Effects of γ-Polyglutamic Acid on Nutrient Availability and Enzyme Activities in Coal Gangue-Based Soil

This study aimed to investigate the effects of γ-polyglutamic acid (γ-PGA) on the physicochemical properties and enzyme activities of coal gangue-based soils, focusing on how different application rates influence soil indicators and enzyme functions for ecological restoration. Soil samples with varying weathering ages were collected from a coal gangue pile, and a pot experiment was conducted with five γ-PGA treatments (0–43.2 g dissolved in 300 mL water). Soil pH, electrical conductivity, nutrient contents, aggregate composition, and enzyme activities (urease and sucrase) were measured, and redundancy analysis (RDA) was applied to evaluate the relationships between soil properties and enzyme activities. γ-PGA rapidly increased soil pH and altered conductivity trends. Its effects on organic matter, nitrogen, phosphorus, and potassium were complex and dependent on both dosage and time. Optimal γ-PGA addition enhanced organic matter and nitrogen transformation, increased potassium availability, and modified water-stable aggregate distribution. Enzyme activities were significantly affected by γ-PGA dosage, exhibiting distinct initial levels and temporal trends across soils of different weathering ages. RDA revealed clear differentiation in soil properties under different treatments, with enzyme impacts evolving over time. DFT results revealed a distinct valence-dominated ion-binding hierarchy, with trivalent cations (Al3+, Cr3+, Fe3+) showing the strongest affinity, followed by divalent cations and monovalent ions/oxyanions. Overall, γ-PGA markedly improves the quality of coal gangue-based soils, providing theoretical guidance and practical reference for ecological restoration and soil management strategies.