BACKGROUND AND AIMS: Allelopathy may drive invasions of some exotic plants, although empirical evidence for this theory remains largely inconclusive. This could be related to the large intraspecific variability of chemically mediated plant-plant interactions, which is poorly studied. This study addressed intraspecific variability in allelopathy of Heracleum mantegazzianum (giant hogweed), an invasive species with a considerable negative impact on native communities and ecosystems. METHODS: Bioassays were carried out to test the alleopathic effects of H. mantegazzianum root exudates on germination of Arabidopsis thaliana and Plantago lanceolata. Populations of H. mantegazzianum from the Czech Republic were sampled and variation in the phytotoxic effects of the exudates was partitioned between areas, populations within areas, and maternal lines. The composition of the root exudates was determined by metabolic profiling using ultra-high-performance liquid chromatography with time-of-flight mass spectrometry, and the relationships between the metabolic profiles and the effects observed in the bioassays were tested using orthogonal partial least-squares analysis. KEY RESULTS: Variance partitioning indicated that the highest variance in phytotoxic effects was within populations. The inhibition of germination observed in the bioassay for the co-occurring native species P. lanceolata could be predicted by the metabolic profiles of the root exudates of particular maternal lines. Fifteen compounds associated with this inhibition were tentatively identified. CONCLUSIONS: The results present strong evidence that intraspecific variability needs to be considered in research on allelopathy, and suggest that metabolic profiling provides an efficient tool for studying chemically mediated plant-plant interactions whenever unknown metabolites are involved.

Faculty of Science Institute for Environmental Studies Charles University Prague Albertov 6 CZ 128 43 Prague 2 Czech Republic Institute of Botany Academy of Sciences of the Czech Republic CZ 252 43 Průhonice Czech Republic and Institute of Microbiology Academy of Sciences of the Czech Republic Vídeňská 1083 CZ 142 20 Prague 4 Czech Republic

Faculty of Science Institute for Environmental Studies Charles University Prague Albertov 6 CZ 128 43 Prague 2 Czech Republic Institute of Botany Academy of Sciences of the Czech Republic CZ 252 43 Průhonice Czech Republic and Institute of Microbiology Academy of Sciences of the Czech Republic Vídeňská 1083 CZ 142 20 Prague 4 Czech Republic Faculty of Science Institute for Environmental Studies Charles University Prague Albertov 6 CZ 128 43 Prague 2 Czech Republic Institute of Botany Academy of Sciences of the Czech Republic CZ 252 43 Průhonice Czech Republic and Institute of Microbiology Academy of Sciences of the Czech Republic Vídeňská 1083 CZ 142 20 Prague 4 Czech Republic

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