Structural and Functional Responses of Root Endophytic Fungi to Fairy Ring Expansion in Alpine Meadows on the Tibetan Plateau.

Fairy rings (FRs) are potent ecosystem engineers that reshape soil environments, yet the response of root endophytic fungi (REF) to these perturbations remains less understood. Here, we characterized REF communities in Kobresia humilis across three FR types-Type I (injurious Agrocybe sp.), Type II (promoting Agaricus campestris), and Type III (neutral Clitocybe sp.)-on the Tibetan Plateau. Our data suggest that, unlike rhizosphere microbial communities that are often influenced by host recruitment, REF communities may be more strongly shaped by interactions among fungal taxa. Specifically, we observed a consistent decline in the relative abundance of putatively beneficial fungal groups, including Glomeromycetes and Archaeorhizomycetes, within fungal-active (ON) zones. We propose the term "Symbiotic Decoupling" as a conceptual hypothesis to describe this pattern, whereby FR expansion may be associated with a reduced representation of these taxa in root endophytic fungal communities. This pattern may be consistent with different ecological trade-offs associated with contrasting FR environments. In promoting Type II rings, elevated nutrient availability (e.g., phosphorus) coincided with a simplified network topology. This pattern is consistent with the hypothesis that increased nutrient availability may reduce the relative importance of certain symbiotic associations, a concept we tentatively refer to as "Resource-driven Intensification". Conversely, the T1 network displayed a comparatively denser topology; however, because the inferred networks differed in node and edge numbers, these differences should not be interpreted as direct quantitative evidence of greater connectivity. This pattern may indicate increased coordination among community members under stressful conditions and is consistent with a conceptual framework that we term "Defensive Complexity". However, the functional significance of this network configuration remains to be experimentally validated. Collectively, these findings suggest that FR expansion may alter the balance between host-associated filtering processes and fungal community interactions, potentially resulting in community configurations that favor rapid resource acquisition or persistence over the maintenance of previously dominant symbiotic taxa.