干旱区生态环境知识资源中心

Populus euphratica Oliv. and Tamarix ramosissima Ledeb. are the dominant riparian plants in desert ecosystems in China, where they play a significant role in maintaining ecological balance. To obtain a better insight into the ecological adaptations of xylem structure and hydraulic traits in desert phreatophytes to extremely drought-stressed environments, we investigated various quantitative features of the vessels and intervessel pits, as well as the xylem hydraulic efficiency (K-S(MAX)) and native embolism rate (PLC, %), in the woody shoots and lateral roots (all c. 2-4.5 mm in diameter) of Populus euphratica and Tamarix ramosissima from natural populations in the Heihe River Basin, northwestern China. The relationships between xylem anatomy and hydraulic traits are also discussed. There were significant anatomical differences between lateral root and woody shoot xylem within individual species. For lateral roots, arithmetic, hydraulic and maximum vessel diameter (D, D-H, D-MAX), average vessel area (V-A), intervessel wall thickness (T-vw), intervessel pit membrane and pit aperture areas (A(PM), A(PA)), and intervessel pit membrane and pit aperture diameters (D-PM, D-PA), were larger than in woody shoots (P < 0.05). The mean K-S(MAX) values in lateral roots were 6-11 times greater than in woody shoots for Populus euphratica and Tamarix ramosissima, respectively (P < 0.01). Woody shoots of Tamarix ramosissima had higher native PLC values (68%) than Populus euphratica (39%). The different vessel grouping patterns in the two species seemed to be related to their different native embolism level. It is possible that the lateral roots of these two riparian desert plants could be more resistant to embolism than the woody shoots, and that cavitation resistance in the root xylem of Tamarix ramosissima is higher than that of Populus euphratica.