Light and substrate composition control root exudation rates at the initial stages of soilless lettuce cultivation

Plant root exudation is an inherent metabolic process that enhances various functions of the root system like the mobilization of nutrients and interactions with surrounding microbial communities. The role and extent of root exudation in soilless crop production is poorly investigated. Here, we analyzed soilless lettuce and show that the root exudation rate declines with plant age. Furthermore, the impact of light quality and substrate was assessed by growing soilless lettuce in 100% red light (660 nm), 100% blue light (450 nm), and white light (full-light spectrum) and in 100% perlite, 100% potting soil, or mixtures of both materials. Root exudates were collected at 10, 17 and 24 days after transplanting. The total carbon root exudation rate was influenced by light conditions and substrate composition at the earliest timepoint of the culture but not at later growth stages. The total carbohydrate exudation rate was significantly higher under pure blue and red light compared to white light. The impact of light depended on the presence of perlite in the substrate. The total phenolic compound exudation rate was most strongly influenced by the substrate composition and reached the highest level in either pure potting soil or pure perlite. These findings underscore the importance of root exudation during the initial stages of development. Light and growing media influence the exudation rate at this early stage, suggesting that exudation is an adaptive process of the soilless lettuce culture. HIGHLIGHTAt an initial stage of development, soilless lettuce exudation rates are high and modulated by light and substrate composition, whereas older plants show lower rates that are not influenced by these environmental conditions.