COS 199-5 - CANCELLED - Microbial dynamics in Invasive Kentucky bluegrass and Native Switchgrass shed light on the mechanisms of plant invasion

Abstract: Invasive plants affect the diversity and integrity of ecosystems and, thereby, the world economy. Plant invasion threatens biodiversity since it contributes to the homogenization of native ecosystems. While previous studies have investigated the importance of physiological traits for plant invasion, our understanding of microbial contributions to plant invasion is limited. We know invasive plants can change soil attributes which might affect below-ground dynamics. Soil microbial communities determine plant growth, fitness, and stress tolerance. Beneficial microbes also help plants to access soil nutrients that are unavailable otherwise. An important question is whether invasive plants secrete specialized metabolites to recruit specific microbial groups that enable them to establish in a new range. Here we aim to uncover that by assessing microbial dynamics of invasive Kentucky bluegrass and native Switchgrass across five time points. We used Illumina MiSeq sequencing of 16S rRNA gene for bacteria and ITS for fungi in both roots and rhizosphere. Additionally, we collected root exudates from both plants across different time points and analyzed them using HPLC Mass Spectrometry. We found differences in the root, with Kentucky bluegrass having higher bacterial and fungal Shannon diversity than Switchgrass. Host plants and plant compartments structured the fungal and bacterial communities. In addition, we found a higher number of unique members in Kentucky bluegrass than in Switchgrass. Proteobacteria members dominated both the rhizosphere and root microbiota. Still, the Kentucky bluegrass rhizosphere had greater Xanthomonadales while the Switchgrass rhizosphere had more Burkholderiales members. Invasive Kentucky bluegrass also showed a greater abundance of Rhizophlyctidales in the roots, while native Switchgrass had Hypocreales. Rhizophlyctidales are known to be degraders, which can lead to more nutrients released in the soil, benefiting the plant and community. We also found distinct metabolite profiles for invasive and native plants that diverged over time. An overall enrichment in the metabolism of cofactors and vitamins was noted for Kentucky bluegrass. Moreover, a higher abundance of the phytochemical compound class was found in Kentucky bluegrass than in Switchgrass. Interestingly the bioactive peptide class seemed higher in Switchgrass than in Kentucky bluegrass across the time points. Overall, our results offer insights into the dynamics of microbial recruitment by invasive plants as well as the putative mechanisms by which invasive plants outcompete their native counterparts. The microbial and metabolite differences observed here could explain why Kentucky bluegrass is a strong invader of native ecosystems.