Biological invasions are widespread and contribute to biodiversity losses at regional and continental scales. However, the mechanisms underlying plant invasions are not well understood leading to difficulty predicting invasiveness of plants and invasibility of landscapes, and effectively managing invaded lands. Recent research suggests that the plant-associated microbiome may play a role in invasion processes if microbes more negatively or less positively affect native plant species than non-native species. Plant-soil feedback (PSF) experiments, which test soil microbial influences on plant productivity can reveal strong positive or negative controls of the total microbial community. However, these experiments do not often explore the identities of the microbes driving feedbacks making it difficult to determine which components of the diverse microbiome are most influential. For invasion biology, this means that traditional PSFs uncover little about actual invasion mechanisms, but only assess the net effect of different microbial components. We modified the typical PSF experiment to ask: 1) How do different components of the microbial community affect the strength of PSFs? 2) Are native and non-native plants differentially affected by various microbial constituents? Using native and non-native lineages of Phragmites australis, we performed a reciprocal transplant PSF experiment with targeted microbe manipulations to assess the effects of broad microbial components on plant productivity.
Results/Conclusions
Microbes either weakly affected or did not affect plant biomass in all treatments. This is consistent with prior published work stating that Phragmites’has relatively weak and negative plant-soil feedbacks. We treated conditioned soils with microbial inhibitors targeting fungi, bacteria, or oomycetes, and all factorial combinations. Feedbacks for native Phragmiteswere not different from zero across all inhibitor treatments. In contrast, the non-native Phragmitesdisplayed feedbacks ranging widely from negative to positive, depending upon the inhibitor treatment applied (Lineage x Inhibitor P= 0.036). This suggests that feedbacks in non-native Phragmitesare driven by complex interactions between microbial groups. We are assessing these changes in the microbial community using quantitative PCR and high throughput sequencing. Quantitative PCR allows us to assess the effectiveness and longevity of our inhibitor treatments while the sequencing effort allows us to identify community differences that could be driving changes in feedbacks. Targeted microbial manipulations elucidate the relative importance of various microbial groups in plant-soil feedbacks and could improve understanding of microbial mechanisms of invasion.