Effects of spatial setting of LED light source on yield, quality, and water-use efficiency in greenhouse tomato

In most parts of northern China, the light environment in facilities deteriorates owing to shortened sunshine time and weaker light intensity in winter. Artificial light supplementation is an effective method for alleviating the problems of vegetable growth, quality, and yield reduction caused by limited light. In this study, LEDs were used to examine different spatial settings (CK: no supplemental lighting; T1: upward supplemental lighting between plants; T2: downward supplemental lighting at the top of the plant; T3: downward supplemental lighting between plants; and T4: upward supplemental lighting at the bottom of the plant) on the biomass, yield, quality, water-use efficiency, and electric energy efficiency of 'Jingfan 502' tomato plants. LED supplemental light treatment significantly increased the dry and fresh weights of tomato overground and whole plants, decreased the dry matter distribution rate of stems, increased the dry matter distribution rate of leaves, increased the water-use efficiency of tomato plants, and increased the soluble sugar content, organic acid content, and sugar-acid ratio of tomato fruits. Among them, whole plant fresh weight, whole plant dry weight, fruit allocation ratio, yield, water-use efficiency, total sugar content, and sugar-acid ratio of tomatoes were the highest under the T4 treatment, with increases of 22.63%, 17.54%, 8.83%, 48.33%, 39.72%, 27.38%, and 6.5%, respectively, compared with CK. The electrical energy efficiency of plants under the T4 treatment was the highest at 32.84 g/kw. After principal component analysis of the 14 indicators, the composite scores were T4 > T2 > T3 > T1 > CK. The LED light source with bottom-upward supplemental light was the most suitable for tomatoes. The findings provide a theoretical basis for water-saving and high-quality production of overwintering tomatoes in a solar greenhouse in northern China.