| Summary: | 碩士 === 國立屏東科技大學 === 森林系所 === 99 === In Hengchun area of southern Taiwan, the dry season lasts from November of each year to mid May of the next year. This research compared the seasonal variations, from dry season to rainy season, of predawn water potential (PWP) and photosynthetic capacity (Acap) in ten tree species, including nine saplings of native tree species and one invasive species, Leucaena leucocephala. These results would provide information on the physiological and morphological responses to prolonged water deficiency of these tested species. Field measurements showed that sapling of Pittosporum pentandrum did not suffer water stress since its PWP during dry season (December 2009 to May 2010) was only -0.09 MPa less than during rainy season; PWP of L. leucocephala and Melanolepis multiglandulosa decreased only -0.47 MPa, while PWP of Gelonium aequoreum, Broussonetia papyrifera, Planchonella obovata, and Hibiscus tiliaceus decreased -0.63 to -0.89 MPa. On the other hand, PWP of Ehretia resinosa, Allophylus timorensis, and Aglaia formosana dropped at least -1.35 MPa, indicating that these species experienced severe water stress. All tested species showed significantly lower Acap in dry season than in rainy season. Comparing the measurements of Acap during dry season versus rainy season in each species, P. pentandrum could maintain at around 88%; L. leucocephala and M. multiglandulosa could maintain at above 70%; M. multiglandulosa, E. resinosa, B. papyrifera, and A. timorensis showed above 60%; yet Acap of P. obovata, G. aequoreum, and A. formosana in dry season had only half of their Acap in rainy season, showing that their physiological activities were obviously inhibited. During the dry season, some leaves in saplings of E. resinosa, and more than half of the leaves in saplings of B. papyrifera and A. timorensis, would turn yellow and fall, while the other 7 species remain green. Overall, P. pentandrum could still maintain similar physiological performances in dry season as compared to in rainy season, but A. formosana physiological activities was significantly decreased in dry season. The invasive species, L. leucocephala, maintained its water potential and photosynthetic capacity during dry season at relatively higher levels, exhibiting its strong competitive capability.
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