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.

Changes in biodiversity reflect processes acting at multiple spatial scales, including globally, among habitats and within communities. This complexity makes it difficult to analyse the mechanisms that change biodiversity over time. To resolve this, we propose a novel approach to partition temporal changes in biodiversity into contributions from selection at multiple scales. We apply this approach to study changes in the biodiversity of invertebrate herbivores from a large-scale, plant community experiment. Though the experiment was designed to foster distinct insect communities due to differences in host plants, our approach shows that selection among these treatments was a negligible facet of diversity change. Instead, the dominant source of community dynamics was rapid changes in the relative abundances of individual species. These shifts produced surprisingly small changes in biodiversity. More broadly our work highlights how total change in biodiversity across a biogeographic region can be partitioned into logically distinct mechanisms.

The criteria by which plants select symbiotic partners are largely unknown, but functional complementarity of partner traits could be important to symbioses such as arbuscular mycorrhizas. Specifically, coarse-rooted plants are more likely to be limited by nutrient diffusion compared with fine-rooted plants, and therefore more reliant on fungi that can compensate with traits that maximize soil exploration. However there remains no evidence directly linking plant root traits and fungal functional traits. We transplanted the root microbiome of 30 native and exotic plant species ranging in root diameter, onto an unrelated host plant species in multi-compartment pots. We then quantified fungal hyphal exploration and characterized the fungal community near and far from roots. We found that arbuscular mycorrhizal fungi from coarse-rooted plants produced more hyphal biomass and explored further away from the plant roots. This study provides the first evidence of functional complementarity between plant roots and arbuscular mycorrhizal fungi.

Changes in biodiversity reflect processes acting on the success of individual species at multiple spatial scales, including in communities, biogeographic regions, and globally. This complexity makes it difficult to analyse the mechanisms shaping diversity change using traditional approaches. To resolve this, we propose a novel approach to partition total biodiversity changes according to mechanisms reflecting species' success at multiple scales. We apply this approach to study changes in the diversity of invertebrate herbivores from a large-scale, plant community experiment. This partitioning showed that rapid changes in the relative abundances of individual species resulted in surprisingly small changes in diversity across scales. Our novel analytical method reveals how strong ecological effects at different hierarchical levels can counteract each other, resulting in weak effects on diversity across broad spatial scales.

A document by Ian Dickie. Click on the document to view its contents.

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.