Root traits and belowground herbivores relate toplant–soil feedback variation among congeners

Plant–soil feedbacks contribute to vegetation dynamics by species-specific interactionsbetween plants and soil biota. Variation in plant–soil feedbacks can be predicted by roottraits, successional position, and plant nativeness. However, it is unknown whether closelyrelated plant species develop more similar plant–soil feedbacks than more distantly relatedspecies. Where previous comparisons included plant species from distant phylogeneticpositions, we studied plant–soil feedbacks of congeneric species. Using eight intra-continentally range-expanding and nativeGeraniumspecies, we tested relations betweenphylogenetic distances, chemical and structural root traits, root microbiomes, and plant–soilfeedbacks. We show that root chemistry and specific root length better predict bacterial andfungal community composition than phylogenetic distance. Negative plant–soil feedbackstrength correlates with root-feeding nematode numbers, whereas microbiome dissimilarity,nativeness, or phylogeny does not predict plant–soil feedbacks. We conclude that rootmicrobiome variation among congeners is best explained by root traits, and that root-feedingnematode abundances predict plant–soil feedbacks.