Grassland restoration reveals the importance of ecotypic variation on community assembly along a longitudinal aridity gradient

Two dominant species, Andropogon gerardii and Sorghastrum nutans, have a wide distribution across the Great Plains (USA) and are widely used in restorations. We ask: Do dominant species' ecotypes influence community diversity and structure evenly across a longitudinal aridity gradient? We established reciprocal common gardens at four sites across the gradient. Ecotypes of the two dominant species were seeded along with a prairie seed mix according to a randomized complete block design. Species composition was measured after 3 and 10 years. We used linear mixed models to analyze the effect of the ecotype and year on community diversity. NMDS and PERMANOVA were applied to examine the contribution of ecotype to community structure. Results showed that ecotype significantly affected species richness and shaped taxonomic, phylogenetic, and functional diversity. Accordingly, restorations should consider ecotypic variation as a critical biological filter to community assembly in grassland ecosystems.