# Study on geographic differentiation and environment-host synergistic assembly mechanism of root-associated fungal communities in Paphiopedilum purpuratum

## TL;DR

This study explores how the root fungi of an endangered orchid vary across different locations and how environmental and host factors shape these fungal communities.

## Contribution

The study reveals a synergistic environment-host mechanism in the assembly of root-associated fungal communities in Paphiopedilum purpuratum.

## Key findings

- Root fungal communities showed significant geographic differentiation at family and genus levels.
- Environmental factors, especially longitude, had a stronger influence on fungal community structure than biotic factors.
- Root endophytic fungi were shaped by stochastic processes, while rhizosphere fungi were governed by deterministic processes.

## Abstract

The orchid–fungus symbiosis is fundamental to orchid survival and reproduction; however, the diversity patterns and assembly mechanisms of the root-associated mycobiota in Paphiopedilum purpuratum remain inadequately characterized. We utilized high-throughput sequencing of the internal transcribed spacer 2 region to investigate the composition, diversity, sources, and assembly processes of the endophytic fungal communities across eight geographically distinct populations, with complementary profiling of rhizosphere soil fungi. Our results indicated that Ascomycota constituted the dominant phylum within the root mycobiota, while core taxonomic groups exhibited pronounced geographic differentiation at both family and genus levels. Significant inter-population disparities in α-diversity metrics reflected underlying community compositional divergence. Environmental variables, particularly longitude, exerted a stronger influence on community structure than biotic factors. Approximately 44.05% of root fungal operational taxonomic units were soil-derived, and the host plant selectively enriched fungal taxa, most of which possessed unknown trophic modes. Community assembly processes were compartment-specific: the root endophytic mycobiota was primarily governed by stochastic ecological drift, whereas the rhizosphere communities were predominantly shaped by deterministic dispersal limitation. This compartment-specific assembly was evidenced by the prevalence of stochastic processes (|βNTI| < 2) in the root endosphere, contrasting with the dominance of deterministic processes (|βNTI| > 2) in the rhizosphere. Co-occurrence network analysis revealed higher connectivity and robustness in the endophytic mycobiota. The interaction network between orchid mycorrhizal fungi and other root-associated soil fungi formed an efficient and stable functional system whose complexity showed population-specific differentiation. Collectively, our findings demonstrate clear geographic divergence in the root fungal communities of P. purpuratum and underscore a synergistic environment–host assembly mechanism, thereby providing critical ecological insights for informing conservation strategies for this endangered orchid.

This study investigates the root-associated fungal communities of the endangered orchid Paphiopedilum purpuratum across its geographical distribution. We identified clear geographical differentiation in community composition and diversity, predominantly driven by abiotic factors—particularly longitude—rather than biotic factors. A key finding reveals that 44% of root fungal taxa originate from the soil, indicating active host-mediated selection. A fundamental dichotomy in assembly mechanisms was observed: stochastic ecological drift dominated within roots, whereas deterministic dispersal limitation prevailed in the rhizosphere. Co-occurrence networks demonstrated that the root fungal community is highly connected and robust, suggesting a stable functional system. Our findings elucidate the synergistic roles of environment and host in shaping fungal assembly, providing novel insights into orchid–fungus symbiosis with theoretical implications for mycorrhizal ecology and practical relevance for conservation strategies.