藏麻黄与丽江麻黄的形态及遗传变异研究

麻黄属(Ephedra)起源较早，该属植物的形态性状极度退化或简化，可用于经典分类学的有价值的性状非常有限。分布于青藏高原的藏麻黄（E. saxatilis）和丽江麻黄（E. likiangensis）二者间形态相似，性状变异连续，很难分辨，但被《中国植物志》中、英文版作两个种处理。 本文对藏麻黄和丽江麻黄的七个居群、151个个体的叶、雌球花和节间长等形态学性状进行了分析，发现各性状的变异情况在群体间无明显差异。同时我们还对154个个体的叶绿体DNA trnT-trnF和 trnS-trnfM区进行了序列分析，两个片段的联合矩阵长1382bp，共有29个变异位点，其中有9个碱基变异和2个indel，可划分为H1、H2和H3三种单倍型。这3种单倍型在丽江麻黄中均有分布，但藏麻黄仅含H1和H2。 综合来自形态学和分子方面的证据，我们发现藏麻黄和丽江麻黄的关系非常近缘，因此建议予以合并。同时本文还以膜果麻黄（E. przewalskii）为外类群，从谱系生物地理学角度探讨了三种叶绿体单倍型的进化关系，发现H2最原始，分布最广;H1与其它两种单倍型间的序列差异较大，可能是较进化的类型。此外，无性克隆的繁殖方式可能是导致Ephedra单倍型非常简单的重要原因之一。

Phylogeography of Pinus tabulaeformis Carr. (Pinaceae), a dominant species of coniferous forest in northern China

How coniferous trees in northern China changed their distribution ranges in response to Quaternary climatic oscillations remains largely unknown. Here we report a study of the phylogeography of Pinus tabulaeformis, an endemic and dominant species of coniferous forest in northern China. We examined sequence variation of maternally inherited, seed-dispersed mitochondrial DNA (mtDNA) (nad5 intron 1 and nad4/3-4) and paternally inherited, pollen- and seed-dispersed chloroplast DNA (cpDNA) (rpl16 and trnS-trnG) within and among 30 natural populations across the entire range of the species. Six mitotypes and five chlorotypes were recovered among 291 trees surveyed. Population divergence was high for mtDNA variation (G(ST) = 0.738, N-ST = 0.771) indicating low levels of seed-based gene flow and significant phylogeographical structure (N-ST > G(ST), P < 0.05). The spatial distribution of mitotypes suggests that five distinct population groups exist in the species: one in the west comprising seven populations, a second with a north-central distribution comprising 15 populations, a third with a southern and easterly distribution comprising five populations, a fourth comprising one central and one western population, and a fifth comprising a single population located in the north-central part of the species' range. Each group apart from the fourth group is characterized by a distinct mitotype, with other mitotypes, if present, occurring at low frequency. It is suggested, therefore, that most members of each group apart from Group 4 are derived from ancestors that occupied different isolated refugia in a previous period of range fragmentation of the species, possibly at the time of the Last Glacial Maximum. Possible locations for these refugia are suggested. A comparison of mitotype diversity between northern and southern subgroups within the north-central group of populations (Group 2) showed much greater uniformity in the northern part of the range both within and between populations. This could indicate a northward migration of the species from a southern refugium in this region during the postglacial period, although alternative explanations cannot be ruled out. Two chlorotypes were distributed across the geographical range of the species, resulting in lower levels of among-population chlorotype variation. The geographical pattern of variation for all five chlorotypes provided some indication of the species surviving past glaciations in more than one refugium, although differentiation was much less marked, presumably due to the greater dispersal of cpDNA via pollen.