COS 64-6 - CANCELLED - Elevated salinity influences invasion by Phragmites australis via changes in microbially-mediated stabilization and fitness differences

Abstract: Plant-soil feedbacks (PSF) profoundly influence patterns of plant species coexistence, dominance, and invasion. These interactions play out across a backdrop of heterogenous abiotic conditions, yet little is known about how the abiotic environment influences PSF, and consequently, community dynamics. Furthermore, ecologists have an incomplete understanding of how abiotic contexts can affect invasion dynamics via alteration of PSF. Here, we explore the impact of salinity and microbes adapted to elevated salinity (inoculum) on PSF in marshes invaded by Phragmites australis in coastal Louisiana. Using a classic “home and away” PSF greenhouse experiment, we test the impact of salinity and inoculum on interactions among native-native and native-invasive species pairs. Most previous research that has explored relationships between PSF and species co-existence has focused on the degree to which PSF stabilizes or destabilizes species interactions. However, recent work has shown that PSF effects on plant coexistence depend not just on these stabilizing effects, but also on the degree to which they generate competitive fitness differences. We leverage this recent integration of plant–microbe interactions into modern coexistence theory to understand how PSF mediate the impacts of salinity on coexistence in invaded systems.

We find that salinity and inoculum operate synergistically to stabilize coexistence among native species. Within invasive-native interactions, salinity increases stabilization, but also produces large fitness differences that promote the exclusion of native species by Phragmites. Taken together, these results suggest that PSF may facilitate coexistence among native species in elevated salinity conditions but may promote invasion when Phragmites is introduced. This research underscores the importance of considering both stabilization and fitness differences when inferring the consequences of PSF for species coexistence. Additionally, this research offers novel insights about the complex relationships between the abiotic environment, PSF, and invasion. Understanding how shifting abiotic conditions differentially alter feedbacks among native and invasive species is particularly relevant to land managers and policy makers in predicting future invasion.