Variations in leaf characteristics of three species of angiosperms with changing of altitude in Qilian Mountains and their inland high-altitude pattern

In this study, 39 leaf samples of three angiosperms (Betula albo-sinensis, tree species; and Caragana jubata and Berberis diaphana, shrub species) were collected in the middle-east parts at 2300-3640 m asl of the Qilian Mountains to study the variations of leaf characteristics of angiosperms with altitude change in inland high-altitude regions of China. Five leaf indexes, viz. epidermal cell density (ED), stomatal density (SD), stomatal index (SI), leaf vein density (VD) and carbon isotopic ratio (delta C-13), were analyzed in laboratory. The results show that there are significant or even very significant linear correlations between the five indexes and altitude, of which SD, SI and VD exhibit a negative correlation with altitude, while ED and delta C-13 exhibit a positive correlation with altitude. Such a correlation assemblage is quite different from the situation in the low-altitude humid environment. Generally, only an assemblage of positive correlations can be observed between the indexes (viz. SD, SI and delta C-13, etc.) and the altitude in the low-altitude humid environment, which were caused mainly by the plants' responses to the change of atmospheric CO2 concentration (C (a) ). However, an assemblage of the negative and positive correlations found here may be attributed mainly to the plants' responses to the change of physiological drought caused by change of low temperature, and here it is preliminarily called the inland high-altitude pattern of plant leaf variations.