Biochar–Dolomite Co-Application Alleviates Soil Functional Decline Under Continuous Ganoderma lingzhi Cropping and Promotes Quality Formation

Soil degradation caused by continuous cropping has become a major constraint on stable Ganoderma lingzhi production, while biochar–mineral amendments are commonly used to restore degraded soils. However, the specific effects of continuous cropping on Ganoderma lingzhi production and soil functions, as well as the potential of co-application to restore its yield and quality, remain unclear. A Ganoderma lingzhi microcosm system was established with first-cropping, continuous-cropping, and different biochar–dolomite treatments. Soil physicochemical properties, enzyme activities, microbial communities, yield, quality traits, and heavy metals were evaluated. Continuous cropping significantly reduced soil pH, organic carbon, total nitrogen, available nutrients, microbial diversity, and Ganoderma lingzhi yield. Fruiting-body dry weight and triterpenoid content declined by 20.09% and 24.62%, respectively. Biochar–dolomite co-application effectively alleviated the adverse effects of continuous cropping. Compared with other co-application treatments, the 30% biochar + 70% dolomite treatment showed strong overall recovery capacity. Compared with continuous cropping, this treatment increased fruiting-body biomass by up to 54.81% and triterpenes by up to 75.57%. Different co-application ratios produced distinct ecological regulation patterns: the dolomite treatment favored soil pH elevation, available nutrient and S-NPH accumulation, and sporulation; the biochar treatment showed advantages in S-UE activity and heavy metal control; and the 70% biochar + 30% dolomite and 50% biochar + 50% dolomite treatments regulated carbon transformation processes and microbial community recovery, respectively. Co-application also increased microbial richness and diversity and reshaped community structure. Structural equation modeling indicated that the amendments strengthened positive links among soil nutrients, the ionic environment, microorganisms, enzyme activities, and Ganoderma lingzhi quality, revealing a potential nutrient and ionic environment-microorganism-enzyme-Ganoderma lingzhi quality pathway. In summary, biochar–dolomite co-application alleviates the continuous cropping obstacle of Ganoderma lingzhi and improves its yield and functional quality by improving the soil physicochemical environment, promoting humus accumulation, and reshaping microbial community structure, providing a theoretical basis for quality improvement of medicinal fungi and soil ecological regulation under continuous cropping.