Comparison of copper and zinc effects on growth, micro- and macronutrients status and essential oil constituents in pennyroyal (Mentha pulegium L.)

Abstract

Biosynthesis and metabolism of phytochemicals in aromatic and medicinal plants are vigorously affected by environmental agents. This study was undertaken to investigate the variations in the growth, nutrient status and the essential oils content and composition of pennyroyal (Mentha pulegium L.) plant exposed to different concentrations of copper (Cu; 0, 5, 25 mg kg−1 soil) and zinc (Zn; 0, 10, 50 mg kg−1 soil). The results of the plant treatment responses revealed that the highest plant height, shoot dry weight, essential oil content and yield were achieved in plants treated with Cu and Zn at 5 and 10 mg kg−1. Low Zn concentration showed a synergistic effect on the uptake of Cu, Fe, Mn and K, whereas it revealed **contrary effect on phosphorus (P) status. However, Cu in 5 mg kg−1 poses positive effect on Fe, Mn and P content in root and shoot tissues. Moreover, the addition of Cu and Zn especially at 5 and 10 mg kg−1 was the optimal level in increasing the status of K, Mn, Fe, Cu and Zn in shoot, infusion and decoction. The constituents and quality of M. pulegium essential oils in terms of its major volatile components, namely pulegone, cis-isopulegone, α-pinene, sabinene, 1,8-cineol and thymol, improved significantly with Cu and Zn treatment as compared to control. From this standpoint, M. pulegium can be grown as alternative crop for mildly Cu- and Zn-polluted agricultural soils without contamination of the its industrial products.