Diversity and function of the soil microbiome in a North American forest in response to Alliaria petiolata (garlic mustard) invasion.

Abstract

The disruption of soil microbial communities is thought to be a major contributor to the expansion of invasive plants. Previous research has focused on identifying how invasive plants change soil microbial diversity and composition. However, microbes with different functions vary in their response to environmental changes, which in turn can affect plant community composition and ecosystem function. Thus, it is important to recognize the different functional roles of genetically distinct microbe taxa to understand the impact of plant invasion on nutrient cycling and other ecosystem services. Alliaria petiolata is an invasive plant in North America from Eurasia that has the potential to negatively affect the beneficial mutualism between native plants and arbuscular mycorrhizal fungi (AMF) through the production of allelopathic compounds belowground. Despite mounting evidence for such an effect under controlled laboratory experiments, it is less clear if it persists under natural field conditions. Additionally, the potential effect of A. petiolata on non-mycorrhizal fungi and bacteria remains to be determined. Molecular tools have emerged that can both characterize the taxonomic diversity of soil microbiota and their functions to an unprecedented level of resolution. To investigate the effect of A. petiolata on the soil microbiome diversity and function I combined molecular and field data. I used high throughput sequencing of genomic DNA encoding for the ITS and 16S region of ribosomal RNA to determine impact of A. petiolata invasion on the structure of fungal and bacterial communities in field soils. Functions were assigned to the microbes that varied in their composition with invasion. I also measured root health of native plants co-occurring with A. petiolata to determine correlations between functional groups of soil microbial communities and plant health. Overall, my findings suggest that mycorrhizal suppression is not a particularly strong mechanism to explain the invasion success of A. petiolata. In fact, changes in AMF community composition do not persist under natural field conditions. Instead, my research provides evidence in favor of pathogen accumulation, with both changes in pathogen community composition and an increase in lesions associated with plants grown in A. petiolata invaded soils. Additionally, I showed that A. petiolata influences decomposer community composition, including ectomycorrhiza, and excludes nitrogen-fixing bacteria.