Abstract. Current understanding of acclimation processes in desert-shrub species to drought stress in dryland ecosystems is still incomplete. In this study, we measured sap flow in Artemisia ordosica and associated environmental variables throughout the growing seasons of 2013–2014 (May–September period of each year) to better understand the environmental controls on the temporal dynamics of sap flow. We found that the occurrence of drought in the dry year of 2013 during the leaf-expansion and leaf-expanded periods caused sap flow per leaf area (Js) to decline significantly, resulting in a sizable drop in transpiration. Sap flow per leaf area correlated positively with radiation (Rs), air temperature (T), and vapor pressure deficit (VPD), when volumetric soil water content (VWC) was > 0.11 m3 m−3. Diurnal Js was generally ahead of Rs by as much as 6 hours. This lag time, however, decreased with increasing VWC. Relative response of Js to the environmental variables (i.e., Rs, T, and VPD) varied with VWC, Js being more biologically controlled with low decoupling coefficient and thus being less sensitive to the environmental variables during dry periods. According to this study, soil moisture is shown to control sap-flow (and, therefore, plant-transpiration) response in Artemisia ordosica to diurnal variations in biophysical factors. The findings of this study add to the knowledge of acclimation processes in desert-shrub species under drought-associated stress. This knowledge is essential to model desert-shrub-ecosystem functioning under changing climatic conditions.
Soil moisture control on sap-flow response to biophysical factors in a desert-shrub species, <i>Artemisia ordosica</i>