Increasing the Ratio of Blue to Red Light Improves Growth and Phytochemical Content in Hydrocotyle bonariensis

Abstract

Artificial light has proved useful for optimal and consistent production of high-quality plants and plant produce. Among artificial light sources, light-emitting diodes (LED) offer advantages for indoor cultivation including narrow and customisable light spectra, lower heat production and higher energy efficiency. With the aim to improve both productivity and nutritional quality of Hydrocotyl bonariensis Lam. (largeleaf pennywort), phenotypical and phytochemical responses were assayed for plants grown under natural light and under four different spectral compositions of LED lighting: (1) red and blue (R : B = 83 : 35), (2) red and blue with a higher blue irradiance (R : B = 83 : 65), (3) red, blue and green (R : B : G = 83 : 35 : 12), and (4) red, blue and ultraviolet A (R : B : U = 83 : 35 : 10). Results show that the ratio of red to blue light has a substantial influence on plant growth and leaf biomass in H. bonariensis. Plants grown under the system with a higher level of blue irradiance showed the highest leaf number, total leaf area, leaf biomass, plant height, total antioxidant content, total phenol and total flavonoid content compared to plants grown under natural light in a greenhouse or the other LED conditions. The addition of green LED had a neutral effect on plant growth and on total antioxidant, phenol and flavonoid content while the addition of ultraviolet A LED had a negative effect on plant growth and on total antioxidant and phenol content. These findings provide fundamental information for the design of light sources, which will be useful for sustainable indoor cultivation of H. bonariensis and other pennywort species.