Plant performance responds to intraspecific variation in soil inocula from individual Solidago clones

Plant-soil microbe interactions are a key determinant of plant community composition and structure, with each plant species generating a unique soil microbiota. However, the degree of intraspecific variation in plant-soil microbe interactions in controlling plant performance has been much less investigated. We examined the strength of plant-soil microbe interactions across Solidago altissima and Schizachyrium scoparium seedlings grown in soils cultured by 24 genotypes of S. altissima in a greenhouse setting to determine the level of variation within these two target species. We also quantified leaf chemical variation across S. altissima genotypes using HPLC characterization of foliar constituents as a potential driver of below-ground processes. The impacts of soil microbe-mediated effects of genotypes ranged from negative to positive for both target species. Target species responses to the 24 soil microbial communities were positively correlated, although the strength of plant-soil microbe interactions was related to foliar chemistry for S. scoparium, but not for S. altissima. The magnitude of impacts in soils pooled from all 24 S. altissima genotypes was more negative than the average impact of genotypes tested individually, suggesting that this methodology cannot be used to assess 'average' effects. Our results strongly argue that intraspecific variation in plant-soil microbe interactions may be a quite large source of variation in systems dominated by clonal plants. Furthermore, simple inocula pooling obscured this variation and resulted in a marked bias toward the more antagonistic components of the soil microbial community.