Copper- or Zinc-Fortified Nutrient Solution in Vertical Farming System Enriches Copper or Zinc and Elevates Phenolic Acid and Flavonoid Contents in Artemisia annua L

Artemisia annua L. is a well-known therapeutic herb that is widely used in folk medicine in Asian and African countries. A. annua can alleviate fever, wounds, and inflammation and is also popular as an anti-malarial agent. Cu and Zn are essential nutrients for human wellness and are vital to plants; they sometimes act as elicitors and induce stress mechanisms in plants to stimulate the production of secondary metabolites, which have bioactivities. Therefore, we added Cu or Zn to a nutrient solution and cultivated A. annua to enhance the Cu or Zn content. The Cu or Zn treatment during A. annua cultivation elevated their accumulation, and Zn showed a dramatic accumulation level in harvests. The aerial part of Zn16X contained 35 times higher Zn content than that of the control. Although the Cu or Zn contents were elevated, the plant height and yield were not affected, indicating the absence of toxic effects. The Cu or Zn treatment decreased the artemisinin content; however, these treatments increased the amounts of phenolic acids and flavonoids in A. annua. In particular, Zn4X showed a notable increase in the phenolic acids and flavonoids amounts. Moreover, the contents of certain types of caffeoylquinic acids were also highly elevated in Zn4X. Overall, Cu or Zn treatment in A. annua increased Cu or Zn accumulation and stimulated phenolic acid and flavonoid synthesis, which may have enhanced the therapeutic efficacy of A. annua.