Screening of low-nitrogen tolerant winter wheat cultivars: integrated evaluation from hydroponics to the field

The excessive application of nitrogen fertilizers has resulted in significant environmental pollution and economic losses while decreasing nitrogen use efficiency in wheat. This study comprehensively evaluated low-nitrogen (LN) tolerance across 77 winter wheat cultivars through integrated field trials and hydroponic experiments. Field assessments over two growing seasons evaluated eight yield-related traits under high-nitrogen (HN: 270 kg/ha) and LN (0 kg/ha) conditions, while hydroponic screening assessed ten seedling phenotypic parameters under HN (4 mmol/L) and LN (0.4 mmol/L) treatments. Principal component analysis and the membership function method were used to generate a comprehensive LN tolerance index (CLNTI), categorizing cultivars into four types: highly tolerant (HT), moderately tolerant, moderately sensitive, and highly sensitive (HS). A strong correlation was observed between field and hydroponic evaluations, with three cultivars consistently displaying HT characteristics. Under LN stress, all cultivars exhibited decreased plant height, flag leaf size, light utilization capacity, and nitrogen metabolism enzyme activities. However, HT cultivars maintained substantially higher physiological activity compared with HS cultivars, demonstrated by larger flag leaves, superior chlorophyll fluorescence parameters, and elevated relative chlorophyll content, along with enhanced activities of nitrate reductase, glutamine synthetase, and glutamate synthase. Notably, HT cultivars developed enhanced root architecture under LN condition, characterized by increased total root length, root surface area, and tip number—adaptations not observed in HS cultivars, which exhibited root trait reductions. These results indicate that HT wheat optimizes root morphology for nitrogen acquisition, maintains nitrogen assimilation enzyme activities, and sustains stable photosynthetic efficiency to minimize yield reduction. • A comprehensive low-nitrogen tolerance evaluation system was established for 77 winter wheat cultivars, integrating field and hydroponic data. • Tolerance arises from superior root architecture, sustained nitrogen metabolism (NR,GS,GOGAT), and stable photosynthesis under stress. • Three cultivars were consistently identified as highly tolerant, exhibiting minimal yield loss under low-nitrogen conditions.