One of the processes that may play a key role in plant species coexistence and
ecosystem functioning is plant–soil feedback, the effect of plants on
associated soil communities and the resulting feedback on plant performance.
Plant–soil feedback at the interspecific level (comparing growth on own soil
with growth on soil from different species) has been studied extensively,
while plant–soil feedback at the intraspecific level (comparing growth on own
soil with growth on soil from different accessions within a species) has only
recently gained attention. Very few studies have investigated the direction
and strength of feedback among different taxonomic levels, and initial results
have been inconclusive, discussing phylogeny, and morphology as possible
determinants. To test our hypotheses that the strength of negative feedback on
plant performance increases with increasing taxonomic level and that this
relationship is explained by morphological similarities, we conducted a
greenhouse experiment using species assigned to three taxonomic levels
(intraspecific, interspecific, and functional group level). We measured
certain fitness‐related aboveground traits and used them along
literature‐derived traits to determine the influence of morphological
similarities on the strength and direction of the feedback. We found that the
average strength of negative feedback increased from the intraspecific over
the interspecific to the functional group level. However, individual
accessions and species differed in the direction and strength of the feedback.
None of our results could be explained by morphological dissimilarities or
individual traits. Synthesis. Our results indicate that negative plant–soil
feedback is stronger if the involved plants belong to more distantly related
species. We conclude that the taxonomic level is an important factor in the
maintenance of plant coexistence with plant–soil feedback as a potential
stabilizing mechanism and should be addressed explicitly in coexistence
research, while the traits considered here seem to play a minor role