藉由光合作用性狀判斷30種臺灣原生闊葉樹種的耐陰性

本研究測定栽植於屏東科技大學森林系苗圃30種臺灣原生闊葉樹種之光合潛力。測定時將CO2濃度控制在400 μl L-1，葉溫28℃，相對溼度70~80%。將各樹種的光合潛力量化數據當作該樹種耐陰性的生理指標，成果可增加臺灣原生樹種耐陰性的資料庫名錄。結果發現，此30樹種的光合潛力範圍在7.8~27.6 μmol CO2 m-2 s-1之間；光飽和點在742~1569 µmol photon m-2s-1；光補償點分布8.8~27.1 µmol photon m-2s-1之間；暗呼吸率範圍在0.85~2.33 µmol CO2 m-2s-1。光合潛力最高的樹種為厚殼樹，最低者為交力坪鐵色。將此30種林木對應五項耐陰性級別，結果先驅樹種只有厚殼樹；陽性樹種有5種，包括沙朴、小葉桑、亞洲濱棗、蓪草及菲律賓饅頭果；中等耐陰樹種也有5種，包括菲律賓榕、倒卵葉蕘花、天料木、臺灣香檬及火燒栲；耐陰樹種有14種，包括粗糠柴、印度苦櫧、樟葉槭、多花山柑、菲律賓楠、短尾葉石櫟、森氏櫟、高山櫟、浸水營石櫟、秀柱花、天臺烏藥、石楠、山柚仔及對面花；極耐陰樹種有5種，包括尖葉水絲梨、山柑、呂宋毛蕊木、小花鼠刺及交力坪鐵色。供試30種樹種的光合潛力與光補償點或暗呼吸率間皆呈顯著正相關，顯示以光補償點或暗呼吸率此兩參數判斷林木耐陰性具可行性。本研究也測定不同耐陰樹種溫度由20℃逐步提高至30℃，對光補償點及暗呼吸率的影響。結果發現，溫度上升會提高供試樹種的光補償點及暗呼吸率。分別屬於先驅樹種與陽性樹種之臺灣山麻桿及菲律賓饅頭果的光補償點對溫度提高的反應較敏感，而極耐陰樹種交力坪鐵色的暗呼吸率對溫度上升的變化相對較不敏感。本研究新增臺灣原生闊葉樹種30種的耐陰性名錄，可供育林、園林植栽、樹種空間配置，以及林下經濟應用之參考。

關鍵字

光合潛力；光補償點；暗呼吸率；耐陰性名錄

並列摘要

This research measured the photosynthetic capacity of 30 native broadleaf tree species of Taiwan. These trees were cultivated in the nursery of Department of Forestry, National Pingtung University of Science and Technology. When taking the measurements, CO2 concentration was set at 400 μl L-1, leaf temperature at 28℃, and relative humidity at 70~80%. Using quantified photosynthetic capacity as a physiological indicator of shade tolerance ability of each species, the result can expend the species list of shade tolerance data base of Taiwan. The photosynthetic capacity of the 30 species was within the range of 7.8~27.6 μmol CO2 m-2 s-1, light saturation point within 742~1569 µmol photon m-2s-1, light compensation point within 8.8~27.1 µmol photon m-2s-1, and dark respiration rate within 0.85~2.33 µmol CO2 m-2s-1. Ehretia acuminata had the highest photosynthetic capacity, while Drypetes karapinensis the lowest. Categorizing the 30 species into the 5 corresponding shade tolerance levels, results showed that only E. acuminata fit into pioneer species category. There were 5 shade intolerant species, including Celtis sinensis, Morus australis, Colubrina asiatica, Tetrapanax papyriferus, and Glochidion philippicum. There were also 5 mid-tolerant species, including Ficus ampelas, Wikstroemia retusa, Homalium cochinchinensis, Citrus depressa, and Castanopsis fargesii. There were 14 shade tolerant species, including Mallotus philippensis, Castanopsis indica, Acer albopurpurascens, Capparis floribunda, Machilus philippinensis, Pasania harlandii, Cyclobalanopsis morii, Quercus spinosa, Pasania shinsuiensis, Eustigma oblongifolium, Lindera aggregata, Photinia serratifolia, Photinia serratifolia, and Randia spinosa. There were 5 very shade tolerant species, including Distyliopsis dunnii, Capparis sikkimensis, Gomphandra luzoniensis, Itea parviflora, and D. karapinensis. The photosynthetic capacity of all the 30 tested species showed significantly positive relationships with either light compensation point or dark respiration rate, indicating the feasibility of adopting light compensation point or dark respiration rate to determine the shade tolerant ability of a species. This study also measured the influence of gradually increased temperature from 20℃ to 30℃ to the light compensation point and dark respiration rate of different shade tolerance species. Results showed that increased temperatures would raise the light compensation point and dark respiration rate of a species. The light compensation point of Alchornea trewioides and G. philippicum, which belong to the pioneer species and shade intolerant species, showed a very sensitive response to increased temperatures, while the dark respiration rate of D. karapinensis, a very shade tolerant species, showed less sensitive response to increased temperatures. This study added 30 native broadleaf tree species of Taiwan to the shade tolerance list, providing references for the applications in silviculture, arboriculture, spatial allocation, and under-canopy economics.