Abstract: This paper investigated the stomatal length (SL) and stomatal density (SD) of Rhododendron lapponicum and R. anthopogonoides collected from different altitudes ranging from 2 600 to 3 100 m in Xinglong Mountains. The factors affecting the variations of SL and SD at different altitudes were also analyzed using the data of air temperature, CO2 concentration and terrain. The results showed that SL was decreased but SD increased significantly in leaves of R. lapponicum with the increase of altitude. SL in leaves of R. anthopogonoides was increased at first and then decreased, and SD was opposite. Air temperature and CO₂ concentration were strongly affected by altitude. R. lapponicum acclimatizes mainly the change of temperature and CO₂ concentration by increasing SL and decreasing SD in its leaves, while R. anthopogonoides acclimatizes mainly the change of air temperature, CO₂ concentration and soil moisture content by increasing SL and decreasing SD in its leave.

Key words: Rhododendron, stomatal length, stomatal density, altitude, climate change, Loess Plateau, west Gansu