XYLEM ANATOMY AND HYDRAULIC TRAITS OF TWO CO-OCCURRING RIPARIAN DESERT PLANTS

Abstract

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 (Ks(max)) and native embolism rate (PLC, %), in the woody shoots and lateral roots (all c. 2–4.5 mm in diameter) of P. euphratica and T. 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, Dh, Dmax), average vessel area (Va), intervessel wall thickness (Tvw), intervessel pit membrane and pit aperture areas (APM, APA), and intervessel pit membrane and pit aperture diameters (DPM, DPA), were larger than in woody shoots (P < 0.05).The mean Ks(max) values in lateral roots were 6–11 times greater than in woody shoots for P. euphratica and T. ramosissima, respectively (P < 0.01). Woody shoots of T. ramosissima had higher native PLC values (68%) than P. 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 T. ramosissima is higher than that of P. euphratica.