Differences in Growth Characteristics and Photochemical Responses of Salvia miltiorrhiza Bunge under Different LED Light Qualities in a Closed Plant Factory System

Background: Salvia miltiorrhiza Bunge, an important medicinal crop, is documented in China&quots oldest pharmacopoeia, Shennong Bencaojing. However, research on the effects of light quality on its growth and photochemical responses is limited.<br/>Methods and Results: This study utilized T5 light-emitting diode (LED) bars with red (630 ㎚), green (520 ㎚), blue (450 ㎚), purple phyto (450 ㎚, 650 ㎚, and far-red), warm white (3000 K), natural white (4100 K), and cool white (6500 K) lights. The results indicated that white LEDs enhanced the shoot growth, chlorophyll content (SPAD units) and root number of S. miltiorrhiza more effectively than monochromatic LEDs and purple phyto-LEDs. Far-red wavelengths, approximately 17.6% of which are included in the purple phyto-LEDs, have been suggested to influence root length positively. Biomass was heavier under white LEDs, suggesting the importance of including the full spectrum of wavelengths within the photosynthetically active radiation range. White LEDs provided superior growth and photochemical efficiency, with slight variations based on the types of white light. Although green LED alone had negative effects, green wavelengths may be more crucial than far-red wavelengths when included in a composite spectrum.<br/>Conclusions: S. miltiorrhiza exhibited optimal growth and photochemical responses under white LED lights. Although green LED light alone has negative effects, green wavelengths within a composite spectrum may play a more important role than far-red wavelengths. However, further research is required to confirm these findings and fully understand the specific contributions of each wavelength.