Effect of different LED wavelengths on growth, chlorophyll and anthocyanin content of purple-red pakchoi (Brassica rapa chineensis) in indoor vertical farming

Abstract

Understanding the effects of different light wavelengths on plant growth and the accumulation of essential nutrients like antioxidants is critical for obtaining optimal light conditions for the production of high-quality vegetables in indoor vertical farming. Purplered pakchoi (Brassica rapa chineensisis) is a fast-growing brassiceous vegetable. This vegetable is known to have health-promoting properties due to anthocyanin, which is a crucial antioxidant in the diet. This crop was used to evaluate the effects of red (RL), blue (BL), and green (GL) wavelengths on plant morphology, relative chlorophyll content, and phytochemical accumulation (anthocyanin). Light treatments consisted of three different wavelength combinations: a) full spectrum, white light (WL) as a control (the proportions of RL, BL and GL wavelengths were 42%, 15% and 43%, respectively); b) combination RL81BL19 (the proportions of RL and BL wavelengths were set at 81% and 19%, respectively); and c) combination RL70BL21GL9 (the proportions of RL, BL and GL wavelengths were set at 70%, 21% and 9%, respectively). The experiment was carried out in the LED Light Research Lab (MARDI, Serdang), a walk-in chamber with a 12-hour photoperiod. The temperature, CO2, and relative humidity levels in the LED light lab were kept under control. Plant width and height were found to be most prominent in plants exposed under RL81BL19 LED light, followed by RL70BL21GL9, while plants grown under WL were relatively small. Purple-red pakchoi exposed to a combination of RL and BL, supplemented with GL light treatment, had a slightly smaller plant height and width than plants exposed to RL81BL19 light treatment. Similar results were obtained in terms of shoot fresh and dry weight, with the RL81BL19 having the highest shoot fresh and dry weight, followed by the RL70BL21GL9 and WL light exposure plants. Furthermore, when compared to other treatments, purple-red pakchoi treated with RL81BL19 light had a significantly higher content (p<0.05) of chlorophyll and anthocyanin. This finding indicated that GL light treatment has no direct effect on overall growth, chlorophyll accumulation, or anthocyanin content in purple-red pakchoi. This study found that the RL81BL19 wavelength is the best LED light treatment for purple-red pakchoi production in indoor vertical farming.