Mechanisms of ecological adaptation of Caragana stenophylla to drought stress in different habitats.

To understand the drought stress effects on ecological adaptations of Caragana stenophylla Pojark in different habitats,we selected the sites along the typical steppe,desert steppe and steppe desert from the east to the west on the Ordos Plateau to study morphological characters,anatomical structures and physiological characters of C.stenophylla.The results showed that the stomas located below epidermal cells.The heavier the drought was,the higher the stomatal density was,the higher the stomatal index was,the higher the trichome density was,the thicker the cuticula was,the higher the palisade cells density was.The mesophyll tissue of C.stenophylla varied from ring-palisade to total-palisade as the environment was getting drier from east to west.Physiological characters of C.stenophylla populations in different habitats showed different change laws.Multivariate membership function analysis of physiological characters indicated that drought resistance of C.stenophylla populations in different zones changed from strong to weak with the following order:C.stenophylla in steppe-desert,C.stenophylla in desert-steppe,C.stenophylla in typical steppe.All these study results showed that C.stenophylla plant formed the morphological characters,anatomical structures and physiological characters adaptive to the environment in its long evolution process,which were inherent guarantee of strong adaptability and wide distribution on the Ordos Plateau.