Xylem hydraulic conductivity and embolism in riparian plants and their responses to drought stress in desert of Northwest China

Riparian plants in the lower reaches of the Tarim River (Tikanlik) and Heihe River (Ulan Tug) were selected as study objects, where they suffered from different drought stresses. The differences of root and twig xylem hydraulic conductivity and embolism of the typical riparian plants, including Populus euphratica, Tamarix spp., Alhagi sparsifolia and Karelinia caspica, and their responses to drought stress were analysed. The results showed that (1) the riparian plants in the lower Tarim River suffered from more severe drought stress than those in the lower Heihe River because of their lower xylem hydraulic conductivity, and the fundamental reason resulted in different degrees of drought stresses in the two regions was groundwater depth; (2) the drought resistance of Tamarix spp. was the strongest, which could exist in a broad habitat with different degrees of water stresses, whereas A.sparsifolia and K. caspica only exist in a narrow habitat with groundwater depth less than 4m because of their weak drought resistance; and (3) the main resistance part of water transportation of riparian plants was twig xylem when they encountered the mild drought stress, whereas it was root xylem when the riparian plants encountered severe drought stress, and riparian plants adapted the mild drought stress through limiting twig xylem hydraulic conductivity to coordinate the plant growth, while they adapted the severe drought stress through enhancing xylem hydraulic conductivity of dominant branches with strong competitiveness of sap flow and sacrificing non-dominant branches to improve the plant survival chance. Copyright (c) 2013 John Wiley & Sons, Ltd.