Roots vertical distribution and physiological characteristics in high-yielding and waterlogging-tolerant wheat

• Waterlogging led to a reduction in shoot weight and grain yield, attributed to decreased photosynthetic capacity in older leaves, resulting from the inhibition of root nitrogen assimilation and quantitative traits. • Among the four cultivars, Yangmai25 is considered as the cultivar with both high yield and waterlogging tolerance. • The quantitative traits and nitrogen assimilation of shallow roots while maintaining an appropriate distribution of deep roots will be beneficial for photosynthesis capacity enhancement in leaves and the alleviation of waterlogging-induced yield losses. The comprehensive understanding of root development under waterlogging stress is essential for high-yielding and waterlogging-tolerant wheat cultivars in the scenario of sustainable production in high-precipitation regions. A pot experiment was conducted to investigate the vertical distribution and physiology of root systems in the four commercial wheat cultivars (Yangmai24, Ningmai13, Ningmai9, and Yangmai25) which exhibit diverse grain yield and waterlogging tolerance. The results indicated that waterlogging stress caused a reduction of 21.5% in grain yield, 34.4% in root weight, and 34.5% in root length. Among the four cultivars, Yangmai25 exhibits both high yield and waterlogging tolerance, with only 11.8% grain yield reduction. Yangmai25 had the lowest shallow (0–20 cm) root weight percentage but the highest deep (60–100 cm) root weight percentage at maturity. These findings indicate that Yangmai25 maintained a numerous root system and balanced vertical growth pattern. Waterlogging stress inhibited the vitality and nitrogen assimilation efficiency in shallow roots, but high yield cultivars, Yangmai25 and Ningmai9, sustained significantly higher levels of these traits. Moreover, waterlogging significantly reduced the area and photosynthetic rate ( Pn ) of older leaves. Among the tested cultivars, Yangmai25 displayed the largest flag leaf area, potentially contributing to its strong photosynthetic capacity. Further analysis indicates that greater root weight and length significantly enhanced shoot biomass and grain yield, primarily through increased Pn of the top leaves. The P n levels in the top two leaves mainly depended on the weight, length, vitality, nitrogen assimilation efficiency of shallow roots, and the 3 rd leaf P n was associated with an increased distribution of deep roots. This study indicated that improving the quantitative traits and nitrogen assimilation of shallow roots while maintaining an appropriate distribution of deep roots will be beneficial for photosynthesis capacity enhancement in leaves and the alleviation of waterlogging-induced yield losses, offering a novel perspective on achieving high and stable wheat production.