Proline-2′‐deoxymugineic Acid Enhances Iron Utilization, Yield, and Seed Quality of Soybean Grown in Calcareous–Alkaline Soils

Iron (Fe) deficiency is a major constraint to crop production in calcareous–alkaline soils due to low Fe bioavailability, resulting in reduced growth, yield and seed nutritional quality. This study evaluated whether metal-free proline-2′-deoxymugineic acid (PDMA) can improve Fe utilization efficiency by enhancing rhizosphere Fe availability, thereby sustaining growth, yield formation, and seed nutritional quality in an Fe deficiency chlorosis (IDC)-sensitive soybean cultivar grown under calcareous–alkaline conditions. Soybean plants were cultivated in calcareous–alkaline soil and treated with PDMA at three application rates (3, 15, and 30 µM), with Fe-EDDHA and untreated controls included for comparison. Physiological traits, expression of Fe uptake and transport genes, micronutrient concentrations in roots, leaves, and seeds, yield components, and seed protein and oil contents were determined. PDMA alleviated Fe deficiency symptoms in a dose-dependent manner by attenuating root Fe deficiency responses and modulating the expression of key Fe uptake and transport genes. These changes were associated with improved chlorophyll status and enhanced vegetative growth under alkaline stress. Higher application rates increased the accumulation of Fe and other micronutrients in plant tissues and significantly improved yield components, seed yield, and seed nutritional attributes. In several agronomic and quality-related parameters, PDMA performed comparably to or better than Fe-EDDHA. These findings demonstrate that metal-free PDMA improves Fe utilization efficiency by enhancing rhizosphere Fe availability, thereby sustaining growth, yield formation, and seed nutritional quality in soybean grown on calcareous–alkaline soils, and offering a sustainable, eco-friendly alternative to conventional iron chelation strategies.