Physiological Drought Tolerance of Tree Species Inhabiting the Ridge of the Kenting Karst Forest

墾丁喀斯特森林礁頂樹種的生理耐旱性

郭耀綸(Yau-Lun Kuo) ； 蔡國鐘(Kuo-Chung Tsai)

《台灣林業科學》 33卷3期 (2018/09) Pp. 213-230

https://doi.org/10.7075/TJFS.201809_33(3).0004

摘要

The topography and tree species compositions significantly differ between the ridge and valley habitats of the Kenting karst forest, southern Taiwan. The objective of this research was to explore how tree species inhabiting the ridge habitat have adapted to the drought environment in terms of physiological traits and leaf morphology. Drypetes littoralis and Aglaia formosana, 2 species inhabiting the ridge, were investigated for this purpose. As a comparison, Pisonia umbellifera and Melanolepis multiglandulosa, 2 species inhabiting the valley, as well as Diospyros maritima which is distributed in both habitats, were also studied. Results showed that ridge species had a significantly higher leaf mass per area than did valley species. The predawn leaf water potential (PWP) during the dry season was significantly lower than that during the rainy season for each of the 5 species. The net photosynthetic rate (P_n) during the dry season was also significantly lower than that during the rainy season for 4 species, with the exception of P. umbellifera. During the dry season, the PWP of ridge species Dry. littoralis and A. formosana decreased to -3.40 and -3.69 MPa, respectively, indicating that these 2 species were suffering severe water stress, while the valley species were experiencing only mild water stress. Yet, these 2 ridge species still maintained positive P_n values at about 46 and 25%, respectively, of the P_n during the rainy season. Individuals of Dio. maritima growing in the ridge habitat showed a slightly lower PWP than that of the same species growing in the valley habitat (-1.88 vs. -1.29 MPa) during the dry season, but maintained the P_n at 62% of the P_n during the rainy season. To have their P_n values decline to 0, the PWPs of ridge species Dry. littoralis, A. formosana, and Dio. maritima would need to be as low as -5.89, -4.84, and -5.03 MPa, respectively. The results indicated that these 3 ridge species possessed a high physiological tolerance ability and could adapt to the stressful conditions of strong winds and water deficits in the ridge habitat during the dry season. Individuals of Dio. maritima growing in the ridge habitat showed both physiological and morphological acclimation to the drought environment.

關鍵字

drought environment ； karst forest ； net photosynthetic rate ； physiological drought tolerance ； predawn leaf water potential

並列摘要

墾丁喀斯特森林礁頂及峽谷兩生育地，在地形及樹種組成上有明顯差異。本研究探討長在礁頂的樹種，生理性狀及葉形態如何適應乾燥環境。供試樹種為長在礁頂的鐵色及紅柴，並以長在峽谷的皮孫木及蟲屎，以及兩處均有的黃心柿做比較。結果發現礁頂樹種的比葉重顯著高於峽谷的樹種。供試5樹種乾季的黎明前葉部水勢都顯著低於雨季。除了皮孫木，另4樹種乾季的淨光合作用率也都顯著低於雨季。乾季時鐵色及紅柴的黎明前葉部水勢分別低至-3.40及-3.69 MPa，顯示遭嚴重水逆境，而峽谷樹種僅遭輕微水逆境。乾季時鐵色及紅柴淨光合作用率均仍為正值，分別可維持雨季時的46及25%。長在礁頂的黃心柿，黎明前水勢僅稍低於峽谷的同種植株（-1.88 vs. -1.29 MPa），淨光合作用率則可維持雨季時的62%。礁頂的鐵色、紅柴及黃心柿，黎明前水勢分別要低至-5.89, -4.84, -5.03 MPa時，淨光合作用率才會降至零。結果顯示此三樹種生理耐旱性強，能適應礁頂生育地乾季時強風且缺水的逆境。此外，礁頂黃心柿植株的生理活動及葉形態兩方面都有馴化乾燥環境的表現。

並列關鍵字

乾燥環境 ； 喀斯特森林 ； 淨光合作用率 ； 生理耐旱性 ； 黎明前葉部水勢