Effects of supplementary lighting with different spectral compositions on plant growth, fruit development, and quality formation of facility-grown tomatoes

Tomatoes cultivated in facility agriculture often encounter low-light stress in autumn, winter, and early spring. This study aimed to investigate the effects of supplementary lighting with different spectral compositions dominated by red-blue (RB) light on plant growth, fruit development, and quality formation of early spring facility-grown tomatoes. Six supplementary lighting treatments were set up: red-blue (RB), red-blue + red (RB + R), red-blue + blue (RB + B), red-blue + green (RB + G), red-blue + far-red (RB + FR), and red-blue + ultraviolet A (RB + UVA). The treatment with no supplementary lighting served as the control (CK), and supplementary lighting was provided from 06:00 to 08:30 and from 18:30 to 22:00 daily. The results showed that, compared with CK, supplementary lighting with different spectral compositions significantly promoted plant growth, accelerated fruit ripening, and improved yield and quality (P < 0.05). Compared with the RB treatment, the RB + R treatment significantly increased the number of large fruits and yield per plant by 25.79% and 6.94%, respectively, demonstrating a superior effect on promoting yield formation over other treatments; the RB + B treatment was beneficial for increasing stem diameter and leaf SPAD value, and the contents of vitamin C and soluble protein were significantly higher than those in the RB treatment during the late stage of fruit development (fruit color-breaking stage and mature stage); the RB + G treatment had the highest average fruit weight, which was significantly increased by 8.29% compared with the RB treatment; during the late stage of fruit development, the contents of lycopene, soluble protein, amino acids, and total phenols in the RB + G treatment were significantly higher than those in the RB treatment, and the soluble sugar content and sugar-acid ratio was the highest at the fruit mature stage; the RB + FR treatment significantly increased the contents of soluble protein, soluble sugar, amino acids, and the sugar-acid ratio during the late stage of fruit development, and the fruit color parameters (a^* and b^* values) were significantly higher than those of the RB treatment; the RB + UVA treatment stimulated plant height growth in the short term and significantly increased the contents of soluble protein, soluble sugar, and organic acids during the late stage of fruit development. The results of this study provide a theoretical basis and technical reference for the regulation of the light environment in facility agriculture and the efficient production of facility-grown tomatoes.