Regulation of Photomorphogenesis, Structural Quality, and Physiological Status in Sorrel (Rumex acetosa L.) Across LED Light Quality Treatments

Sorrel (Rumex acetosa L.) is a promising leafy vegetable for controlled-environment production, but integrated information on its growth, structural quality, optical traits, and photochemical responses to light-emitting diode (LED) spectra remains limited. To our knowledge, this study provides the first systematic comparison of five contrasting LED spectral conditions in sorrel using morphological, biomass, structural-quality, reflectance-based, and chlorophyll-fluorescence indicators. Plants were grown for six weeks under red light (RL), green light (GL), blue light (BL), purple-phyto light (PL) containing red, blue, and far-red components, or white light (WL) at a color temperature of 6500 K. Sorrel responses differed markedly among spectral environments and could not be explained by a single growth parameter. WL produced the highest mean shoot dry weight (505 mg), which was approximately 30.5% higher than that under PL (387 mg), although the difference between the two treatments was not statistically significant. WL also produced 46.5% greater leaf area than PL (50.1 versus 34.2 cm2) and showed the highest mean PIABS value (4.00). In contrast, PL showed the highest mean root dry weight (25.5 mg) and Dickson quality index (9.4), together with a relatively low shoot-to-root ratio (17.7) and top-heavy index (20.0), indicating a less shoot-biased structural pattern. BL restricted growth and leaf development and was associated with lower soil plant analysis development units, normalized difference vegetation index, photochemical reflectance index, Fv/Fm, and PIABS, indicating that BL alone may have limited suitability for sorrel cultivation under the present experimental conditions. Under the tested conditions, WL appeared more suitable for yield-oriented production, whereas PL may be considered when shoot–root structural balance is prioritized.