Discussion
Our study highlights that both plant-plant interactions and plant-soil
interactions can affect foliar and root metabolomic profiles viathe regulation of specific metabolites. We showed that metabolites that
were regulated in leaves differ from those in roots, and that for two of
our three plant species the number of regulated metabolites in leaves
was higher than in roots. These results partially confirm our first
hypothesis that both plant diversity and soil legacy can alter the
overall plant metabolome, as well as affect the regulation of specific
metabolites. Moreover, we revealed that the herbivore-induced
metabolomic response is modulated by plant-plant and plant-soil
interactions. This strongly suggests that the type and diversity of
biotic interactions in the environment can alter induced responses to
herbivores in plants. This confirms our second hypothesis that the
induced defense to herbivory is differently affected by plant diversity
and soil legacy. Compared to previous studies that focused on plant
diversity effects in a field experiment (e.g., Scherling et al., 2010)
or plant-soil feedback effects (Huberty et al., 2020; e.g., Ristok et
al., 2019), our study provides new insights towards disentangling plant
and soil diversity effects on plant metabolomes, and thus
plant-herbivore interactions.