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

Aims 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). Methods In the foreland of the river oasis of Qira (Cele), we determined meteorological variables, plant biomass production, plant water potentials (psi(l)) and the water flux through the plants. We calculated the hydraulic conductance on the flow path from the soil to the leaves (k(SL)) and tested the effects of k(SL) psi(L) and the leaf-to-air difference in the partial pressure of water vapour (Delta w) on stomatal regulation using regression analyses. Important Findings Despite high values of plant water potential at the point of turgor loss, all plants sustained psi(L) at levels that were high enough to Maintain transpiration throughout the growing season. In A. sparsitolia, stomatal resistance (r(s); related to leaf area or leaf mass) was most closely correlated with k(SL);. whereas in P. euphratica, similar to 70%, of the variation in r(s) was explained by Delta w. In T. ramosissima, leaf area-related r(s) was significantly correlated with psi(L) and k(SL). 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