| 摘要: | 台灣高山杜鵑為台灣高山原生杜鵑之一，根據文獻檢索發現目前針對台灣高山杜鵑族群遺傳結構分析之研究甚少，也缺乏探討其與氣候變遷之相關性。因此本研究欲利用微衛星（microsatellite）DNA基因座之高變異性的特性探討台灣高山杜鵑在合歡山三個樣區的族群遺傳結構是否受到氣候變遷的影響。在本研究發現因為異型合子的減少導致基因多型性的減少，結果顯示分離出之8組基因座皆偏離哈溫定律，分化指數平均值為0.0532，屬於低等分化。從遺傳歧異度與族群數大小的結果分析可以發現分佈於較高海拔之族群數較小，其歧異度低，脆弱度增加。推測台灣高山杜鵑遺傳歧異度與分布之海拔高度有關，亦即台灣高山杜鵑的脆弱度與氣溫有相關。
在合歡山東?步道的研究樣區可以發現大片玉山杜鵑叢生，且植被下植物種類少，可謂當地之優勢物種。因此本研究欲探討玉山杜鵑之相生相剋作用，結果顯示濃度1 % ~ 5 %之玉山杜鵑葉片水萃取液對萵苣、小白菜、大花咸豐草及莧菜之種子發芽及幼根生長有抑制作用。此外，植物殘體在分解過程中也會釋出相剋物質以抑制鄰近植物的生長，因此本研究欲探討玉山杜鵑葉片在經由水的分解過程中，會釋放出何種相剋物質，以及在水的分解過程中其相生相剋能力是否會受到分解時間長短的影響。將玉山杜鵑葉片50 g浸泡在950 ml蒸餾水中於室溫下讓其分別分解1、2、4及8週並得其水萃取液，以上述植物種子做生物分析，結果顯示玉山杜鵑葉片之水萃取液不論是否有經過分解處理，對試驗種子發芽之幼根根長生長皆有抑制效果；觀察其毒性動態變化可以發現在第一次及第二次萃取之水萃取液抑制效果最大，第三次萃取之後抑制效果漸漸減低。對其水萃取液進行紙色層分析，發現含有酚酸類物質，如o-hydroxyphenylacetic、vanillic acid、p-coumaric acid、syringic acid、p-hydroxybenzoic acid、3,4,5-trimethoxybenzoic acid、veratric acid、gentisic acid、protocatechuic acid、ferulic acid、o-coumaric acid、caffeic acid。玉山杜鵑在東?可以視為優勢植物，除了已適應當地氣候、地理環境之外，其葉部含有植物相剋物質可以抑制其他植物物種的生長，導致杜鵑林下之植被物種減少。
Rhododendron rubropilosum Hayata var. taiwanalpinum, one of the endemic Rhododendron species, distributes in high mountain area of Taiwan. According to the literature review, little information on genetic structure and its relationship with climate changes was reported. In this study, the genetic structure of R. rubropilosum taiwanalpinum in relation to climate changes was examined based on microsatellite loci. The result indicated that the isolated eight microsatellite loci were significantly deviated from Hardy–Weinberg expectations due to the heterozygote deficiency which showed the loss of genetic polymorphisms. The FST of R. rubropilosum taiwanalpinum was 0.0532 on average, showing lower differentiation. The analysis of the relationship between genetic diversity and population size revealed that the vulnerability of population was correlated to the population size and low diversity in the higher altitude of this area. The findings suggested that the genetic diversity of R. rubropilosum taiwanalpinum was positively correlated to population size as affected by temperature, and also correlated to the altitude of its distribution.
Rhododendron pseudochrysanthum Hayata, a dominant vegetation, is almost lacking of understory species along the trail of East Peak of Mt. Hohuan. Based on our observation, we thus hypothesized that the unique phenomenon might be due to the allelopathy. To test the hypothesis, bioassays of the 1% to 5% aqueous extracts of leaves of R. pseudochrysanthum showed significant inhibition on radicle growth of Brassica chinensis, Lactuca sativa, Amaranthus gangeticus and Bidens pilosa. Because plant residues of the Rhododendron may release allelopathic compounds to suppress the growth of understory species during the decomposing plant residues in soil, we thus conducted a serious of experiment by using 50 g leaves soaked in 950 ml distilled water and allowed the leaves to be decomposed in different time intervals, 1, 2, 4, 8 weeks. The aqueous extracts were obtained at the elapsed intervals of decomposition, and were bioassayed. The bioassay results of the aqueous extracts showed significant inhibition on radicle growth of B. chinensis, L. sativa, A. gangeticus and B. pilosa. We also found the most inhibition was shown in the first and second aqueous extracts, but the phytotoxicity decreased in the subsequent extracts. Furthermore, phytotoxic phenolic acids, such as o-hydroxyphenylacetic, vanillic acid, p-coumaric acid, syringic acid, p-hydroxybenzoic acid, 3,4,5-trimethoxybenzoic acid, veratric acid, gentisic acid, protocatechuic acid, ferulic acid, o-coumaric acid and caffeic acid were tentatively identified as compared with authentic compounds by means of paper chromatography. The amount of these compounds was decreasing with time interval of decomposition, indicating that the phytotoxicity decrease was correlated to the amount of phytotoxic phenolics present in the extracts. Regardless of the adaptation of Rhododendron plants to the climate and environment, the existence of allelochemicals might be responsible for the exclusion of plant species underneath Rhododendron stands, resulting in the low plant diversity of understory species. |
