Road Disturbance Shifts Root Fungal Symbiont Types and Reduces the Connectivity of Plant-Fungal Co-Occurrence Networks in Mountains.

Abstract

Roads are currently one of the most disruptive anthropogenic disturbances to mountain ecosystems worldwide. These disturbances can have a profound effect on roadside soil properties and vegetation, typically favouring fast-growing and ruderal species. However, their effect on plant-associated fungal communities and plant-fungal interactions remains largely unknown. In this study, we examined the changes in root-associated fungal communities as well as plant-fungal and fungal-fungal co-occurrence networks along mountain roads from four biogeographical regions. We found that roadsides consistently altered plant and fungal community composition, generally favouring arbuscular mycorrhizal fungi and putative plant pathogens at the expense of ectomycorrhizal fungi. Moreover, roadsides consistently reduced the complexity of plant-fungal and fungal-fungal co-occurrence networks (with 66%-95% and 40%-94% reduction in total edge density, respectively), even though the richness of fungal communities was not reduced and many of the naturally occurring highly connected taxa were still present. Our findings suggest that altered and transient conditions in the roadsides may favour more generalist symbionts like AMF and pathogens with low fidelity for particular hosts as opposed to surrounding natural vegetation which is dominated by symbionts with higher specificity for the host (like ectomycorrhizal fungi). We conclude that road disturbance may have a consistent negative imprint on connectivity between plants and fungi; a consequence that deserves attention as it could render mountain roadside systems unstable and vulnerable to further pressures such as climate change and invasive species.