Plant-soil microbe interactions are increasingly appreciated as critical determinants of plant community diversity, structure and dynamics. While heterogeneity in soil microbes leads to differential plant performance, variation in the strength of plant-soil microbe interactions within species has been poorly explored. In clonal plants, where large areas of soil may be influenced by a single genetic individual, intra-specific variation may be a critical source of heterogeneity of plant-soil microbe interactions. We explored variation in plant-soil microbe interactions using 24 clones of Solidago altissima grown in a common garden. We also quantified chemical variation across these clones using HLPC of foliar constituents as a potential driver of below-ground processes. We used soils from these clones to inoculate two target species, S. altissima and the bunchgrass Schizachyrium scoparium to determine the magnitude of plant-soil microbe interactions. In addition, we tested a pooled inoculum composed of equal parts of each clone’s inoculum to determine whether that experimental methodology could adequately capture the mean interaction strength.
Results/Conclusions
Both target species exhibited marked variation in response to the soil microbes of the 24 S. altissima clones. Responses of each target species ranged from strongly negative to positive across clones. Target species responses were significantly, but weakly correlated across clones. Growth of S. scoparium was associated with plant chemistry, whereas S. altissima growth was not. The use of pooled soil inoculum did not capture the average effect of each clone’s soil microbes tested individually. Pooled inoculum resulted in significantly lower plant growth in both target species, reflecting dominance by the clones with the more negative influences on growth. Our results strongly argue that intraspecific variation in plant-soil microbe interactions may be a quite large, but largely unquantified source of variation in systems dominated by clonal plants. Furthermore, simple inocula pooling obscures this variation and resulted in a marked bias towards the more antagonistic components of the soil microbial community.