Knowledge about within-species variation in stomatal frequency with varying elevation at very high elevations is rare, which is crucial for us to understand how alpine plants are adapted to the extreme environment. Here, we focus on the variation in stomatal frequency in Kobresia royleana (Nees) Boeckeler (Cyperaceae, Cyperales) along two altitudinal transects (elevation ranges from 3,723 m to 5,081 m) in the center of the Tibetan Plateau. The result shows the stomatal density (SD) varied from 303 ± 55.6 mm^-2 to 542 ± 81.8 mm^-2, and stomatal index (SI) ranged from 21.0% to 29.6%. In contrast with most cases, an unexpected negative response of stomatal frequency to rising elevation was observed. Among abiotic factors, the growing season mean temperature and CO₂ partial pressure significantly declined with increasing elevation, while the growing season precipitation did not vary. Therefore, the decreasing SD and SI were mainly due to the declining temperature rather than the decreasing CO₂ partial pressure. Further, SD and SI were negatively related to leaf functional traits of specific leaf area (SLA), leaf nitrogen concentration (N) and stable carbon isotope ratios (δ¹³C), and all these morphological and physiological traits tended to covary with rising elevation and declining temperature. Meanwhile, the increasing δ¹³C, N and SLA with elevation seem to be strategies for alpine plant to cope with the low-temperature environments. Therefore, the observed covariance between stomatal frequency and leaf functional traits also suggests that the low temperature rather than low CO₂ partial pressure mainly leads to the elevational pattern of stomatal frequency for this alpine species.

在极高的海拔高度上，随着海拔高度的变化，物种内气孔频率变化的知识很少，这对于我们了解高山植物如何适应极端环境至关重要。在这里，我们着眼于青藏高原中心两个海拔高度（海拔从3,723 m至5,081 m）的小嵩草（Nebre）Boeckeler（莎草科，莎草科）气孔频率的变化。结果显示，气孔密度（SD）从303±55.6 mm ^-2到542±81.8 mm ^-2，气孔指数（SI）在21.0％至29.6％之间。与大多数情况相反，观察到气孔频率对升高的上升有出乎意料的负面反应。在非生物因素中，生长期平均温度和一氧化碳₂分压随着海拔的升高而显着下降，而生长期的降水没有变化。因此，SD和SI的下降主要是由于温度下降而不是CO ₂分压的下降。此外，SD和SI呈负比叶面积的叶功能性状（SLA），叶氮浓度（N）和稳定的碳同位素比率（δ相关¹³ C），和所有这些形态和生理性状往往共变与标高上升和温度下降。同时，δ增加¹³C，N和SLA升高似乎是高山植物应对低温环境的策略。因此，观察到的气孔频率与叶片功能性状之间的协方差也表明，低温而不是低的CO ₂分压主要导致了该高山物种气孔频率的升高模式。