Evaluating Plant-Microbe Associations in Response to Environmental Stressors to Enhance Salt Marsh Restoration

Microorganisms can enhance nutrient acquisition or suppress diseases from pathogens, while plants can provide carbon resources and oxygen to root-associated microbes. However, human activities have altered nutrient cycles and disrupted such mutualisms. Therefore, we need to understand how to promote positive plant-microbe associations to aid in restoring coastal wetland ecosystems where human stressors and climate change (e.g., hurricanes, sea-level rise) challenge restoration outcomes. This study seeks to examine how salinity stressors influence plant-microbe relationships, where we hypothesize that the presence of microbes will buffer salinity stressor effects. We used a whole sediment inocula approach to test this hypothesis. We exposed marsh cordgrass ( Sporobolus alterniflorus ) plugs to a replicated factorial experiment with three levels of microbiome addition (microbial inocula, autoclaved microbial inocula, no microbe control) and two levels of salinity (<0.5 psu, 20 psu), replicated ten times. We added microbial inocula from the marsh site with autoclaved soilless media and exposed half the plugs to saltwater (20 psu) and half to freshwater (<0.5 psu). Results revealed that marsh microbial inocula additions during early plant development may ameliorate salinity stressors and could be critical for future restoration efforts. The addition of marsh microbial inocula provided a rescue effect from salinity stress, observed in plant height and aboveground biomass. Belowground biomass, bacterial diversity H’, and bacterial evenness J’ were similar across microbial and water treatments (ANOVA, NS); however, the main effects of water (PERMANOVA, R ² =0.100, P<0.001) and microbial (PERMANOVA, R ² =0.086, P<0.001) treatments significantly influenced the bacterial community composition. This work provides evidence that microbial stewardship is essential for buffering against environmental stressors and could promote plant establishment for wetland restoration.