3.1 Plant diversity or soil legacy effects on plant metabolomes
Neither plant diversity nor soil legacy had a significant effect on overall foliar or root metabolome composition (Table 1 ). However, when we compared metabolomes of plants grown in monocultures with conspecifics growing in mixtures, we discovered a total of 139 significantly up- or down-regulated metabolites in both leaves and roots (Fig. 1 ). Across both experiments, we found that more foliar than root metabolites were regulated in response to heterospecific plant-plant and plant-soil interactions inLeucanthemum vulgare (25 vs. 12) and Ranunculus acris (36 vs. 2; Fig. 1 ). Only in Geranium pratense were the metabolites in leaves (31 regulated metabolites) and roots (33 regulated metabolites) similarly responsive to heterospecific plant-plant or plant-soil interactions. Overall, metabolites in the leaves of R. acris were most responsive, followed by roots and leaves of G. pratense , and leaves of L. vulgare . Plant-plant interactions generally up- and down-regulated metabolites across all species, while plant-soil interactions mostly down-regulated metabolites in leaves and roots of G. pratense , but up-regulated metabolites in leaves of R. acris (Fig. 1 ).
We found that most regulated metabolites were uniquely synthesized by a plant in response to either plant-plant or plant-soil interactions (Fig. 2 ). This pattern was true across leaves and roots, and across plant species. The only exceptions to this pattern occurred in leaves of G. pratense and R. acris . Here, we detected metabolites that were regulated in response to both plant-plant and plant-soil interactions (Fig. 2 ). Moreover, we observed that plants grown either in plant-plant or plant-soil interaction, synthesized and regulated unique metabolites in leaves and roots (Appendix Fig. A1 ). The regulated metabolites that we could tentatively assign a molecular formula and compound class or name to, mostly belonged to phenolics, in particular flavonoids, their precursors, and derivatives (Table 2 ).