Silver birch (Betula pendula Roth) response to polycyclic aromatic hydrocarbons: implications for growth patterns and secondary metabolite production

Birches (Betula) are crucial trees in Northern Europe, enhancing forest resilience and biodiversity, and aiding in pollutant removal through phytoremediation. Industrialization and urbanization introduce polycyclic aromatic hydrocarbons (PAHs), threatening birch ecosystems and human health. This study investigated the impact of PAHs on the growth and secondary metabolite levels of silver birch (Betula pendula Roth) seedlings from four half-sib families (genetic groups). Seedlings were exposed to phenanthrene, pyrene, naphthalene, and fluoranthene at varying concentrations. Thirty-six compounds from birch leaf extracts were identified using LC–MS analysis, including catechin, quercitrin, caffeoylquinic acid. Significant findings included a reduction in shoot and root lengths, with phenanthrene at 200 µg L⁻¹ reducing shoot growth by up to 85% and root length by 69% in some families. Total phenol content increased in most families at higher pollutant concentrations, whereas total flavonoid content generally decreased. Notably, (epi)gallocatechin levels increased by up to 200% with naphthalene exposure, and catechin levels increased tenfold in some cases. The results underscore the differential responses among half-sib families to PAH exposure, with higher concentrations generally causing more pronounced negative effects on both growth and secondary metabolism. These findings emphasize the significance of secondary metabolites in plant–environment interactions, where alterations due to PAH exposure could affect birch resilience, and, consequently, the broader ecosystem functions they support.