The effect of light quality on the growth characteristics and photosynthetic performance of the Dracocephalum moldavica plant

Various aspects of light, including intensity, quality, and the period of light irradiation, affect plant growth and development, as well as their response to gas relations. In this study, the effect of different light spectra on growth characteristics, photosynthetic performance, and phenolic content of the D. moldavica plant were investigated. To this end, six light treatments including white light (w), red light (R), blue light (B) and three combined lights (R70B30, R50B50, and R30B70) emitted from LED lamps were used in a completely randomized design with three replications. The results revealed a significant effect of different light spectra on the studied traits at the 5% and 1% levels. The combined light of R70B30 improved plant growth charactristics. The height of plants grown in the red light treatment was the highest compared to other treatments. The highest fresh and dry weights of the shoot were observed in the R70B30 light spectrum, and the lowest in the blue light spectrum. Growth indices decreased with increasing proportions of blue light and improved with increasing proportions of red light. The maximum content of photosynthetic pigments was recorded in the combination of red and blue lights. The highest fluorescence intensity in all stages of the OJIP test was observed with red light, and the lowest fluorescence value was recorded with the combined lights of R50B50 and R70B30. The efficiency of the photosystem II water splitting system (Fv/F0) and the maximum efficiency of the photosystem (F _v /F _m ) were minimal in the red light treatment. Red light lowered the efficiency index of the system per absorbed light (PI _ABS ) and increased the quantum yield of energy loss (ΦD ₀ ), the light absorption rate per reaction center (ABS/RC), and the electron capture rate (TR ₀ /RC). The highest total phenolic content and antioxidant capacity were observed in plants grown under the R70B30 light conditions. The highest essential oil content (2.07% vol/wt) was observed in the R70B30 light environment, showing a 113.4% increase compared to white light.