Context-dependency in soil microbial mediation of Schoenoplectus americanus response to salinity stress

Candice Y. Lumibao and Michael J. Blum, Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN, Lorena Torres Martinez, Ecology and Evolutionary Biology, University of California Riverside, Riverside, CA, J. Patrick Megonigal, Smithsonian Environmental Research Center, Edgewater, MD, Sunshine A. Van Bael, Ecology and Evolutionary Biology, Tulane University, New Orleans, LA

Background/Question/Methods
It is increasing recognized that microbes can enhance plant tolerance to environmental stress, however, the magnitude and stability of microbial mediation of exposure responses are not well understood. We addressed this deficit by examining whether microbial mediation of plant exposure responses is contingent on biotic and abiotic factors. Using ancestral and descendant cohorts of the salt marsh plant, Schoenoplectus americanus, genotypes recovered from two 100+ year coastal marsh seed banks, we conducted a common-garden experiment to assess microbial mediation of plant responses to salinity stress. We compared S. americanus productivity and phenotypic trait variations according to plant genotype, age cohort and provenance under high and low salinity stress with and without native soil inoculant. We also examined how and whether associated microbial communities parallel or reflect these plant trait variations.
Results/Conclusions
We found that microbial mediation of salinity tolerance and related functional outcomes of plant-microbe associations are not only context-dependent but also dynamic, where associations differ among populations and over time. We observed temporal shifts in genotypic variation and G×E interactions. Correlation analyses between microbial communities and plants traits further revealed dynamic associations, differing between fungi and bacteria. These findings indicate the dynamic and context-dependency of microbial mediation of plant response to salinity stress. They also suggest that evolution can shape the fate of marsh ecosystems by altering how microbes confer tolerance to pressures linked to global change.