Regulation of the water status in three co-occurring phreatophytes at the southern fringe of the Taklamakan Desert

We investigated the regulation of the water status in three predominant perennial C3 phreatophytes (Alhagi sparsifolia, Populus euphratica, Tamarix ramosissima) at typical sites of their occurrence at the southern fringe of the hyperarid Taklamakan Desert (north-west China). In the foreland of the river oasis of Qira (Cele), we determined meteorological variables, plant biomass production, plant water potentials (ΨL) and the water flux through the plants. We calculated the hydraulic conductance on the flow path from the soil to the leaves (kSL) and tested the effects of kSL, ΨL and the leaf-to-air difference in the partial pressure of water vapour (Δw) on stomatal regulation using regression analyses. Despite high values of plant water potential at the point of turgor loss, all plants sustained ΨL at levels that were high enough to maintain transpiration throughout the growing season. In A. sparsifolia, stomatal resistance (rs; related to leaf area or leaf mass) was most closely correlated with kSL; whereas in P. euphratica, ∼70% of the variation in rs was explained by Δw. In T. ramosissima, leaf area-related rs was significantly correlated with ΨL and kSL. The regulation mechanisms are in accordance with the growth patterns and the occurrence of the species in relation to their distance to the ground water.

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