Soils from Different Solidago altissima Clones Mediate Intraspecific Interactions in Schizachyrium scoparium

While previous studies have examined plant intraspecific competition and soil microbial effects separately, fewer studies have investigated how these factors interact, particularly in the context of genotype-specific soil conditioning effects. Plant-soil feedbacks can significantly alter interspecific competitive outcomes, yet few studies have examined how local variation in soil conditioning influences plant responses to density-dependent competition. I investigated how soil inocula derived from four Solidago altissima clones that were previously shown to differ in their soil conditioning effects (Foster et al., 2022) affected the growth and root traits of Schizachyrium scoparium across a gradient of intraspecific competition (1, 2, or 4 plants per pot). Plants were grown in live versus autoclaved soil inocula from each clone for 60 days, and I measured total biomass, root mass fraction, specific root length, and root dry matter content. Differences between live and autoclaved soil treatments varied dramatically among S. altissima clones, with generally negative effects of live soil on S. scoparium biomass but complex, trait-specific responses that depended on both clone identity and plant density. Three-way interactions were significant in multiple traits, indicating that soil conditioning effects on intraspecific competition were highly context-dependent and clone-specific. These results suggest that different S. altissima clones condition soil environments in ways that create distinct competitive contexts for neighboring plants, potentially through differential soil microbial associations. My findings suggest that clone-specific soil conditioning effects within plant populations may be an underappreciated mechanism shaping competitive dynamics and community structure in grassland ecosystems.