Optimized nitrogen management enhances lodging resistance by modulating stem physicochemical traits in oats

BACKGROUND: Oat (Avena sativa L.) is a critical dual-purpose crop for grain and forage, yet its yield potential is frequently constrained by stem lodging exacerbated by sub-optimal nitrogen (N) management. While the general physiological basis of lodging is known, the precise quantitative contributions of specific stem physicochemical traits under varying N regimes remain underexplored, particularly in unique high-altitude agroecosystems. To address this gap, we conducted a two-year field trial (2018-2019) in the rain-fed Qinghai-Tibet Plateau, evaluating two oat cultivars with contrasting lodging resistance (LENA, resistant; QY2, susceptible). Across six N rates (0, 60, 120, 180, 240, and 300 kg·ha⁻¹), we quantified structural components (lignin, cellulose), non-structural carbohydrates (soluble sugars, starch), and mineral elements (Ca, K, Si, Mg) in the second basal internode at the milk stage. Key determinants of stem strength were isolated using hierarchical partitioning, structural equation modeling (SEM), and TOPSIS analysis. RESULTS: Lodging severity and stem physicochemical profiles were significantly driven by N rate, genotype, and their interaction. Increased N application elevated soluble protein levels but concurrently suppressed the accumulation of lignin, cellulose, and key minerals (Si, Ca, K). Hierarchical partitioning identified Ca, K, Si, soluble sugars, and lignin as the primary determinants, collectively explaining 87% of the variance in the lodging index. Furthermore, SEM revealed that genotype and high N inputs indirectly exacerbated lodging risk by downregulating the accumulation of these critical structural and mineral components. Total standardized effects on the lodging index were - 0.209 (genotype), 0.310 (N rate), and 0.156 (interaction). CONCLUSIONS: . These findings provide a physiological framework for rational nitrogen management and offer novel mechanistic insights into oat lodging resistance.