Organ‐specific terpenoid responses in <i>Tanacetum vulgare</i> are chemotype‐dependent

Specialized metabolites such as terpenoids are known to mediate plant defence mechanisms. However, how terpenoid diversity governs inducible chemistry across organs remains poorly understood. We used three shoot terpenoid chemotypes of common tansy (Tanacetum vulgare) to test whether (i) root-chewing wireworms induce root terpenoids locally and alter shoot terpenoids systemically and (ii) phloem-feeding aphids induce a chemical response depending on chemotype, (iii) chemotypes differ in root-system development. Plants were grown in rhizotrons and monitored for 60 days. After root establishment, they were challenged with root-chewing wireworms (Agriotes spp.) and/or phloem-feeding aphids (Macrosiphoniella tanacetaria). Wireworms increased stored root sesquiterpenoid levels by more than twofold in chemotypes 1 and 2, whereas chemotype 3 was largely unresponsive. Aphids did not alter root terpenoids, but significantly increased shoot monoterpenoid emissions in chemotype 1 without affecting stored pools. Therefore, storage and emission were decoupled, and induction depended on both organ (roots versus shoots) and chemotype. Chemotype 1 also exhibited larger root systems than the others, consistent with its stronger inducibility. Our analysis reveals a compartmentalized, chemotype-specific defence strategy in tansy. This organ-specific separation of induction pathways suggests coordinated genetic control of terpenoid biosynthesis and release, and provides a phytochemical framework for understanding above- versus belowground herbivore interactions.