Abstract: Reeds are widely distributed in drought and high salt conditions of northwestern China.Leaf epidermal micromorphology,anatomy,chloroplast ultrastructure and physio-chemical characteristics due to long-term adaptation in the natural habitats of common reed (Phragmites communis Trin.) contrasted considerably among three different ecotypes:dune reed (DR),Gobi salt reed (GSR) and swamp reed (SR).The main objective of the present study is to determine the adapting characteristics of morphology,anatomy and physiological responses of thin roots in DR,GSR and SR.The results show that root length density was higher in SR and few root hairs were observed in DR.Cross-section anatomical features show that each ecotype has an endodermis and exodermis,while cortex thickness and proportion of root cortical aerenchyma and stele in root structure varied among the three ecotypes.The stele and xylem share a larger area in DR compared to GSR and SR.GSR has a large proportion of the cortex with radialized distribution of aerenchyma cells spacing,and the cortex has a peripheral,mechanically stiff ring in the exodermis.SEM and TEM microscope images show that GSR has a sclerenchyma ring with high lignification in the exodermis.The physio-chemical parameters show that GSR had a higher level of stress tolerance than DR.These findings indicate that developed water-absorbing tissues were largely distributed in the root structure of DR,and a main framework with supporting function spacing with aerenchyma was dominant in GSR in the long term adaptation to their natural habitats,respectively.

Key words: Phragmites communis, ecotype, root morphology, cross-section anatomy, physio-chemical parameters