, and 258.50 ± 29.70 g, respectively. On the other hand, there were highest enhancements in leaf area, LAR and SLA of seedlings grown under lowest light intensity. Whereas, the leaf area, LAR, and SLA of seedlings decreased as the light intensity increased.
Light intensity and R/FR had significant effect on the leaf tissues of seedlings. Ultrastructure of leaves of the 3 species showed that when the leaves were grown under 100 % relative light intensity, it became thicker, the palisade tissue turned slim and tight, and the stomata became elliptic. Under low light intensity, the leaves became thinner, the palisade tissue turned short with large gaps, and the stomata became compressed. The number of stomata decreased as the light intensity increased. The results from chlorophyll study revealed that all of the seedlings of 3 species grown under low light intensity had the highest chlorophyll a, chlorophyll b and chlorophyll a+b contents in leaves. The chlorophyll a contents in leaves of Pongamia pinnata, Cerbera manghas, and Terminalia catappa were 3.07 ± 0.34 μg/g, 2.72 ± 0.18 μg/g, and 2.05 ± 0.12 μg/g, respectively. The chlorophyll b contents in leaves of Pongamia pinnata, Cerbera manghas, and Terminalia catappa were 1.24 ± 0.12 μg/g, 1.04 ± 0.08 μg/g, and 0.75 ± 0.04 μg/g, respectively. The chlorophyll a+b contents in leaves of Pongamia pinnata, Cerbera manghas, and Terminalia catappa were 4.32 ± 0.47 μg/g , 3.76 ± 0.26 μg/g, and 2.77 ± 0.16 μg/g, respectively.
The seedlings grown under 100 % relative light intensity had the highest compensation point, light saturation point and maximum photosynthesis rate. The compensation point, light saturation point, and maximum photosynthesis rate of the seedlings were 24.05μmole photon m-2s-1, 1800μmole photon m-2 s-1, and 22.16μmole CO2 m-2s-1, respectively for Pongamia pinnata; 40.13μmole photon m-2 s-1, 1800μmole photon m-2 s-1, and 19.93μmole CO2 m-2s-1, respectively for Cerbera manghas; are 33.51μmole photon m-2s-1, 1800μmole photo m-2 s-1 and 19.68μmol Co2 m-2 s-1, respectively for Terminalia catappa.
This study demonstrated that seedlings of Pongamia pinnata, Cerbera manghas, and Terminalia catappa, with characteristics of fast-growing under high light intensity and good adaptation to low light intensity, were promising tree species for reforestation of coastal windbreaks in Taiwan.
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