Xylem anatomy and hydraulic conductivity of three co-occurring desert phreatophytes

The tree species Populus euphratica, the shrub Tamarix ramosissima and the sub-shrub Alhagi sparsifolia are phreatophytes that grow along the southern fringe of the Taklamakan Desert (NW China). We hypothesised that in the shoot xylem of these species, the fraction of conduits with a large cross-sectional area and the hydraulic conductivity decrease in the sequence A. sparsifolia > T. ramosissima > P. euphratica according to the different ground water distances at the typical sites of the species' occurrence. The theoretical hydraulic conductivity related to the total cross-sectional xylem area (kttot) or to the cross-sectional area of the conduits (ktcond) was computed using a modified Hagen-Poiseuille equation. The percentage of wide conduits and ktcond were highest in A. sparsifolia, and smallest, in P. euphratica. With regard to kttot, the diffuse-porous to semi-ring-porous P. euphratica occupied an intermediate position due to an increased percentage of conducting area related to the total cross-sectional xylem area. This figure as well as kttot were lowest in the semi-ring-porous to ring-porous T. ramosissima. The kttot values corresponded to the leaf area-related hydraulic conductivity calculated from measurements in the field. Altogether, our results match the typical occurrence of the species with respect to the ground water depth.

Research highlights► We studied wood anatomy and hydraulic conductivity in three desert phreatophytes. ► The sub-shrub Alhagi sparsifolia exhibited the largest percentage of wide conduits. ► Hydraulic conductivity (kt) concurred with the percentage of wide conduits. ► Theoretical kt corresponded to values calculated from field measurements. ► The results match the species' occurrence with respect to the ground water depth.