ABSTRACT

Though variability in morphological features along the environmental gradients has been extensively studied, less information is available on possible adaptations and trends of anatomical features. We examined the variation in morphological and stem anatomical features of a widely distributed (2,200–5,300 m a.s.l.) Rhododendron lepidotum across elevation gradients in Langtang and Sagarmatha National Parks of Nepal Himalayas. Plant samples in each site were collected from three elevation bands (ca. 3,000, 4,000, and 5,000 m a.s.l.). In both study sites, all morphological features measured had their highest value at the lowest elevation and vice versa. Vessel density of basal stem increased but diameter and area of xylem vessels, and length of vessel element and fiber tracheids decreased as elevation increased. Similarly, height and the number of cells in uniseriate rays and height, width, area, and density of multiseriate rays also decreased toward the highest elevation. However, anatomical features of the ultimate branch did not show any distinct pattern with elevation. Morphological features showed more plasticity than anatomical features along the elevation gradients. Decreased plant height, individual leaf area, specific leaf area, and the existing trade-off relationship between vessel diameter and density could have supported a wide distribution of R. lepidotum in Nepal Himalayas.

摘要

尽管已经广泛研究了沿环境梯度的形态特征的变异性，但是关于解剖特征可能的适应性和趋势的信息很少。我们研究了分布广泛的（2,200-5,300 m asl）杜鹃花鳞状细胞的形态和茎部解剖特征的变化尼泊尔喜马拉雅山的郎塘和萨加玛塔国家公园的海拔梯度变化。从三个海拔带（大约3,000、4,000和5,000 m asl）收集每个站点的植物样本。在两个研究地点，所有测得的形态学特征在最低海拔处均具有最高值，反之亦然。基底茎的血管密度增加，但木质部血管的直径和面积随高度的增加而减小，而血管元件和纤维气管的长度则减小。同样，单边射线的高度和细胞数以及多边射线的高度，宽度，面积和密度也朝最高海拔方向降低。但是，最终分支的解剖特征并未显示出任何明显的抬高图案。沿海拔梯度，形态特征比解剖特征显示出更多的可塑性。R. lepidotum在尼泊尔喜马拉雅山。