Selection strengthens the relationship between plant diversity and the metabolic profile of Plantago lanceolata

O_LIPlants growing in biodiverse communities often increase productivity, but how plant diversity impacts the metabolome and the underlying ecological and evolutionary processes remains unclear. This study investigated how plant species diversity and selection for growing in different diversity environments affects the leaf metabolome of Plantago lanceolata. C_LIO_LIWe compared the metabolites of plants derived from those that had been selected in the "Jena Experiment" for 17 years in plant communities with differing plant diversity with the metabolites of naive plants not subjected to this selection. The metabolic profiles of selected P. lanceolata phytometers were also compared after growing in experimental environments varying in plant species richness, soil history, and community plant history. C_LIO_LIResults showed volatile compound diversity in P. lanceolata decreased with plant species richness, primarily due to phenotypic plasticity rather than selection. Soil history further strengthened this relationship. Conversely, non-volatile compound diversity increased with plant species richness, but only in phytometers subjected diversity-driven selection. These effects were more pronounced when plants shared soil-plant history with their community. C_LIO_LIIn summary, our study revealed that both plastic and adaptative responses shape the metabolome of P. lanceolata in relation to plant diversity with these effects becoming stronger as plant and soil communities mature. C_LI