Genotypic Diversity Reduces the Negative Effects of Increased Competition, Herbivory, and Tidal Inundation on the Productivity of Spartina alterniflora

Genotypic diversity has the potential to function in a similar manner to species diversity, particularly in ecosystems dominated by a single foundational plant, and may promote stability in the face of disturbance. However, it has primarily been documented only in terrestrial species or in seagrasses. We conducted three separate experiments in which we compared plant production between monocultures and polycultures of the widely distributed salt marsh macrophyte Spartina alterniflora , exposed to increased levels of stress from competition, herbivory, and tidal inundation (simulating the effects of sea-level rise). Increased levels of disturbance reduced aboveground growth of monocultures in all three experiments, but greater clonal diversity offset the negative effects of increased levels of all the stressors in polycultures. Our results contribute to a growing body of literature demonstrating that genotypic diversity of a foundational species can function analogously to species diversity. They also highlight the potential importance of high levels of genotypic diversity in this species in determining the response to anthropogenic disturbances and in management or restoration efforts.