Linking Populus nigra metabotypes to genetic variation and plant-herbivore interactions

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Black poplar (Populus nigra) has an immense diversity of specialized metabolites and is ideally suited for the analysis of plant-herbivore interactions. The objective of the first funding period was to assess the chemodiversity of constitutive and stress-induced volatile and non-volatile chemotypes in black poplars in response to feeding by Lymantria dispar and to determine the phenotypic plasticity of this response in relation to changes in gene expression. We showed that tree terpene emissions during herbivory exhibited origin-specific patterns and that the severity of feeding varied among genotypes. Analyses of P. trichocarpa, in a common garden at UBC Vancouver showed that metabolic differences in leaves could be explained by bioclimatic and geographic influences, allowing assignment of origins to individual river systems. A second funding period will determine the intraspecific chemodiversity and plasticity of black poplar organs under drought stress and above- and belowground herbivory. Drought stress is hypothesized to lead to changes in plant-herbivore interactions that result in organ-specific responses to herbivory. Experiments will be conducted on a rhizotron phenotyping platform whose non-invasive measurements will allow detection of stress-induced changes and provide tissue-specific samples for metabolomics analyses. For selected chemotypes, a multicuvette system is used to record gas exchange, including volatile organic compound emissions, from plants with high temporal resolution. Non-targeted metabolomics will be used to determine metabolome networks in various tissues and organs (young/old leaves, phloem/bark, xylem, and roots). This ‘metabolic atlas’ can be compared with the datasets from projects P1 and P3-P7 for Solanum dulcamara and Tanacetum vulgare. In collaboration with P8, we will investigate how metabolome networks are associated with changes in gene expression and genetic variation. In collaboration with P1, we will record the adaptability and fitness of different chemical phenotypes of black poplar under natural conditions in our joint common garden experiment. The chemodiversity plasticity experiment will be conducted at our facilities in Munich, and we will specifically conduct non-invasive analyses of optical biometric traits. The analyses in the project will contribute to the development of virtual plants (P9) and to the improvement of chemodiversity indices (P10), and will help to understand how chemodiversity is altered by environmental factors and what ecological consequences these changes may have for plant herbivory.