Organic Mulching for Sustainable Soil Management in Grifola frondosa Cultivation: Differential Effects on Soil Properties, Microbiome, and Enzyme Functions

The yield and quality of the edible fungus Grifola frondosa are highly dependent on its casing soil environment. This study aimed to investigate how different organic mulching materials, including organic fertilizer, pine needles, wheat straw, and bamboo leaves, differentially affect the physicochemical properties, microbial biomass, enzyme activities, and microbial community structure of the casing soil, in order to provide a scientific basis for sustainable soil management in Grifola frondosa cultivation. A field experiment was conducted with six treatments: initial soil (CK), non-mulched casing soil, and four mulched treatments. Soil samples were analyzed using high-throughput sequencing (16 S rRNA and ITS) for bacterial and fungal communities, alongside conventional biochemical assays for nutrient content, microbial biomass, and enzyme activities. Compared with the non-mulched casing soil (Soil Only) treatment, organic fertilizer mulch significantly (p < 0.05) increased total nitrogen (1.85 g kg⁻¹), available phosphorus (17.37 mg kg⁻¹), soil organic matter (61.34 g kg⁻¹), microbial biomass carbon (256.61 mg kg⁻¹), and dehydrogenase activity (1765.37 µg g⁻¹ d⁻¹). Bamboo leaves mulch specifically enhanced fungal diversity (Chao1 index = 1285.52) and urease activity (4516.05 µg g⁻¹ d⁻¹) (p < 0.05), while wheat straw mulch resulted in the highest available potassium content (426.33 mg kg⁻¹) (p < 0.05). Soil nutrients and enzyme activities were strongly correlated with shifts in dominant microbial phyla such as Acidobacteriota and Ascomycota (p < 0.05). Different organic mulches reshape the casing soil environment through distinct functional pathways. These findings demonstrate that organic amendments can be selectively used as soil management tools to improve soil health, nutrient cycling, and sustainability in Grifola frondosa cultivation systems.