Developing effective deep-rooted winter wheat cultivars improves adaptation to stored-soil-water irrigation in the North China Plain

Root systems are crucial for soil water uptake in water-limited environments. However, it remains unclear whether winter wheat ( Triticum aestivum L.) cultivar renewal in the North China Plain (NCP) has led to adapted root traits in response to changing irrigation practices, particularly stored-soil-water irrigation (W1). A two-year field experiment was conducted using nine historical winter wheat cultivars (released from 1978 to 2021) under two irrigation regimes: conventional full irrigation (W3) and W1. Root traits, grain yield, water use efficiency (WUE), and evapotranspiration (ET) were analyzed, and the APSIM model was used to simulate the potential for root improvement to enhance grain yield under these regimes. Cultivar renewal significantly increased grain yield by 23 kg·ha −1 ·yr −1 and WUE by 8.2–8.4 g·m −3 ·yr −1 under W1 conditions but did not lead to a concurrent improvement in ET and root traits. In contrast, W1 significantly increased root mass density by 24.5–27.3 % and root length density by 9.7–25.6 % in the 50–150 cm soil layer compared to W3. APSIM simulations demonstrated that optimizing root traits for greater deep-water extraction could substantially boost yield under W1, with a projected increase of 37.5 kg·ha −1 per additional millimeter of water absorbed. We conclude that modern cultivars have improved WUE, but breeding has not strategically enhanced deep root systems to match the needs of water-saving irrigation. Targeted breeding for winter wheat cultivars with more efficient deep roots is crucial to fully leverage the benefits of W1.