Abstract: The density, length and width of stomata are plastic, and these traits can vary with the degree of external stress, and thereby provide an important mechanism for adaptation to variation in environmental factors. In order to survey the typical changes in stomatal characteristics across a moisture deficit gradient in an alpine meadow, eight dominant or common plant species of the alpine meadow in southeast Tibet, were chosen for study, and sites representing a ten-step gradient in soil moisture were identified. The results indicated there are 4 types, based on the degree of water dependency. Kobresia macrantha belonged to a helophyte type, and its stomatal density increased with decreasing soil moisture, but stomatal length and guard cell width decreased. Commelina communis, Rheum pumilum, Kobresia humilis and Polygonum viviparum were a ‘high moisture environment’ type, and the variation in stomatal density, length and guard cell width was typically unimodal across the soil moisture gradient studied. Polygonum macrophyllum and Kobresia capillifolia were species of drier environments, and the variation of stomatal density, length or guard cell width was almost opposite to that of the helophyte type. Stomatal characteristics of Kobresia pygmaea, were not significantly related with soil moisture, and it had a wide distributional range along the soil moisture gradient, hence it is a widely adapted type. Each plant species had its own soil moisture optimum, with growth stress evident at higher or lower soil moisture. In summary, numerous relationships between stomatal characteristics and soil moisture were elucidated.

Key words: stomatal density, guard cells, Kobresia, alpine meadow, gradient of moisture