西藏东达山3种嵩草属植物气孔特征沿海拔的变化

嵩草属(Kobresia)植物是藏东南高山草甸的优势种和建群种,对该区畜牧业发展和维持生态系统平衡起着重要作用。选择西藏左贡县东达山为研究地点,从林线开始,海拔每升高约100m设置1个样带直至高山草甸分布边缘,共8个样带,调查各样带中物种的组成及盖度,并依据相对盖度和相对频度计算3种嵩草植物矮生嵩草(K.humilis)、线叶嵩草(K.capillifolia)和大花嵩草(K.macrantha)在群落中的重要值,同时取样观察它们叶片远、近轴面表皮细胞形态,测量气孔长度及保卫细胞宽度,计算气孔密度,探讨嵩草属植物对海拔梯度的适应性。结果表明:(1)3种嵩草属植物叶表皮细胞均呈波浪状,气孔器仅分布于远轴面,近轴面无气孔器分布。(2)3种嵩草属植物气孔密度沿海拔梯度的变化均呈单峰曲线分布格局,且在海拔4 537m样带处达到最大值,并表现为矮生嵩草(777.6个/mm2)线叶嵩草(476.4个/mm2)大花嵩草(414.3个/mm2)。(3)随海拔的增加,矮生嵩草和线叶嵩草气孔长度显著增大(P0.05),而保卫细胞宽度显著减小;但大花嵩草气孔长度随海拔的升高而显著减小,保卫细胞宽度基本保持不变。(4)矮生嵩草和线叶嵩草气孔密度、长度和保卫细胞宽度与海拔梯度均显著相关,气孔特征对海拔梯度变化的敏感程度高,与其在群落中重要值高的分布特征一致;而大花嵩草仅气孔密度和长度与海拔梯度显著相关,气孔特征对海拔梯度变化的敏感性低,与其在群落中重要值低的分布特征一致;嵩草属植物气孔密度、长度和保护细胞宽度与海拔梯度之间的相关性,反映出它们在海拔梯度上对生境的适应程度。可见,3种嵩草属植物气孔特征对海拔梯度上生境变化的适应性不同,从而影响它们在群落中的分布范围和物种优势度,其中矮生嵩草和线叶嵩草对环境变化敏感,而大花嵩草对环境变化相对不敏感;保卫细胞宽度与气孔长度同样对植物适应环境变化起重要作用。

Variations of Stomatal Characters for Three Species of Genus Kobresia along an Elevational Gradient in the Dongda Mountains of Tibet

Species of genus Kobresia are the dominants and edificators in southeast Tibet alpine meadow, and play important roles in the livestock production and stabiligy of ecosystem. To study the adaptation of different characteristics of Kobresia plant to elevational gradient, we set eight sample belts along an elevational gradient, starting from forest line to the edge of alpine meadows, as increasing of elevation for every about 100 m at Dongda Mountains in Zuogong County. Species composition and coverage in every sample belts were investigated, and important values of three Kobresia species were calculated in the community based on relative coverage and frequency. At the same time, the epidermal cell shapes of adaxial and abaxial surface were observed, the stomatal length and guard cell width were measured and stomatal density was calculated, so as to observe the adaptability of Kobresia species to the elevation gradient. The results showed: (1) Common features of epidermis were investigated in three species using light microscopy: epidermis was wavy, and stomata apparatus was only distributed in the epidermis of abaxial surface. (2) The stomatal density of all three species presented to be a unimodal pattern along an elevational gradient, and obtained a maximum at the sample belt altitude of 4 537 m. Stomatal density of K. capillifolia (476.4 grasses per mm²) was lower than which of K. humilis (777.6 grasses per mm²), and higher than which of K. macrantha (414.3 grasses per mm²). (3) With the elevational gain, the stomata length of K. humilis(P<0.05)and K. capillifolia significantly increased, and guard cell width of K. humilis and K. capillifolia significantly decreased. By contrast, the stomata length of K. macrantha decreased with the gain of elevation, and guard cell width of which remained basically unchanged (P>0.05). (4)The stomatal density, length and guard cell width of K. humilis and K. capillifolia were significantly correlated with the elevational gradient, and the stomatal characteristics were highly sensitive to the change of elevational gradient, which was consistent with the high importance value in the community. Only stomatal density and length of K. macrantha were significantly correlated with the elevational gradient, and the stomatal characteristics were not highly sensitive to the change of elevational gradient, which was consistent with the low importance value in the community. The correlation between stomatal density, length and guard cell width of Kobresia species and elevational gradient showed the degree of adaptation to habitat at the elevational gradient. It can be seen that the stomatal characteristics of the three Kobresia species have different adaptability to the habitat along the elevational gradient, thus affecting their distribution range and species coverage in the community. K. humilis and K. capillifolia were sensitive to habitat changes, while K. macrantha was insensitive to habitat changes; the guard cell width, like the stomatal length, played an important role in adapting to the habitat.