喀斯特地区莎叶兰的解剖构造及其环境适应性

以广西西北部雅长兰科植物保护区的莎叶兰( Cymbidium cyperifolium)为对象,采用石蜡切片法对莎叶兰叶片和根的解剖构造及其对喀斯特环境的适应性进行了研究。结果表明：(1)莎叶兰叶片的上表皮覆盖有较厚的角质层,气孔均分布于下表皮,且凸出表皮细胞之上；各表皮性状在叶片不同部位存在显著差异,叶片下部的气孔密度、气孔指数和气孔长度最大,表皮细胞密度以叶片上部的最大；叶片属于等面叶,叶肉无栅栏组织和海绵组织的分化；叶脉为明显的平行脉,且粗细交互分布；(2)莎叶兰根的横切面包括根被、皮层、中柱3部分,其中根被细胞排列紧密,为生活细胞；皮层由薄壁细胞组成；根部维管束属于辐射维管束,14原型。菌根粗壮,稀根毛,共生真菌主要分布于根被及皮层中,菌丝体通过根被薄壁细胞间隙及内、外皮层的通道细胞进行侵染。(3)莎叶兰叶片和根的结构不仅有湿生植物特征,如叶片相对较薄、气孔少且凸出表皮细胞、冠/根比值大等；还有旱生植物的特征,如叶片角质层较厚、机械组织发达、细胞结构紧密、具含晶细胞,肉质根具根被,内、外皮层细胞壁明显增厚等。这些结构是莎叶兰对当地缺水、干湿季明显、分布于林下多石砾土壤的生长环境的一种高度适应性表现。

Anatomical structure and environmental adaptability of Cymbidium cyperifolium in karst area

The leaf and root anatomical structures of Cymbidium cyperifolium in Yachang Orchids Nature Reserve of Northwest Guangxi were studied by using traditional paraffin section, and its adaptability to karst environment was also analyzed. The results were as follows:(1)The upper epidermal cells of C. cyperifolium were covered with thick cuticle. The stomata were distributed in lower epidermal cells and protruding on epidermal cells. All epidermal trait features had significance difference among different parts of leaf blade. The highest stoma density, stoma index and length of stoma were in the lower part of leaf blade, and maximum density of epidermal cells was in the upper part of leaf blade. The leaves of C. cyperifolium were equifacial leaf and the mesophyll was not differentiated into palisade and spongy tissues. The leaf vein was distinct parallel venation. Thick and thin veins were interactively distributed.(2)The root cross section was composed of root velamen, cortex and stelae. Root velamen cells lived and arranged closely. Cortex was composed by parenchyma cells. Root vascular bundle belonged to radial vascular bundle. The mycorrhiza was thick and had few root hairs. The symbiotic fungi mainly distributed in root velamen and cortex, and infection of mycelium was invaded through the parenchyma intercellular space and the passage cells of cortex by hyphae.(3)The leaf and root anatomical structures of C. cyperifolium not only had hygrophyte features, such as relatively thinner leaf blade, less and protruding stoma and higher ratio of shoot mass to root mass, but also had xerophytes features, such as thicker cuticle, developed mechanical tissue, tensely cell structure, having crystal cell, fleshy root had velamen, obviously thickening cell wall of inner and outer cortex. These structures of C. cyperifolium represent the adaptability to living environment with water deficit, obvious dry and wet seasons and understory gravel soil.