Foliar-applied silicon nanoparticles mitigate cadmium stress through physio-chemical changes to improve growth, antioxidant capacity, and essential oil profile of summer savory (Satureja hortensis L.).

The use of nanofertilizers is a promising method for enhancing plant productivity and mitigating environmental pollution. The aim of this study was to show the silicon nanoparticles (Si-NPs) effects on growth, water content, phenolic and flavonoid content, and essential oil (EO) profile in aerial parts of summer savory (Satureja hortensis L.) in cadmium (Cd)-contaminated soil. The pot experiment was conducted with Cd concentration (0, 10, and 20 mg Cd kg soil) and foliar application of Si-NPs (0, 0.75, 1.5 and 2.25 mM of SO). The results revealed severe Cd stress (20 mg Cd kg soil) significantly decreased root and shoot weight, relative water content (RWC) but increased Cd accumulation in roots and shoots and proline concentration. Moderate Cd level (10 mg Cd kg soil) improved total phenolic content (TPC), total flavonoid content (TFC), and EO content. Under Cd stress, the 1.5 or 2.25 mM Si-NPs were highly effective concentrations to improve the growth and EO yield. The main EO constitutes were carvacrol (43.12-57.6%), γ-terpinene (20.56-25.6%), p-cymene (5.53-11.3%), and thymol (1.65-8.2%) with changes in their concentrations under Cd and Si-NPs. Heat map analysis (HMA) showed fresh weight, dry weight, and EO yield with a higher variation during these treatments had the most significant impact on distinguishing the clusters. The present study recommended 1.5-2.25 mM Si-NPs in improving the physio-biochemical status of summer savory plants to cope with Cd stress.