藏东南色季拉山薄毛海绵杜鹃叶解剖结构特征与环境适应性

以藏东南色季拉山9个不同海拔梯度的薄毛海绵杜鹃(Rhododendron aganniphum var.schizopeplum)叶片为试验材料,采用石蜡切片技术,测定10项叶片解剖结构指标,应用叶片解剖结构指标的可塑性指数和相关性分析方法探索薄毛海绵杜鹃对藏东南色季拉山强紫外辐射和高寒环境的适应性。结果表明:(1)薄毛海绵杜鹃叶片为异面叶,上表皮有明显的角质层,下表皮有表皮毛,栅栏组织细胞2～3层。(2)随着海拔的升高,叶片角质层厚度、上下表皮厚度、栅栏组织厚度、海绵组织厚度、叶片厚度呈现明显增大趋势,而组织结构紧密度和疏松度变化不显著,主脉突起度呈现下降趋势。(3)各项叶片解剖结构指标的可塑性指数显示,薄毛海绵杜鹃在解剖结构上表现出较小的可塑性,对外界环境的适应能力较弱。(4)依据薄毛海绵杜鹃各项叶片解剖结构指标的相关性分析结果,除海绵组织厚度与栅栏组织厚度、下表皮厚度与上角质层厚度之间相关性不显著外,其余各指标之间均呈显著相关关系,且叶片的解剖结构指标方面也存在明显的协同进化现象。研究发现,藏东南色季拉山薄毛海绵杜鹃通过增加叶片角质层厚度、表皮厚度和叶肉厚度等解剖结构指标的方式增强对外界极端环境的适应能力,从而有利于其在恶劣的高山生境下生存繁衍,使该物种成为生态位理论中的广幅种。

Anatomical Characteristics and Environmental Adaptability of Rhododendron aganniphum var. schizopeplum Leaf in Sejila Mountain, Southeastern Tibet

In order to understand the adaptability of Rhododendron aganniphum var. schizopeplum to strong ultraviolet radiation and alpine environment, we studied the anatomical structures of leaves from nine altitude gradients in Sejila Mountain, Southeastern Tibet by the method of paraffin section. Ten anatomical structure indexes of leaves were measured and analyzed by plasticity index and correlation coefficient. The results showed that: (1) the leaves of R. aganniphum var. schizopeplum were bifacial, the upper epidermis had obvious cuticle, the lower epidermis had trichomes, and the palisade tissue cells had 2-3 layers. (2) As the altitude became higher, the thickness of cuticle, epidermis, palisade tissue, sponge tissue and leaf increased obviously. However, the density and porosity of the tissue structure did not change significantly, and the protuberance of the main vein decreased. (3) The plasticity index showed R. aganniphum var. schizopeplum had lower plasticity, which represented weak adaptability to environment. (4) The indexes were significantly correlated with each other and presented obvious coevolution, except that there were no significant correlations between the thickness of sponge tissue and palisade tissue, between the thickness of lower epidermis and upper cuticle. In summary, R. aganniphum var. schizopeplum adapts to the extreme environment, survives in harsh alpine habitats and becomes a eurytopic species by means of increasing the thickness of cuticle, epidermis, mesophyll and anatomical structure indexes.