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

Abstract

Diabelia spathulata, 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 D. spathulata 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 Russula, Trechispora, and Capronia 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 Bacillus and Bradyrhizobium, 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 D. spathulata 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.

Keywords: Diabelia spathulata; Rhizosphere microbiome; fungal diversity; root-associated fungi; soil properties.

Figure 1.

Alpha diversity analysis and microbial community structures of the 16S rRNA and ITS genes among the RP, RS, and SS groups. Alpha diversity was calculated based on the observed ASV features (left), the Chao1 index (center), and the Shannon index (right) for (A) bacterial; (B) fungal communities. Each boxplot compares alpha diversity across compartments and lines connect paired samples collected from the same plant.

Figure 2.

Beta diversity analysis of the 16S rRNA and ITS genes among the RP, RS, and SS groups. Beta diversity is visualized using NMDS plots (left) and PCoA plots (right), based on the Bray–Curtis index of the (A) bacterial community; (B) fungal community. Each point represents one sample. Clustering patterns represent similarity among microbial communities.

Figure 3.

Relative abundance of bacterial (A); fungal (B) communities among the RP, RS, and SS groups at genus level. Stacked bar plots show the composition of major genera in each compartment. The category “others” includes various low-abundance genera that were grouped together to improve readability of the figure.

Figure 4.

Results of differential abundance analysis of ASVs in bacterial (A); fungal (B) communities among RP, RS, and SS group at the genus level. Bar plots highlight genera showing differences in abundance across compartments. Color bars indicate the compartment in which each genus is relatively more abundant.

Figure 5.

The correlation network among the identified bacterial and fungal genera in soil associated with Diabelia spathulata (r² > 0.7) is presented. Differences in microbial abundance among the RP (red), RS (orange), and SS (yellow) groups are illustrated using pie charts. The size of each pie chart represents the average relative abundance of the respective taxon and pie slices indicate distribution across compartments. Genera with mean relative abundance <0.01% are not labeled. The network consists of 123 nodes and 216 edges.

Figure 6.

Results of correlation analysis of soil properties and bias-corrected observed features of ASVs (r² > 0.6 or <–0.6). The plot shows strong positive or negative correlations between soil physicochemical properties and observed ASV richness in bacterial and fungal communities. Only significant associations are shown.