Effects of hybridization on chemical diversity and plant–insect herbivore interactions in <i>Salix alba×fragilis</i>

Hybridization can create novel chemical traits and enhance plant adaptability to diverse environments. This study examined the effects of hybridization on chemical diversity and ecological interactions in Salix alba×fragilis hybrids from the Elbe River basin (Czechia). We analysed leaf metabolites of hybrids and their parental species for concentration, richness, and structural α- and β-diversity, linking them to herbivorous insect assemblages and soil conditions. Hybrids exhibited intermediate metabolite concentration and richness but showed higher structural α-diversity and distinct structural β-diversity compared with their parents. Hybrid-specific metabolites were structurally related to parental metabolites, indicating minor structural modifications rather than major changes to metabolic pathways following hybridization. Herbivore assemblages were influenced by metabolite richness or structural α-diversity. However, insect group responses varied, and herbivory damage did not correlate with leaf chemistry or differ between hybrids and parents. Soil nitrogen correlated with metabolite structural β-diversity, with hybrids displaying greater chemical variation along nitrogen gradients. These results highlight that hybridization significantly altered structural metabolite diversity. Yet, the structural changes were relatively minor which, together with group-specific responses of herbivores, could explain their modest effect on herbivory. Instead, they may enable these hybrids to flexibly respond to soil conditions, possibly contributing to their widespread occurrence.