Physiological and Oxidative Responses of Japanese Mint Grown Under Limited Water and Nitrogen Supplies in an Evaporated Greenhouse System

Abstract

Within this study, influences of abiotic factors inducing biomass and synthesis of secondary metabolites in Japanese mint (Mentha arvensis) were studied. Plants were cultivated in the evaporate greenhouse system under 50% shading, at temperatures of 25–28°C and with relative humidity of 60–65%. After 12 weeks of planting, the results showed that water management at 75% and 100% evaporate transpiration crops (ETc) gave the highest growth measures for plant height (22.96 cm), number of stems (7.75), stem thickness (3.69 mm), diameter of canopy (28.03 cm), number of leaves per plant (151.28), fresh weight (108.07 g), and dry weight (22.29 g), while leaf area value (1,104.10 cm2) was the highest at 75% water and the highest SPAD value was at 25% (41.13 SPAD unit). Levels of secondary metabolite as described by DPPH and ABTS antioxidant potential remained stable; however, total flavonoid was higher in ETc 25% and 50% as compared to other treatments (0.41 mg GAE/g DW). The content of menthol corresponded well with biomass yield. In the second experiment, nitrogen levels at 210 and 310 mg/l gave the highest in growth measures for plant height (21.41 cm) and SPAD unit (25.54 SPAD unit). In addition, the nitrogen level at 310 mg/l gave the highest growth measures, viz., number of stem (9.00 stems), stem thickness (3.28 mm), diameter of canopy (27.55 cm), number of leaves per plant (162.57), leaf area (568.38 cm2), fresh weight (80.79 g), and dry weight (17.09 g). At 12 weeks of cultivation, the highest levels of total phenolic and flavonoid and menthol were achieved when a higher rate of nitrogen was applied. The results advised that Japanese mints adjusted well to the stresses in the controlled atmospheric humidity of the greenhouse, and nitrogen was a key element for increasing the productivity.