Exploring the effects of metallic toxicity on the seed germination and initial growth of Lavandula stoechas L. and Myrtus communis L.: Towards promoting the dissemination of aromatic plants in contaminated lands

The high accumulation of heavy metals (HMs) in soils is becoming a major ecological concern worldwide that negatively impacts all living organisms. Therefore, sustainable solutions are urgently needed to withstand these challenging circumstances and to maintain natural ecosystem functionality. Among the relevant solutions is to select well-adapted plant species and embed them in revegetation operations for degraded areas. In this study, the effects of different concentrations (0, 200, 400, and 600 mg L^–1) of cadmium (Cd), chromium (Cr), nickel (Ni), and lead (Pd) on the seed germination capacity and initial growth performance of two valuable aromatic plants (Lavandula stoechas L. and Myrtus communis L.) were tested. The germination of seeds was greatest in the control treatment (0 mg L^–1), while amplifying HM stress restricted germination. The results obtained showed that seeds of L. stoechas were unable to germinate in the presence of high doses of Cd (400 and 600 mg L^–1) and Ni (600 mg mg L^–1), and subsequently featuring increasing tolerance thresholds in the following order: Pb > Cr > Ni > Cd. Regardless of the HM used, M. communis seeds germinated at all concentrations, and germination increased in the following pattern of HM resistance: Cd > Ni > Cr > Pb. Seedlings of L. stoechas displayed better resistance to Ni and Pb, while M. communis seedlings were most strongly affected by Ni. Overall, the hypocotyl was typically more susceptible to different metal elements than the radicle. The ability of seeds to effectively emerge in a broad range of HM solutions indicates that both species can further establish and propagate in contaminated soils.