Soil microbiome effects on quantitative floral traits of the annual plant Mimulus guttatus

ABSTRACT Plant flowering is a critical determinant of fitness and supports pollination services to ecosystems. Flowers are energetically expensive and require nutrients that plants might otherwise use for growth. Soil microorganisms can alter plant development in a variety of ways, but the quantitative importance of microbiomes in determining floral variation has yet to be established. In particular, it is unclear the extent to which genotypic differences in flowering phenotypes are mediated through the microbiome. We used a two-generation plant-soil feedback design to test whether flowering traits in a short-lived annual plant Mimulus guttatus drive differentiation in rhizosphere microbiomes. Second, we tested whether these microbiomes subsequently affected flowering traits of progeny plants. We found that different plant genotypes did not generate differences in rhizosphere microbiome structure or diversity after eight weeks of growth. When these microbiomes were inoculated onto new plants, flowering traits were mainly driven by the progeny plant’s genotype and not the genotype of the parental plant that trained the inoculated microbiome. Longer microbial training, as would necessarily happen in perennial plants, may produce stronger effects, but our results suggest microbiome effects contribute mainly to the “environmental noise” in flower traits in the short-lived annual Mimulus guttatus .