Foliar Application of Selenium under Nano Silicon on <i>Artemisia annua</i>: Effects on Yield, Antioxidant Status, Essential Oil, Artemisinin Content and Mineral Composition

The unique biological properties of <i>A. annua</i> have stimulated the research on its cultivation in different regions of the world. In this study, the effect of the Se and nano-Si supply on the yield, biochemical characteristics and mineral content of <i>A. annua</i> was investigated. Growth stimulation and a significant increase in the antioxidant status were recorded under Se and nano-Si foliar application. A decrease in the number of essential oil components and significant changes in the essential oil amount and composition led to significant phenophase shifts: nano-Si significantly stimulated eucalyptol and artemisia ketone accumulation and decreased germacrene D production, whereas Se demonstrated the opposite effect. A joint Se and nano-Si supply significantly decreased the camphor content and increased artemisia ketone and artemisinin levels by 1.3–1.5 times. Se/Si supplementation affected the macro- and microelements content, causing either a redistribution of leaves/stems elements (Al, Li and Zn) or a significant decrease in Ca, Mg, K, B, Cu, Fe and Mn concentrations in leaves, with no signs in growth inhibition or a decrease in the photosynthetic pigments content. The biofortification of <i>A. annua</i> with Se singly or in combination with nano-Si resulted in the synthesis of products with a Se content of as much as approximately 16% of the daily adequate Se consumption level (ACL) when using 5 g day⁻¹ as a spice, or 36% of ACL when using 50 mL of tea infusion (1:2, <i>v</i>/<i>w</i>). The results indicated a high possibility of Se and nano-Si application toward the regulation of <i>A. annua</i> growth, biochemical characteristics (including essential oil and artemisinin) and mineral content.