Aims In the Tarim River Basin of China, desert riparian forest vegetation grows despite the stresses of high temperature and aridity. The species have deep roots that absorb soil water, but a more important reason may be the hydraulic lift (HL) of species. Our aims are to explore whether HL exists in desert riparian vegetation and to determine its ecological impacts.
Methods We studied the HL of Populus euphratica, an important species of desert riparian forest, in September 2008. We used heat ration method (HRM) sap-flow monitoring sensors to measure sap velocity in roots of three trees during four days. Meteorological factors, including wind speed, air relative humidity, leaf temperature and surface temperature, were monitored by a recording weather station. We concurrently sampled and analyzed soil water content by the drying method at six soil depths.
Important findings The sap velocity of tap roots was positive day and night. In contrast, sap flows of lateral roots reversed at night. Soil water content in the subsoil was higher than topsoil in 0-120 cm soil depth and increased with reversed sap flow of lateral roots at night, especially in the 60-120 cm soil depth (soil water content was 28%-38% greater at 4:00 than that at 16:00. Leaf surface vapor pressure deficit can critically affect sap velocity in lateral roots. Hydraulic redistribution has commonly been associated with arid or strongly seasonal environments; our findings prove it also occurs in an extremely arid region of middle Asia.