摘要
白背芒 ( Miscanthus sinensis var. glaber (Nakai) J. Lee ) 分布在台灣中低海拔1200公尺以下的山區，屬於先驅性、演替早期的風媒物種。
本研究分別在台灣北、中、南三個地區採集十個族群382株白背芒，利用澱粉凝膠電泳法探討白背芒的族群遺傳結構，並在台灣東北部採集二個亞族群70株白背芒進行微棲地天擇效應的檢測。總共分析了九種酵素，十五個基因座，得到結果如下：( 1 ) 白背芒全體族群的異合度期望值 ( HE ) 平均為0.146，族群間的遺傳歧異度 ( GST ) 為0.147，都接近以風力傳播種子之物種的平均值，且其族群間有高度分化的情形 ( FST = 0.158 )。( 2 ) 根據基因流傳值 ( Nm = 1.33 ) 與特有基因的出現判斷，白背芒全體族群的基因交流受到阻礙。( 3 ) 在同一棲地的族群內，不同微環境的亞族群間有中度分化的現象 ( FST = 0.077 ) 證明了地區性的天擇力量對於白背芒族群遺傳結構的影響力。( 4 ) 北大武山為一封閉隔離的地區，且其白背芒族群與其他族群間的遺傳相似度低於Gottlieb ( 0.95 ) 及Thrope ( 0.96 ) 提出的種內族群平均遺傳相似度，故經由以上結果判斷，北大武山的白背芒可能是由地區性天擇作用下建立起來的隔離族群。

ABSTRACT
The perennial herbaceous Miscanthus sinensis var. glaber (Nakai) J. Lee is a pioneer and early successional status species that can be found in altitude less than 1200 m.
A total number of 382 samples of M. sinensis var. glaber from ten localities ranging from Northern, Central and Southern Taiwan were collected to determine their population genetic structure. In addition, 70 samples representing two subpopulations in Northeastern Taiwan were collected for studying the nature selection of microhabitats. Fifteen loci from nine isozymes by Biosys-II were obtained and the results showed that the mean expected value of the heterozygosity ( HE ) is 0.1459 and the proportion of the total diversity among populations ( GST ) is 0.147, that correlated with those of species which disperse seeds by wind. The gene flow rate ( Nm = 1.33 ) and the acquisition of private gene suggest that the gene flow of Miscanthus sinensis var. glaber is retarded. The middle genetic differentiation ( FST = 0.077 ) among the subpopulations in different microhabitate showed the major force that acts on the population genetic structure of M. sinensis var. glaber is local sellection. The mean population genetic similarity ( 0.91 ) between samples from the geographically isolated area, Pei-Ta-Wu Mountain, and those from othe populations collected from rest nine sites is lower than that proposed by Gottlieb ( 0.95 ) and Thrope ( 0.96 ). The results indicated that the population in Pei-Ta-Wu Mountain might have been confined by local selection.

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