| Populus euphratica Oliv.is main constructive specie of desert riparian forest in arid area and it has many important ecological functions, such as bearing the saline and alkaline, resisting drought, wind-break and sand-fixation and so on. Analyzing the changes of the anatomy and hydraulic characteristics in Xylem of populus euphratica under drought stress is significant to interpret its resistance mechanism. This study takes water controlling experiment, and analyzes the reponse of the anatomy and hydraulic characteristics in Xylem of roots, stems, leaves of populus euphratica to different drought stress level. The results show that:(1) There is some response of the anatomy and hydraulic characteristics in roots xylem of populus euphratica to drought stress.With increasing drought stress,for the anatomical structure, the change of vessel density is very significant decreasing(P<0.01); however, the vessel diameter, the thickness and the mechanical strength of vessel wall are very significantly increaseing (P<0.01), perforation diameter and pit diameter are all significantly increasing (P<0.05); however, the micro-morphology of vessel element doesn’t take anything place-there is only one type of vessel:pitted vessel; most of pits are bordered pits and the arrangement type is alternate; all of the perforation are single type. For the hydraulic characteristics, the conductivity (Ks) and the native embolism level (PLC) were a significant increasing trend (P<0.01) with increasing drought stress.(2) There is some response of the anatomy and hydraulic characteristics in stems xylem of populus euphratica to drought stress.With increasing drought stress,for the anatomical structure, the xylem vessel density is very significant decreasing(P<0.01); however, the xylem vessel diameter, the thickness and the mechanical strength of vessel wall are very significantly increaseing (P<0.01), perforation diameter and pit diameter are all significantly increasing (P<0.05); however, the micro-morphology of vessel element doesn’t take anything place-there are two types of vessel:pitted vessel and spiral vessel; most of pits are bordered pits and the arrangement type is alternate; spiral thickening was found on the end wall of the vessel element; all of the perforations are single type. For the hydraulic characteristics, the conductivity (Ks) and the native embolism level (PLC) were a significant increasing trend (P<0.05) with increasing drought stress.(3) There is some response of the anatomy and hydraulic characteristics in leaves xylem of populus euphratica to drought stress. With increasing drought stress, for the xylem anatomical structure, the vessel density in main vein was very significant decreasing(P<0.01); however, the vessel diameter was very significantly increases (P<0.01), and the thickness and the mechanical strength of vessel wall were not significant change (P>0.05). For the hydraulic characteristics, the change of leaves conductivity was a significant increasing trend (P<0.01). In addition, leaf epidermal thickness was significantly increasing (P <0.05); therefore, it reduced transpiration and water losing. Stomata density was significantly increasing(P <0.05), the degree of stomata opening and closing was significant reduction (P<0.01). For the stomata conductance, it appeared "low-high-low" daily variation; besides, it reached maximum at12:00and reached minimum at8:00in morning and evening. Stomata opening and closing maximized to absorb CO2, even more reduced to the lowest level of drought stress. The thickness of palisade tissue was significantly increasing (P<0.01), and the epidermis perpendicular to them; therefore, they avoided to burn from strong light.(4) By comparing of the xylem anatomy and hydraulic characteristics in root, stem and leaf,we can find something. For anatomical structure, the vessel density:stem> leaf> root; vessel diameter:root> leaf> stem; vessel wall thickness:root> leaf> stem; the mechanical strength of the vessel wall:root> stem> leaf; in root xylem and the leaf vein, there was only one type:spiral vessel, but there were two types of vessels: pitted vessel and spiral vessel in stem xylem. For the hydraulic characteristics, there was significant difference among root, stem and leaf. Comparing of the conductivity among them, the result is stem> root> leaf. Comparing of the xylem embolism:root> stem, we found that root is easier to be embolic under drought stress. |
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