effects of supplemental light quality at the end of day on herb production and some phytochemical properties of lemon balm (melissa officinalis l.)

Increasing day length during the short photoperiod in fall and winter is a beneficial method of increasing biomass production and altering plant morphology and phytochemistry. the objective of this study was to examine the effects of light quality at the end of the day (eod) on the growth and phytochemical characteristics of lemon balm. during shortday photoperiods in autumn, lemon balm (melissa officinalis l.) seedlings were exposed to red, blue, and combined red/blue light using light-emitting diodes for 2 hours at the eod. the results showed that exposure to red light significantly increased biomass. plants grown under blue light yielded the highest percentage of dry matter and their leaves had the highest chlorophyll content and flavonoids. the highest carotenoid content was found in plants irradiated with blue light and later with red+blue light. the highest levels of total phenols, anthocyanins, and antioxidant activity were found in plants grown under red light. in addition, light quality had a significant effect on essential oil content. the highest essential oil content was obtained in the red and red+blue light treatments. the light quality at the eod significantly changed the essential oil composition. the blue light significantly increased the citronellal content but decreased the geranial and linalool content. this study provided insights into the effects of eod light quality on plant growth and metabolite accumulation in lemon balm with a short photoperiod. in conclusion, supplemental light at the eod can effectively improve plant growth and secondary metabolite quality in medicinal plants.