Exotic plants can escape from specialist pathogenic microorganisms in their new range, but may simultaneously accumulate generalist pathogens. This creates the potential for pathogen spillover, which could alter plant-competitive hierarchies via apparent competition. To assess the potential for and consequences of pathogen spillover in invaded communities, we conducted a community-level plant-soil feedback experiment in experimental communities that ranged in the extent of exotic dominance, using next-generation sequencing to characterize sharing of putatively-pathogenic, root-associated fungi (hereafter, ‘pathogens’). Exotic plants outperformed natives in communities, despite being subject to stronger negative plant-soil feedbacks in monoculture and harboring higher relative abundance of pathogens. Exotic plants made more general associations with pathogens, making them more prone to sharing pathogens with natives and exerting apparent competition. These data suggest that exotic plants accumulate generalist pathogens that are shared with native plants, conferring an indirect benefit to exotic, over native plants.
DNA-based techniques are increasingly used to assess biodiversity both above- and belowground. Most effort has focussed on bioinformatics and sample collection, whereas less is known about the consequences of mixing collected environmental DNA (eDNA), post-extraction and pre-PCR. We applied varying degrees of pooling to stand-alone eDNA samples collected across a non-native plant invasion density gradient, and compared the fungal communities of pooled and unpooled samples. Pooling soil eDNA decreased observable fungal rarefied richness in our samples, led to phylum-specific shifts in proportional abundance, and increased the sensitivity of detection for the invasive plant’s overall impact on fungal diversity. We demonstrate that pooling fungal eDNA could change the outcome of similar eDNA studies where the aim is to: 1) identify the rare biosphere within a soil community, 2) estimate species richness and proportional abundance, or 3) assess the impact of an invasive plant on soil fungi. Sample pooling might be appropriate when determining larger-scale overarching responses of soil communities, as pooling increased the sensitivity of measurable effects of an invasive plant on soil fungal diversity.