Soil profile thickness governs water use strategies in riparian jujube trees

Understanding plant water use patterns in agricultural riparian ecosystems is essential for sustainable water management under climate change. Due to sedimentary processes, soil profile thickness increases with distance from the riverbank. However, the mechanisms governing how plants adjust their water acquisition patterns across riverbank distance gradients remain inadequately explored. This study investigated jujube trees ( Ziziphus jujuba Mill.)‌ at three sites representing increasing distances (near, intermediate, far) from the Yellow River, with soil profile thicknesses of 50 cm, 80 cm, and 120 cm respectively. Using δ 2 H and δ 18 O to quantify the water source contributions and δ 13 C to assess water use efficiency and drought stress, we quantified groundwater/river water dependency, identified key drivers of soil water uptake and assessed drought stress levels. The results showed that trees at far sites relied significantly less on groundwater/river water compared to those at near and intermediate sites. Across all sites, groundwater/river water utilization was inversely correlated with soil profile water content, indicating preferential soil water uptake. For soil water absorption, trees at all sites preferentially absorbed from soil layers with higher fine root proportion. Additionally, trees at near and intermediate sites exhibited flexible soil water absorption, with uptake positively correlated to the water content of the corresponding soil layer, whereas trees at far sites maintained fixed uptake depths regardless of water content variation. Due to constrained groundwater/river water access and fixed soil water uptake strategies, trees at far sites displayed the highest water stress and water use efficiency, as indicated by elevated leaf δ 13 C values. These results highlight soil profile thickness as a critical factor determining plant water use strategies in agricultural riparian systems, with implications for distance-based water management to maintain ecological stability and agricultural productivity along riverbank. Graphical summary of water use strategy for the jujube at different distance from the Yellow Riverbank. The blue arrow indicates water use efficiency, yellow arrow denotes soil water uptake plasticity, and black arrow represents groundwater/river uptake, with darker color indicating higher values. • Soil profile thickness is a critical governing factor for riparian jujube water use strategies. • Far-site trees rely less on groundwater/river water and exhibit fixed soil water uptake depths. • Near/intermediate-site trees show flexible water uptake, correlated with soil water content. • Far-site trees face stronger drought stress and higher water use efficiency.