Abstract: The physiological process and the mechanism of drought-resistance of Pinus sylvestris var.mongolica seedlings were studied at different irrigation levels. The results showed that of photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency, leaf temperature and other water status index varied regularly with the different irrigation levels. Irrigation levels of 409.2 and 189.2mm had obvious effect on the seedlings.The difference of effect on seedlings between 409.2 and 321.2mm or between 321.2 and 189.2mm was not obvious. The mechanism of drought-relief of the seedlings was anti-dehyration.

Key words: Oasis-desert ecotone, Vegetation coverage, Soil factors, Spatial heterogeneity