Based on a novel LC-MS based structural characterization method, Candidate Substrate Product Pair (CSPP), the aromatic metabolites of poplar wood and - bark will be characterized. By means of feeding experiments the biosynthetic pathways will also be elucidated. This will result in a thorough knowledge of the secondary metabolism of poplar. In addition this research will deliver an optimized CSPP-method that allows semi automatic characterization of metabolites.