Abstract
Soil degradation from long-term chemical fertilization poses serious challenges to the sustainability of black soil agroecosystems in Northeast China, particularly for the cultivation of medicinal plants such as Aralia continentalis Kitag. To evaluate eco-friendly alternatives, we compared decomposed leaf mulching (LM), conventional fertilization (CF), and an untreated control (CK) in a five-year field experiment. LM significantly improved soil structure by reducing bulk density by 12.8% (p < 0.05) and increasing porosity by 15.6% while enhancing organic carbon and humus fractions by 23.4% and 31.7%, respectively. These changes promoted microbial biomass carbon by 28.2% (p < 0.01) and enriched beneficial fungi such as Mortierella, which correlated with nutrient mobilization and plant growth. Fungal richness and diversity were higher under LM (+18.4% and +12.6%, respectively), whereas CF reduced evenness and favored dominance of stress-tolerant taxa. Functional predictions indicated that LM sustained saprotrophic and symbiotic guilds, while CF weakened mycorrhizal associations. Structural equation modeling identified microbial community composition as a central mediator linking soil properties, microbial diversity, and biomass (R(2) = 0.78), with LM exerting the strongest cascading effects. At the plant level, LM achieved the highest above- and belowground biomass, outperforming CF and CK by 26.3% and 34.5%, respectively. Overall, decomposed leaf mulching represents a sustainable strategy to restore soil quality, enhance microbial diversity, and support medicinal plant cultivation in cold-region agroecosystems.