Drought resistance is influenced by soil water uptake depth in dryland shrubs

Climate change exacerbates aridity in dry shrublands leading to different responses of coexisting shrubs to drought, including different resistance (capacity to sustain growth during droughts). However, it is unknown how resistance depends on shifts in soil water uptake depth and functional traits. To address this issue, we studied seven shrub species in two semi‐arid Mediterranean sites. Using the isotopic composition of oxygen and hydrogen in soil and xylem water samples (δ 18 O, δ 2 H), we quantified depth of soil water uptake. Traits (height, leaf mass per area—LMA and wood specific gravity—WSG) were measured to evaluate whether they were related to intrinsic water‐use efficiency (iWUE) and radial growth resistance to drought. The iWUE was positively correlated with LMA and increased during dry periods in the less arid site. Soil water uptake depth, height and WSG were positively associated with drought resistance. Species that shifted from shallow to deep water sources during the dry season, such as Pistacia lentiscus , Quercus coccifera and Rhamnus lycioides , were more resistant, whereas less resistant species such as Juniperus phoenicea , Juniperus oxycedrus , Rhamnus alaternus and Ephedra spp. used more shallow and stable soil‐water sources. Synthesis. Drought resistance depended on shifts in soil water uptake depth. Drought resistance should be integrated in future analyses of dryland plant communities given its linkages with functional traits.