本研究比較在葉溫28℃, CO2濃度365μ1L^(-1)的測定條件下,生長在充分日照環境下的30種台灣原生闊葉樹陽葉在雨季與乾季時的光合作用率,藉以建立其氣體交換潛力的資料。此30樹種在6月雨季初期測得的光飽和光合作用率在5.5~25.7μmol m^(-2)s^(-1)範圍,有10種非耐陰先驅樹種可達19.5μmol m^(-2)s^(-1)以上,以苦楝及山黃麻最高(25.7及24.0μmol m^(-2)s^(-1))。此30樹種光飽和時的氣孔導度及蒸散率分別在150~995及2~9 mmol H2Om^(-2)s^(-1)範圍。由乾季到雨季,平均光飽和光合作用率及氣孔導度分別可提高48及286%,顯示乾季時這些植株的氣孔張開程度受限很大。綜合30樹種資料,光飽和光合作用率分別與氣孔導度、蒸散率、光飽和點、光補償點及暗呼吸率有顯著正相關,但與比葉重有顯著負相關;然而應用Kendall相關性分析,發現此30樹種光飽和光合作用率的排名與上述各生理性狀的排名不具一致性。本研究也發現非耐陰種的氣體交換潛力顯著高於耐陰種,但同樣是非耐陰樹種,落葉樹種的光合作用潛力並沒有顯著高於常綠樹種。在本研究的測定條件下我們推論,台灣亞熱帶非耐陰闊葉樹種之光飽和光合作用率應在18~26μmol m^(-2)s^(-1),中等耐陰樹種可能在12~18 μmol m^(-2)s^(-1)範圍,耐陰樹種的陽葉則有5~12μmol m^(-2)s^(-1)的光飽和光合作用率。
Photosynthetic rates of 30 broadleaf tree species in Taiwan were measured in order to determine their gas exchange potential. All sampled plants were growing on sunny sites. Gas exchange variables were measured on sun-exposed leaves of each species at a leaf temperature of 28℃and CO2 concentration of 365μll^(-1) in the dry season as well as early in the rainy season. Light-saturated photosynthetic rates (A(subscript sat)) of the 30 species in the rainy season ranged from 5.5 to 25.7 μmol m^(-2)s^(-1). There were 10 shade-intolerant pioneer species whose A(subscript sat) values were higher than 19.5μmol m^(-2)s^(-1). Among them, Melia azedarach and Trema orientalis had the highest A(subscript sat) values of 25.7 and 24.0μmol m^(-2)s^(-1), respectively. Ranges of the stomatal conductance (g(subscript S)) and transpiration rate (E) at the light saturation point (LSP) of the 30 species were 150~990 and 2~9μmol m^(-2)s^(-1), respectively. Mean A(subscript sat) and g(subscript S) values measured in the rainy season increased 48 and 286%, respectively, compared to those measured in the dry season, indicating that stomatal openness of these plants was severely restricted during the dry season. Combining data from measurements of the 30 species, A(subscript sat) was positively correlated to g(subscript S), E, the LSP, light compensation point (LCP), and dark respiration (Rd), but was negatively correlated to the leaf mass per area. However, the ranking of A(subscript sat) values of the 30 species was not consistent with the rankings of g, E, LSP, LCP, or Rd when Kendall’s tau coefficient was applied. Results of this study confirmed that shade-intolerant species have higher gas exchange potentials than shade-tolerant species. However, there were no significant differences in A(subscript sat) values between deciduous and evergreen shade-intolerant species. We propose that for sun leaves of subtropical broadleaf trees in Taiwan, shade- intolerant pioneer species may have A(subscript sat) values of between 18 and 26μmol m^(-2)s^(-1). shade-tolerant pecies of between 5 and 12μmol m^(-2)s^(-1), and intermediate species of between 12 and 18μmol m^(-2)s^(-1).
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