Soil Chemistry and Microbial Community Patterns Across <i>Tricholoma matsutake</i> Fairy-Ring Developmental Stages in Yeongju, South Korea

This study investigates how shiro developmental stages, soil physicochemical properties, and seasonal variation shape fungal and bacterial communities associated with <i>Tricholoma matsutake</i> in a <i>Pinus densiflora</i> forest in Yeongju, South Korea. Seasonal soil samples from past, present, and future shiro zones were analyzed using ITS and 16S rRNA metabarcoding together with soil chemical measurements. Shiro-driven spatial heterogeneity, rather than seasonality, was the dominant factor structuring microbial communities. Fungal assemblages differed significantly among shiro stages, with exchangeable potassium (K⁺) emerging as the primary driver and a strong predictor of <i>T. matsutake</i> abundance. Elevated K⁺ in active shiro zones corresponded to reduced fungal diversity, suggesting competitive exclusion by dominant ectomycorrhizal taxa. In contrast, bacterial communities were shaped mainly by water-soluble iron (Fe), shifting from Acidobacteria-rich assemblages in past zones to Proteobacteria in active zones. The enrichment of siderophore-associated taxa suggests a potential role of Fe acquisition processes, broadly consistent with mechanisms proposed in the mycorrhiza helper bacteria hypothesis, though not directly tested here. Overall, <i>T. matsutake</i> development generates nutrient-specific biogeochemical gradients-K⁺ for fungi and Fe for bacteria-that reorganize soil microbial communities. These findings underscore tightly linked biotic-abiotic interactions in shiro ecology and highlight microbial and chemical features that may serve as indicators of shiro activity.