Lithology Controls on Arbuscular Mycorrhizal Fungi Across Bulk Soil and Rock–Soil Interface

Arbuscular mycorrhizal fungi (AMF) are vital for nutrient cycling, but how lithology across bulk soil and the rock–soil interface influence AMF communities remains poorly understood. We investigated the effects of karst (dolomite, limestone) and non-karst (clastic rock) lithologies across bulk soil and the rock–soil interface on AMF diversity, community composition, and co-occurrence networks in southwest China. AMF diversity did not differ among lithologies or between bulk soil and rock–soil interface, whereas community composition showed significant differences across lithology. The relative abundance of Glomus was lower in karst than in non-karst, whereas Paraglomus showed the opposite pattern. Co-occurrence network analysis revealed that karst soils exhibited higher numbers of nodes and edges but lower network density, transitivity, betweenness centrality, and average path length compared to non-karst soils. Within the same dolomite and limestone, network properties were similar between the rock–soil interface and bulk soil. Soil pH, exchangeable Ca2+ and Mg2+, total nitrogen, and nitrate nitrogen were negatively correlated with Glomus and network properties (e.g., number of nodes and edges), while ammonium nitrogen showed positive correlations. Our results indicate that lithology exerts a stronger influence than soil compartment on AMF community composition and interspecific interactions, emphasizing the key role of lithological substrates in regulating AMF communities.