Elevating crop productivity and sustainability: The role of organic fertilizers in shaping wheat's nitrogen economy and photosynthetic response

Organic fertilizer, as a sustainable alternative, enhanced soil and nutrient quality, as well as crop nitrogen use efficiency (NUE) and photosynthetic rate (Pn). Previous studies have emphasized soil mechanisms but lacked research on the physiological mechanisms of photosynthesis and the microenvironment in the field, particularly regarding their interrelationships. To investigate the effects of substituting organic fertilizer for chemical fertilizer at varying ratios on wheat’s nitrogen physiological use efficiency (NPUE), photosynthetic mechanisms, and yield, a three-year field trial was conducted in Shaanxi, China. The trial quantified photosynthetic and related physiological indicators, employing both nitrogen allocation models and structural equation models to analyze the regulatory mechanisms by which organic fertilizers influence wheat’s nitrogen economy and photosynthesis. Organic fertilizers substitution significantly increased wheat yield by 35.6 %, primarily through increased panicle number. This yield enhancement became more pronounced with increased application duration. A 35 % ratio of organic fertilizers improved NUE by 22.8–26.0 % and photosynthetic nitrogen use efficiency (PNUE) by 10.3–14.9 %, compared to the control. Organic fertilizers enhanced Pn and PNUE by increasing nitrogen allocation within the photosynthetic system, particularly in the carboxylation and electron transport systems. Under nitrogen stress, wheat maximized its photosynthetic capacity by increasing nitrogen to photosynthetic components. Additionally, organic fertilizers slightly elevated field CO 2 concentrations, although this did not significantly alter nitrogen allocation patterns in the photosynthetic system, it directly boosted photosynthesis. In conclusion, organic fertilizer substitution enhanced yield and NUE by optimizing photosynthetic nitrogen allocation during the grain-filling stage, with prolonged application further amplifying these benefits. These findings provide theoretical support for the "organic fertilization-driven nitrogen enhancement" strategy. • Organic fertilizer combined with inorganic fertilizers increased wheat yield. • The yield enhancement became more pronounced with increased application duration. • Organic fertilizer enhanced nitrogen allocation within the photosynthetic system. • Organic fertilizer increased carboxylation and electron transport system N allocation. • Field CO 2 changes had no significant effect on N allocation in photosynthetic system.