Ecological consequences of genotypic diversity within a foundation plant, Spartina alterniflora, are pervasive but not universal across multiple stress gradients

Plant genotypic diversity can influence population- and community-level processes, yet we have limited understanding of how these effects vary across environmental gradients that are ubiquitous in nature.We conducted a 2-year field experiment manipulating plant (Spartina alterniflora) genotypic diversity across a natural stress gradient in tidal elevation, both with and without the addition of nutrients.Spartina diversity increased stem production, but the magnitude of this effect was reduced at both the most stressful and most benign endpoints of the combined elevation and nutrient gradient, consistent with recent species diversity studies. Complementarity among individuals likely underpins the observed benefit of Spartina diversity.Spartina diversity also affected the associated marsh community, with higher consumer (Littoraria irrorata) abundance in more diverse plots, owing to both greater Spartina density and increased variation in Spartina traits.Synthesis. The positive effects of Spartina diversity on population- and community-level responses under most environmental conditions highlights the ecological importance of plant genotypic diversity for the maintenance of function across the marsh landscape.

Automated summary

Plant genotypic diversity has positive effects on population and community-level processes in various environmental conditions, indicating its ecological importance for maintaining function across landscapes. A 2-year field experiment manipulating genotypic diversity in Spartina alterniflora across a natural stress gradient showed that diversity increased stem production, but the effect was reduced in extreme environmental conditions. The observed benefits were likely due to complementarity among individuals and resulted in increased density and variation of Spartina traits, affecting the associated marsh community.