我国北方岩溶泉域刚毛藻的系统发育及形态学研究

脆弱刚毛藻(Cladophora fracta)是一种大型丝状绿藻,生境分布广泛。然而,对于岩溶泉域分布的刚毛藻研究较少,它们的遗传多样性、生物地理亲缘性和生理特性都有待于深入研究。该研究对我国北方地区五个典型岩溶泉域的50个脆弱刚毛藻样本进行了形态学和分子系统学描述。主要研究目标:(1)对我国北方地区五个典型岩溶泉的刚毛藻生境进行描述;(2)根据形态学特征和分子序列对藻体进行鉴定;(3)探究生境对藻体生理特性的影响。结果表明:基于SSU和LSU序列的结果,发现所分析的50株刚毛藻个体为同一种,同时还发现了13个不同的核糖体基因型。基于SSU和LSU的系统发育树,刚毛藻属均未能形成单系分支,分布在三个不同的分支上。13个样本基因型在SSU和LSU树中的位置相似,与Cladophora vagabunda有很高的序列同源性,但是形态特征却差异很大。从显微结构结果来看,五个岩溶泉域采集到的刚毛藻在细胞直径上无显著差异,藻体的形态特征与脆弱刚毛藻相一致。但是,岩溶泉域采集的藻体细胞直径比文献报道中在湖泊和河流中采集的脆弱刚毛藻直径要大。另外,仅在两个地点(XA和ST)采集的标本中发现有假根状分枝。因此,基于形态学和分子序列的结果,将这五个泉域的刚毛藻鉴定为脆弱刚毛藻(Cladophora fracta)。

Phylogenetic and morphological profile of Cladophora fracta (Cladophorophyceae, Chlorophyta)from karst springs, in North China

Cladophora fracta, a filamentous green macroalgal epiphyte on rhodoliths, is described from five karst springs in North China. Although Cladophora species frequently appear in karst system, their genetic diversities, biogeographical affinities and physiological properties have not been well investigated in these environments. The specific objectives of this study were as follows:(1)Describe the habitat of the cladophora-like algae form the five karst springs;(2)Identify the thallus to species level based on a combination of morphological characteristics and molecular sequence;(3)Explore the morphological influence of habitat. To elucidate the biogeographical patterns in Cladophora, both morphological and molecular evidence were compared of Cladophora specimens across five study sites. Analyses of partial small subunit(SSU)and large subunit(LSU)genes revealed that the studied 50 Cladophora specimens were genetically identical species and a total of thirteen ribotypes were detected. The molecular sequencing results indicated that the examined species was highly homologous with C. vagabunda, though they shared few morphological features. The genus did not form a monophyletic clade but in three different clades both in SSU and LSU trees. The microscopic structure was more consistent with that of C. fracta. The Cladophora from the five karst springs did not show significant variation in cell dimensions. However, the species exhibited larger cell diameters than those reported from lakes. In addition, the rhizoid-like branches are only observed in two locations(XA and ST). Considering the morphological characteristics, we therefore hold our species as C. fracta.