Synergistic phosphorus fertilization with γ-polyglutamic acid enhances pepper yield via improved root development and...

Low phosphorus (P) use efficiency represents a major constraint in pepper production. Meanwhile, γ-polyglutamic acid (γ-PGA) has been reported to improve nutrient retention and stimulate plant growth. This study evaluated the effects of combined P fertilizer and γ-PGA application on pepper growth, nutrient uptake, yield, and phosphorus use efficiency in pepper plants during entire plant development period.

A two-factor pot experiment was conducted with three P levels (0, 2.0, 4.0 g plant⁻¹) and two γ-PGA concentrations (0, 450 mg L⁻¹). Morphological traits, root architecture, physiological parameters, nutrient uptake, yield, and P use efficiency (PUE) were determined. Data were analyzed using two-way ANOVA, principal component analysis (PCA), and structural equation modeling (SEM).

The results showed that P application alone significantly increased pepper growth, leaf and root traits, total biomass and fruit yield (p < 0.05). Soluble protein, proline, SOD and POD activities were elevated with increasing P supply (p < 0.05), while MDA content was reduced (p < 0.05). P combined with γ-PGA further enhanced plant height, stem diameter, chlorophyll content, biomass and yield (p < 0.05); notably, root surface area increased substantially (p < 0.01). Macronutrient and micronutrient concentrations and accumulations were also significantly improved under combined treatments (p < 0.05). P + γ-PGA further promoted SOD and POD activities (p < 0.05) but weakened CAT activity (p < 0.05), implying distinct ROS quenching pathways. γ-PGA also significantly improved phosphorus use efficiency (p < 0.05). SEM revealed contrasting regulatory pathways: the antioxidant system negatively regulated fruit nutrients via growth traits without γ-PGA, while P + γ-PGA directly enhanced fruit yield (p < 0.05) and indirectly improved fruit nutrients by promoting growth traits (p < 0.05). Moderate P combined with γ-PGA was confirmed as the optimal treatment for pepper growth and yield (p < 0.05).

The combined application of moderate P (2.0 g plant⁻¹) and γ-PGA (450 mg L⁻¹) is the optimal strategy to improve pepper growth, root morphology, nutrient uptake, antioxidant status, fruit yield, and PUE. This strategy provides a practical approach for reducing phosphorus fertilizer input and supporting sustainable pepper production.