雪山雪東線步道玉山杜鵑葉片結構特徵沿海拔梯度的變化

Variation of leaf traits of Rhododendron pseudochrysanthum along an altitudinal gradient at the East Xue Trail of the Xue Mountain

葉片結構特徵具相對穩定性，能反應植物對環境的適應對策。本研究以雪山雪東線步道沿線的玉山杜鵑為材料，以葉面積和葉解剖構造等性狀探討葉結構特徵沿海拔梯度的變化趨勢，同時比較玉山杜鵑營養枝與繁殖枝的葉結構特徵差異，以及探討玉山杜鵑種複合群葉結構特徵的分化。結果顯示玉山杜鵑葉片各性狀沿雪山雪東線海拔梯度呈顯著差異。葉面積、比葉面積與葉乾重明顯隨海拔上升而遞減；葉片厚度、柵狀組織厚度、柵狀組織細胞長度、柵狀組織層數、海綿組織厚度、上表皮厚度，以及上表皮細胞層數、氣孔密度等則大致沿海拔升高呈遞增的趨勢。玉山杜鵑葉結構特徵隨海拔的變化，反應在對環境適應上的表現，其中葉面積變小，葉厚度、上表皮、柵狀與海綿組織的增厚，以及氣孔密度增加等性狀之改變，皆有助於對高山低溫、強輻射、乾旱以及較低CO2濃度的適應。營養枝與繁殖枝的葉片性狀在柵狀組織厚度、葉上表皮厚度、柵狀組織與葉片厚度比、氣孔長度等性狀呈顯著差異。研究區玉山杜鵑的葉結構特徵約可分成3群，與海拔和生育地環境（位於林內或開闊地）有關，大致反映其與種複合群－森氏杜鵑之關係，反映出玉山杜鵑在雪東線步道沿線分布環境的岐異性。玉山杜鵑種複合群的葉片性狀研究有待蒐集更多樣本，例如南湖杜鵑與紅星杜鵑等進行分析及探討。

Leaf structural traits are relative stable, it often reflect the strategies of plants adapting to the environment. In this study, we analyzed the variation of leaf structure traits of Rhododendron pseudochrysanthum Hayata along an altitudinal gradient on the East Xue Trail of Xue Mountain, and compared the differences of the leaf characteristics between reproductive- and vegetative-branch, as well as the differentiation of the leaf structure among different species-complex group. The results showed significant differences in leaf traits of R. pseudochrysanthum along the altitude gradient. Leaf area, dry weight and specific leaf area significantly decreased with increasing altitude; whereas, the thickness of leaf, palisade tissue, sponge tissue, epidermis, layers of palisade tissue and upper epidermal cell, palisade tissue cell length, and stomatal density generally increased along the elevation of the altitude. These differences correlated with the elevation suggested that the leaf traits in R. pseudochrysanthum changed to adapt to the environment. Among the changes of the leaf traits, decreased leaf area, increased leaf thickness, epidermis, palisade and spongy tissue, and stomatal density benefit the adaptation to harsh environment such as strong radiation, drought and low CO2 concentration in the higher elevation. Stomata length, thicknesses of palisade tissue and leaf epidermis, thickness ratio between palisade tissue and leaf showed significant differences between reproductive- and vegetative-branch, whereas the difference of leaf area and specific leaf area were not significant. The leaf structural traits of R. pseudochrysanthum can be broadly divided into three groups, indicated that leaf traits could change with the altitude and habitats (under forest and open place), reflecting the environmental diversity of R. pseudochrysanthum and one of its species complexes- R. morii Hayata distributed along the East Xue Trail. Further studies of leaf traits in R. nankotaisanense Hayata and R. hyperythrum Hayata that form species complex with R. pseudochrysanthum are necessary.