Fungal and Bacterial Community Dynamics in the Rhizosphere and Rhizoplane of <i>Diabelia spathulata</i> in Relation to Soil Properties

<i>Diabelia spathulata</i>, a rare deciduous shrub native to East Asia, is critically endangered in Korea, yet little is known about its interactions with soil fungal communities. This study presents the first comprehensive analysis of fungal and bacterial communities in the rhizoplane (RP), rhizosphere (RS), and surrounding soil (SS) of <i>D. spathulata</i> in its natural habitat on Mt. Cheonseong, South Korea. High-throughput sequencing of the ITS and 16S rRNA gene regions revealed distinct microbial assemblages across soil compartments. Fungal taxa such as <i>Russula</i>, <i>Trechispora</i>, and <i>Capronia</i> were enriched in RP and RS, highlighting their potential roles in nutrient cycling, organic matter (OM) decomposition, and symbiosis. In contrast, the SS exhibited greater fungal richness but lower specialization. Among bacteria, root-associated compartments were enriched with plant-beneficial genera such as <i>Bacillus</i> and <i>Bradyrhizobium</i>, while bulk soil hosted more generalist taxa. Soil physicochemical analyses showed higher OM and total nitrogen in RS compared to SS, indicating root-driven enrichment. Correlation and network analyses identified strong links between specific fungal and bacterial taxa and key soil properties including pH, OM, and cation exchange capacity. These results suggest that <i>D. spathulata</i> modulates its RS microbiome to enhance nutrient availability and stress tolerance. This study highlights the ecological significance of fungal communities in root-associated microhabitats and provides foundational knowledge for incorporating soil microbiota into conservation and habitat restoration efforts for endangered plant species.