Distribution Patterns and Assembly Mechanisms of Rhizosphere Soil Microbial Communities in Schisandra sphenanthera Across Altitudinal Gradients

Abstract

To investigate the characteristics of rhizosphere soil microbial communities associated with Schisandra sphenanthera across different altitudinal gradients and to reveal the driving factors of microbial community dynamics, this study collected rhizosphere soil samples at four elevations: 900 m (HB1), 1100 m (HB2), 1300 m (HB3), and 1500 m (HB4). High-throughput sequencing and molecular ecological network analysis were employed to analyze the microbial community composition and species interactions. A null model was applied to elucidate community assembly mechanisms. The results demonstrated that bacterial communities were dominated by Proteobacteria, Acidobacteriota, Actinobacteriota, and Chloroflexi. The relative abundance of Proteobacteria increased with elevation, while that of Acidobacteriota and Actinobacteriota declined. Fungal communities were primarily composed of Ascomycota and Basidiomycota, with both showing elevated relative abundances at higher altitudes. Diversity indices revealed that HB2 exhibited the highest bacterial Chao, Ace, and Shannon indices but the lowest Simpson index. For fungi, HB3 displayed the highest Chao and Ace indices, whereas HB4 showed the highest Shannon index and the lowest Simpson index. Ecological network analysis indicated stronger bacterial competition at lower elevations and enhanced cooperation at higher elevations, contrasting with fungal communities that exhibited increased competition at higher altitudes. Altitude and soil nutrients were negatively correlated with soil carbon content, while plant nutrients and fungal diversity positively correlated with soil carbon. Null model analysis suggested that deterministic processes dominated bacterial community assembly, whereas stochastic processes governed fungal assembly. These findings highlight significant altitudinal shifts in the microbial community structure and assembly mechanisms in S. sphenanthera rhizosphere soils, driven by the synergistic effects of soil nutrients, plant growth, and fungal diversity. This study provides critical insights into microbial ecology and carbon cycling in alpine ecosystems, offering a scientific basis for ecosystem management and conservation.

Keywords: Schisandra sphenanthera; altitude; co-occurrence network; community assembly; soil microorganisms.

Figure 1

Soil physicochemical properties in the rhizosphere soil of Schisandra sphenanthera at different altitude gradients. Note: Different letters indicate significant differences among different altitude gradients (Tukey’s multiple test; p < 0.05). HB1—900 m, HB2—1100 m, HB3—1300 m, HB4—1500 m; the same applies to subsequent figures.

Figure 2

Relative abundance of bacterial and fungal phyla at different altitude gradients. Note: * p < 0.05; ** 0.001 < p < 0.05; *** p < 0.001.

Figure 3

Principal component analysis (PCA) of bacterial and fungal communities at different altitude gradients.

Figure 4

Diversity indices of soil microbial communities. Note: Different letters indicate significant differences between treatments (p < 0.05).

Figure 5

Ecological processes governing soil microbial community assembly. (a–c) Bacterial community assembly is dominated by deterministic processes (heterogeneous selection), with contributions declining at higher elevations. (d–f) Fungal community assembly is driven by stochastic processes (dispersal limitation), decreasing with elevation.

Figure 6

Correlation analysis between nutrient factors and the Beta Nearest Taxon Index (βNTI) of soil microbial communities. Notes: Significance levels: * (p < 0.05); ** (0.001 < p < 0.05). XShannon: Bacterial Shannon index; ZShannon: Fungal Shannon index. XβNTI: Bacterial assembly mechanism; ZβNTI: Fungal assembly mechanism. STC: Soil total carbon; STK: Soil total potassium; STN: Soil total nitrogen; STP: Soil total phosphorus. PTC: Plant total carbon; PTN: Plant total nitrogen; PTK: Plant total potassium; PTP: Plant total phosphorus. SA: Schisandrin A; SB: Schisandrin B.

Figure 7

Co-occurrence network analysis of soil microbial communities. Note: Node size represents the degree (number of connected nodes). Red edges indicate positive correlations, while green edges denote negative correlations. Nodes are color-coded based on taxonomic classification (e.g., phylum). (a–d) represent bacterial networks of HB1–HB4, respectively; (e–h) represent fungal networks of HB1–HB4; (i–l) represent bacterial and fungal combined networks of HB1–HB4.

Figure 8

Relationships between soil physicochemical factors and microbial communities. (a) RDA analysis of the bacterial community. (b) RDA analysis of the fungal community. (c) Structural equation model (SEM) analysis. Note: Red solid arrows indicate significant positive correlations, while green dashed arrows indicate negative correlations. The numbers on the arrows represent standardized path coefficients. STC—Soil total carbon; STK—Soil total potassium; STN—Soil total nitrogen; STP—Soil total phosphorus; PTC—Plant total carbon; PTN—Plant total nitrogen; PTK—Plant total potassium; PTP—Plant total phosphorus; SA—Schisandrin A; SB—Schisandrin B. Significance levels are indicated as * p < 0.05, *** p < 0.001.