Changes of xylem hydraulic efficiency and native embolism of Tamarix ramosissima Ledeb. seedlings under different drought stress conditions and after rewatering

To understand the factors controlling the survival of native Tamarix ramosissima Ledeb. in an extreme drought zone, the Tarim River Basin in northwestern China, we studied the impact of drought stress and water recovery treatments on hydraulic traits. These traits included initial hydraulic specific conductivity (Ks (init)), maximum hydraulic specific conductivity (Ks (max)) and native embolism (PLC, %) of lateral root, main stem and twigs, as well as the xylem anatomical structures of lateral roots and twigs of two-year old T. ramosissima seedlings. Results showed that drought stress and water recovery treatments had significant impacts on Ks (max) value of lateral root, (Ks init) value and native embolism rate of all different organs (p < 0.01). Severely drought stress treatment induced a significant decrease in Ks (init) values of all organs (p < 0.05), however, the values of Ks (max) in lateral root increased significantly (p < 0.01). The native embolism rate increased with the intensity of soil drought stress in all different organ and short-term re-watering had only significant impacts on embolism recovery for lateral roots (p < 0.01), embolism recovered 20% as compared to severely water stressed seedlings. Lateral roots had a larger mean vessel diameter (dmean, dh) and lower vessel density (VD) compared to the twigs, and their Ks (max) values were strongly correlated with xylem vessel diameter.

► Tamarix ramosissima Ledeb. seedlings could change its lateral root maximum hydraulic efficiency under severely drought stress condition.
► Native embolism level of all organs increased with the intensity of drought stress.
► Lateral root embolism recovered for about 20% after re-irrigation.
► Maximum hydraulic efficiency of lateral root and twigs were strongly correlated with xylem vessel diameter.