Localized Response of De Novo Terpenoid Emissions Through the Jasmonate Signaling Cascade in Two Main European Tree Species.

The systemically induced production of volatile organic compounds (VOCs) in undamaged tissues of plants under herbivore attack is still not fully understood, particularly with respect to below- and aboveground signaling. Here, we test the hypotheses that treatment of trees with jasmonic acid (JA) to simulate local herbivory (i) systemically induces VOC emissions in leaves and roots by signal propagation via the vascular bundle system and (ii) that bidirectional signaling occurs between below- and aboveground organs. We applied JA to roots and branches of Fagus sylvatica and Picea abies in a controlled experiment and shielded untreated tissues from volatile cues. VOC emissions and gas exchange were measured continuously over 6-8 days and complemented by quantification of tissue terpenoid storage pools. In contrast to the strong increase in terpenoid emissions from directly treated leaves and needles, which were mainly composed of sesquiterpenes, no systemically induced terpenoid emissions were found. Direct JA treatment of shoots reduced net photosynthesis and stomatal conductance in P. abies by ~50%, while the gas exchange of F. sylvatica remained unaffected. In the root system of P. abies, terpenoid contents increased both locally and systemically in response to belowground JA treatment. Overall, our results challenge the concept of systemically induced terpenoid emissions through vascular JA signaling, which is commonly induced in trees in response to insect herbivory. Instead, our data point toward a possible role of volatile cues in intra-plant signaling.